Fuel injectionFuel injection is a system for mixing fuel with air in an internal combustion engine. It has become the primary fuel delivery system used in automotive petrol engines, having almost completely replaced carburetors in the late 1980s.

A fuel injection system is designed and calibrated specifically for the type(s) of fuel it will handle. Most fuel injection systems are for gasoline or diesel applications. With the advent of electronic fuel injection (EFI), the diesel and gasoline hardware has become similar. EFI's programmable firmware has permitted common hardware to be used with different fuels.

Carburetors were the predominant method used to meter fuel on gasoline engines before the widespread use of fuel injection. A variety of injection systems have existed since the earliest usage of the internal combustion engine.

The primary difference between carburetors and fuel injection is that fuel injection atomizes the fuel by forcibly pumping it through a small nozzle under high pressure, while a carburetor relies on low pressure created by intake air rushing through it to add the fuel to the airstream.

ObjectivesThe functional objectives for fuel injection systems can vary. All share the central task of supplying fuel to the combustion process, but it is a design decision how a particular system will be optimized. There are several competing objectives such as:

power output fuel efficiency emissions performance ability to accommodate alternative fuels reliability driveability and smooth operation initial cost maintenance cost diagnostic capability range of environmental operation

Certain combinations of these goals are conflicting, and it is impractical for a single engine control system to fully optimize all criteria simultaneously. In practice, automotive engineers strive to best satisfy a customer's needs competitively. The modern digital electronic fuel injection system is far more capable at optimizing these competing objectives consistently than a carburetor. Carburetors have the potential to atomize fuel better (see Pogue and Allen Caggiano patents).

Benefits[edit] Engine operation

Operational benefits to the driver of a fuel-injected car include smoother and more dependable engine response during quick throttle transitions, easier and more dependable engine starting, better operation at extremely high or low ambient temperatures, increased maintenance intervals, and increased fuel efficiency. On a more basic level, fuel injection does away with the choke which on carburetor-equipped vehicles must be operated when starting the engine from cold and then adjusted as the engine warms up.

An engine's air/fuel ratio must be precisely controlled under all operating conditions to achieve the desired engine performance, emissions, driveability, and fuel economy. Modern electronic fuel-injection systems meter fuel very accurately, and use closed loop fuel-injection quantity-control based on a variety of feedback signals from an oxygen sensor, a mass airflow (MAF) or manifold absolute pressure (MAP) sensor, a throttle position (TPS), and at least one sensor on the crankshaft and/or camshaft(s) to monitor the engine's rotational position. Fuel injection systems can react rapidly to changing inputs such as sudden throttle movements, and control the amount of fuel injected to match the engine's dynamic needs across a wide range of operating conditions such as engine load, ambient air temperature, engine temperature, fuel octane level, and atmospheric pressure.

A multipoint fuel injection system generally delivers a more accurate and equal mass of fuel to each cylinder than can a carburetor, thus improving the cylinder-to-cylinder distribution. Exhaust emissions are cleaner because the more precise and accurate fuel metering reduces the concentration of toxic combustion byproducts leaving the engine, and because exhaust cleanup devices such as the catalytic converter can be optimized to operate more efficiently since the exhaust is of consistent and predictable composition.

Fuel injection generally increases engine fuel efficiency. With the improved cylinder-to-cylinder fuel distribution, less fuel is needed for the same power output. When cylinder-to-cylinder distribution is less than ideal, as is always the case to some degree with a carburetor or throttle body fuel injection, some cylinders receive excess fuel as a side effect of ensuring that all cylinders receive sufficient fuel. Power output is asymmetrical with respect to air/fuel ratio; burning extra fuel in the rich cylinders does not reduce power nearly as quickly as burning too little fuel in the lean cylinders. However, rich-running cylinders are undesirable from the standpoint of exhaust emissions, fuel efficiency, engine wear, and engine oil contamination. Deviations from perfect air/fuel distribution, however subtle, affect the emissions, by not letting the combustion events be at the chemically ideal (stoichiometric) air/fuel ratio. Grosser distribution problems eventually begin to reduce efficiency, and the grossest distribution issues finally affect power. Increasingly poorer air/fuel distribution affects emissions, efficiency, and power, in that order. By optimizing the homogeneity of cylinder-to-cylinder mixture distribution,

all the cylinders approach their maximum power potential and the engine's overall power output improves.

A fuel-injected engine often produces more power than an equivalent carbureted engine. Fuel injection alone does not necessarily increase an engine's maximum potential output. Increased airflow is needed to burn more fuel, which in turn releases more energy and produces more power. The combustion process converts the fuel's chemical energy into heat energy, whether the fuel is supplied by fuel injectors or a carburetor. However, airflow is often improved with fuel injection, the components of which allow more design freedom to improve the air's path into the engine. In contrast, a carburetor's mounting options are limited because it is larger, it must be carefully oriented with respect to gravity, and it must be equidistant from each of the engine's cylinders to the maximum practicable degree. These design constraints generally compromise airflow into the engine. Furthermore, a carburetor relies on a restrictive venturi to create a local air pressure difference, which forces the fuel into the air stream. The flow loss caused by the venturi, however, is small compared to other flow losses in the induction system. In a well-designed carburetor induction system, the venturi is not a significant airflow restriction.

Fuel is saved while the car is coasting because the car's movement is helping to keep the engine rotating, so less fuel is used for this purpose. Control units on modern cars react to this and reduce or stop fuel flow to the engine reducing wear on the brakes.[citation needed]

Basic function

The process of determining the necessary amount of fuel, and its delivery into the engine, are known as fuel metering. Early injection systems used mechanical methods to meter fuel (non electronic, or mechanical fuel injection). Modern systems are nearly all electronic, and use an electronic solenoid (the injector) to inject the fuel. An electronic engine control unit calculates the mass of fuel to inject.

Modern fuel injection schemes follow much the same setup. There is a mass airflow sensor or manifold absolute pressure sensor at the intake, typically mounted either in the air tube feeding from the air filter box to the throttle body, or mounted directly to the throttle body itself. The mass airflow sensor does exactly what its name implies; it senses the mass of the air that flows past it, giving the computer an accurate idea of how much air is entering the engine. The next component in line is the Throttle Body. The throttle body has a throttle position sensor mounted onto it, typically on the butterfly valve of the throttle body. The throttle position sensor (TPS) reports to the computer the position of the throttle butterfly valve, which the ECM uses to calculate the load upon the engine. The fuel system consists of a fuel pump (typically mounted in-tank), a fuel pressure regulator, fuel lines (composed of either high strength plastic, metal, or reinforced

rubber), a fuel rail that the injectors connect to, and the fuel injector(s). There is a coolant temperature sensor that reports the engine temperature to the ECM, which the engine uses to calculate the proper fuel ratio required. In sequential fuel injection systems there is a camshaft position sensor, which the ECM uses to determine which fuel injector to fire. The last component is the oxygen sensor. After the vehicle has warmed up, it uses the signal from the oxygen sensor to perform fine tuning of the fuel trim.

The fuel injector acts as the fuel-dispensing nozzle. It injects liquid fuel directly into the engine's air stream. In almost all cases this requires an external pump. The pump and injector are only two of several components in a complete fuel injection system.

In contrast to an EFI system, a carburetor directs the induction air through a venturi, which generates a minute difference in air pressure. The minute air pressure differences both emulsify (premix fuel with air) the fuel, and then acts as the force to push the mixture from the carburetor nozzle into the induction air stream. As more air enters the engine, a greater pressure difference is generated, and more fuel is metered into the engine. A carburetor is a self-contained fuel metering system, and is cost competitive when compared to a complete EFI system.

An EFI system requires several peripheral components in addition to the injector(s), in order to duplicate all the functions of a carburetor. A point worth noting during times of fuel metering repair is that early EFI systems are prone to diagnostic ambiguity. A single carburetor replacement can accomplish what might require numerous repair attempts to identify which one of the several EFI system components is malfunctioning. Newer EFI systems since the advent of OBD II diagnostic systems, can be very easy to diagnose due to the increased ability to monitor the realtime data streams from the individual sensors. This gives the diagnosing technician realtime feedback as to the cause of the drivability concern, and can dramatically shorten the number of diagnostic steps required to ascertain the cause of failure, something which isn't as simple to do with a carburetor. On the other hand, EFI systems require little regular maintenance; a carburetor typically requires seasonal and/or altitude adjustments.

Typical EFI components Injectors Fuel Pump Fuel Pressure Regulator ECM - Engine Control Module; includes a digital computer and circuitry to

communicate with sensors and control outputs. Wiring Harness Various Sensors (Some of the sensors required are listed here.)

Crank/Cam Position: Hall effect sensor Airflow: MAF sensor, sometimes this is inferred with a MAP sensor Exhaust Gas Oxygen: Oxygen sensor, EGO sensor, UEGO sensor

Functional description Central to an EFI system is a computer called the Engine Control Unit (ECU), which monitors engine operating parameters via various sensors. The ECU interprets these parameters in order to calculate the appropriate amount of fuel to be injected, among other tasks, and controls engine operation by manipulating fuel and/or air flow as well as other variables. The optimum amount of injected fuel depends on conditions such as engine and ambient temperatures, engine speed and workload, and exhaust gas composition.

The electronic fuel injector is normally closed, and opens to inject pressurized fuel as long as electricity is applied to the injector's solenoid coil. The duration of this operation, called the pulse width, is proportional to the amount of fuel desired. The electric pulse may be applied in closely-controlled sequence with the valve events on each individual cylinder (in a sequential fuel injection system), or in groups of less than the total number of injectors (in a batch fire system).

Since the nature of fuel injection dispenses fuel in discrete amounts, and since the nature of the 4-stroke-cycle engine has discrete induction (air-intake) events, the ECU calculates fuel in discrete amounts. In a sequential system, the injected fuel mass is tailored for each individual induction event. Every induction event, of every cylinder, of the entire engine, is a separate fuel mass calculation, and each injector receives a unique pulse width based on that cylinder's fuel requirements.

It is necessary to know the mass of air the engine "breathes" during each induction event. This is proportional to the intake manifold's air pressure/temperature, which is proportional to throttle position. The amount of air inducted in each intake event is known as "air-charge", and this can be determined using several methods. (See MAF sensor, and MAP sensor.)

The three elemental ingredients for combustion are fuel, air and ignition. However, complete combustion can only occur if the air and fuel is present in the exact stoichiometric ratio, which allows all the carbon and hydrogen from the fuel to combine with all the oxygen in the air, with no undesirable polluting leftovers. Oxygen sensors monitor the amount of oxygen in the exhaust, and the ECU uses this information to adjust the air-to-fuel ratio in real-time.

To achieve stoichiometry, the air mass flow into the engine is measured and multiplied by the stoichiometric air/fuel ratio 14.64:1 (by weight) for gasoline. The required fuel mass that must be injected into the engine is then translated to the required pulse width for the fuel injector. The stoichiometric ratio changes as a function of the fuel; diesel, gasoline, ethanol, methanol, propane, methane (natural gas), or hydrogen.

Deviations from stoichiometry are required during non-standard operating conditions such as heavy load, or cold operation, in which case, the mixture ratio can range from

10:1 to 18:1 (for gasoline). In early fuel injection systems this was accomplished with a thermotime switch.

Pulse width is inversely related to pressure difference across the injector inlet and outlet. For example, if the fuel line pressure increases (injector inlet), or the manifold pressure decreases (injector outlet), a smaller pulse width will admit the same fuel. Fuel injectors are available in various sizes and spray characteristics as well. Compensation for these and many other factors are programmed into the ECU's software.

Multi-point fuel injectionMulti-point fuel injection injects fuel into the intake port just upstream of the cylinder's intake valve, rather than at a central point within an intake manifold. MPFI (or just MPI) systems can be sequential, in which injection is timed to coincide with each cylinder's intake stroke, batched, in which fuel is injected to the cylinders in groups, without precise synchronization to any particular cylinder's intake stroke, or Simultaneous, in which fuel is injected at the same time to all the cylinders.

Many modern EFI systems utilize sequential MPFI; however, it is beginning to be replaced by direct injection systems in newer gasoline engines.

‘Mpfi’ stands for 'multi point (electronic) fuel injection'. This system injects fuel into individual cylinders, based on commands from the ‘on board engine management system computer’ – popularly known as the Engine Control Unit/ECU.

Mpfi Systems can either be : a) ‘Sequential’ i.e direct injection into individual cylinders against their suction strokes, or b) ‘Simultaneous’ i.e together

for all the four or whatever the number of cylinders, or c) ‘Group’ i.e into Cylinder-Pairs.

These techniques result not only in better ‘power balance’ amongst the cylinders but also in higher output from each one of them, along with faster throttle response.

Of these variants of Mpfi, 'Sequential' is the best from the above considerations of power balance/output.

‘Sefi’’, as advertised by Ford Ikon, stands for 'Sequential Electronic Fuel Injection', which technically is the best of the above variants of Mpfi. Hyundai/Maruti Mpfi systems are in fact Sefi too. Daewoo India had the (b) or (c) variants of above Mpfi systems on its Cielo/Matiz.

On the other hand, older Opel-Astra’s had a 'single point' fuel injection system, which is in between an Mpfi and the now obsolete Single-Carburettor systems.

The ‘Fuel Injectors’ are precision built ‘Solenoid Valves’, something like Washing Machine Water inlet Valves. These have either single or multiple ‘Orifices’ which ‘spray’ fuel into the Fuel inlet manifold of a Cylinder upon actuation, from a common

Rail/Header pressurised to around 3 bar, fed by a high pressure electrically drive fuel pump inside the Petrol tank of the Car.

The ‘on-board’ ECU primarily controls the Ignition Timing and quantity of fuel to be injected. The latter is achieved by means of controlling the ‘duration’ for which the Injector solenoid valve coil is kept energized – popularly known as the ‘pulse-width’.

In general, an ECU in turn is controlled by the ‘data input’ from a set of ‘SENSORS’ located all over the Engine and its Auxiliaries. These detect the various ‘operating states’ of the Engine and the performance desired out of it. Such Sensors constantly monitor : 1) Ambient Temperature, 2) Engine Coolant Temp., 3) Exhaust/manifold temp., 4) Exhaust ‘O2’ content, 5) Inlet manifold vacuum, 6) Throttle position, 7) Engine rpm, 8) Vehicle road speed, 9) Crankshaft position, 10) Camshaft position, etc.

Based on a ‘programmed’ interpretation of all this input data, the ECU gives the various ‘commands’ to the Engine’s fuel intake and spark ignition timing systems, to deliver an overall satisfactory performance of the Engine from start to shut down, including ‘emission control’.

To get the best out of an Mpfi System, one should use – a) The OE recommended Petrol Additives or the new generation ‘Premium’ Petrol’s REGULARLY and b) NEVER Tamper with the OE Wiring Harness of the Car – EVEN to install the ubiquitous Music System OR any other Electrical Accessory - other than those ‘approved’ OE/Dealer and designed to suit the Car’s Wiring Harness/CWH ‘Couplers’.

Common rail direct fuel injectionCommon rail direct fuel injection is a modern variant of direct fuel injection system for petrol and diesel engines.

Common rail fuel injector

On diesel engines, it features a high-pressure (over 1,000 bar/15,000 psi) fuel rail feeding individual solenoid valves, as opposed to low-pressure fuel pump feeding unit injectors (Pumpe Düse or pump nozzles). Third-generation common rail diesels now feature piezoelectric injectors for increased precision, with fuel pressures up to 1,800 bar/26,000 psi.

[edit] Principles

Solenoid or piezoelectric valves make possible fine electronic control over the fuel injection time and quantity, and the higher pressure that the common rail technology makes available provides better fuel atomisation. In order to lower engine noise the engine's electronic control unit can inject a small amount of diesel just before the main injection event ("pilot" injection), thus reducing its explosiveness and vibration, as well as optimising injection timing and quantity for variations in fuel quality, cold starting, and so on. Some advanced common rail fuel systems perform as many as five injections per stroke.[7]

Common rail engines require no heating up time[citation needed] and produce lower engine noise and emissions than older systems.

Diesel engines have historically used various forms of fuel injection. Two common types include the unit injection system and the distributor/inline pump systems (See diesel engine and unit injector for more information). While these older systems provided accurate fuel quantity and injection timing control they were limited by several factors:

They were cam driven and injection pressure was proportional to engine speed. This typically meant that the highest injection pressure could only be achieved at the highest engine speed and the maximum achievable injection pressure decreased as engine speed decreased. This relationship is true with all pumps, even those used on common rail systems; with the unit or distributor systems, however, the injection pressure is tied to the instantaneous pressure of a single pumping event with no accumulator and thus the relationship is more prominent and troublesome.

They were limited on the number of and timing of injection events that could be commanded during a single combustion event. While multiple injection events are possible with these older systems, it is much more difficult and costly to achieve.

For the typical distributor/inline system the start of injection occurred at a pre-determined pressure (often referred to as: pop pressure) and ended at a pre-determined pressure. This characteristic results from "dummy" injectors in the cylinder head which opened and closed at pressures determined by the spring preload applied to the plunger in the injector. Once the pressure in the injector reached a pre-determined level, the plunger would lift and injection would start.

In common rail systems a high pressure pump stores a reservoir of fuel at high pressure — up to and above 2,000 bars (29,000 psi). The term "common rail" refers to the fact that all of the fuel injectors are supplied by a common fuel rail which is nothing more than a pressure accumulator where the fuel is stored at high pressure. This accumulator supplies multiple fuel injectors with high pressure fuel. This simplifies the purpose of the high pressure pump in that it only has to maintain a commanded pressure at a target (either mechanically or electronically controlled). The fuel injectors are typically ECU-controlled. When the fuel injectors are electrically activated a hydraulic valve (consisting of a nozzle and plunger) is mechanically or hydraulically opened and fuel is sprayed into the cylinders at the desired pressure. Since the fuel pressure energy is stored remotely and the injectors are electrically actuated the injection pressure at the start and end of injection is very near the pressure in the accumulator (rail), thus producing a square injection rate. If the accumulator, pump, and plumbing are sized properly, the injection pressure and rate will be the same for each of the multiple injection events.

Emission standardEmissions standards are requirements that set specific limits to the amount of pollutants that can be released into the environment. Many emissions standards focus on regulating pollutants released by automobiles (motor cars) and other powered vehicles but they can also regulate emissions from industry, power plants, small equipment such as lawn mowers and diesel generators. Frequent policy alternatives to emissions standards are technology standards (which mandate the use of a specific technology) and emission trading.

Standards generally regulate the emissions of nitrogen oxides (NOx), sulfur oxides, particulate matter (PM) or soot, carbon monoxide (CO), or volatile hydrocarbons (see carbon dioxide equivalent).

[edit] Motor vehicles

[edit] Background

The first Indian emission regulations were idle emission limits which became effective in 1989. These idle emission regulations were soon replaced by mass emission limits for both petrol (1991) and diesel (1992) vehicles, which were gradually tightened during the 1990’s. Since the year 2000, India started adopting European emission and fuel regulations for four-wheeled light-duty and for heavy-dc. Indian own emission regulations still apply to two- and three-wheeled vehicles.

Current requirement is that all transport vehicles carry a fitness certificate that is renewed each year after the first two years of new vehicle registration.

On October 6, 2003, the National Auto Fuel Policy has been announced, which envisages a phased program for introducing Euro 2 - 4 emission and fuel regulations by 2010. The implementation schedule of EU emission standards in India is summarized in Table 1.[1]

Table 1: Indian Emission Standards (4-Wheel Vehicles)

Standard Reference Date Region

India 2000 Euro 1 2000 Nationwide

Bharat Stage II Euro 2 2001 NCR*, Mumbai, Kolkata, Chennai

2003.04 NCR*, 10 Cities†

2005.04 Nationwide

Bharat Stage III Euro 3

2005.04 NCR*, 10 Cities†

2010.04 Nationwide

Bharat Stage IV Euro 4 2010.04 NCR*, 10 Cities†

* National Capital Region (Delhi)

† Mumbai, Kolkata, Chennai, Bengaluru, Hyderabad, Ahmedabad, Pune, Surat, Kanpur and Agra

The above standards apply to all new 4-wheel vehicles sold and registered in the respective regions. In addition, the National Auto Fuel Policy introduces certain emission requirements for interstate buses with routes originating or terminating in Delhi or the other 10 cities.

For 2-and 3-wheelers, Bharat Stage II (Euro 2) will be applicable from April 1, 2005 and Stage III (Euro 3) standards would come in force from April 1, 2010.[2]

[edit] Trucks and buses

Exhaust gases from vehicles form a significant portion of air pollution which is harmful to human health and the environment

Emission standards for new heavy-duty diesel engines—applicable to vehicles of GVW > 3,500 kg—are listed in Table 2.

Table 2 Emission Standards for Diesel Truck and Bus Engines, g/kWh

Year Reference Test CO HC NOx PM

1992 - ECE R49 17.3-32.6 2.7-3.7 - -

1996 - ECE R49 11.20 2.40 14.4 -

2000 Euro I ECE R49 4.5 1.1 8.0 0.36*

2005† Euro II ECE R49 4.0 1.1 7.0 0.15

2010† Euro III

ESC 2.1 0.66 5.0 0.10

ETC 5.45 0.78 5.0 0.16

2010‡ Euro IV

ESC 1.5 0.46 3.5 0.02

ETC 4.0 0.55 3.5 0.03

* 0.612 for engines below 85 kW

† earlier introduction in selected regions, see Table 1 ‡ only in selected regions, see Table 1

More details on Euro I-III regulations can be found in the EU heavy-duty engine standards page.

[edit] Light duty diesel vehicles

Emission standards for light-duty diesel vehicles (GVW ≤ 3,500 kg) are summarized in Table 3. Ranges of emission limits refer to different classes (by reference mass) of light commercial vehicles; compare the EU light-duty vehicle emission standards page for

details on the Euro 1 and later standards. The lowest limit in each range applies to passenger cars (GVW ≤ 2,500 kg; up to 6 seats).

Table 3 Emission Standards for Light-Duty Diesel Vehicles, g/km

Year Reference CO HC HC+NOx NOx PM

1992 - 17.3-32.6 2.7-3.7 - - -

1996 - 5.0-9.0 - 2.0-4.0 - -

2000 Euro 1 2.72-6.90 - 0.97-1.70 0.14-0.25 -

2005† Euro 2 1.0-1.5 - 0.7-1.2 0.08-0.17 -

2010† Euro 30.640.800.95

-0.560.720.86

0.500.650.78

0.050.070.10

2010‡ Euro 40.500.630.74

-0.300.390.46

0.250.330.39

0.0250.040.06

† earlier introduction in selected regions, see Table 1

‡ only in selected regions, see Table 1

The test cycle has been the ECE + EUDC for low power vehicles (with maximum speed limited to 90 km/h). Before 2000, emissions were measured over an Indian test cycle.

Engines for use in light-duty vehicles can be also emission tested using an engine dynamometer. The respective emission standards are listed in Table 4.

Table 4 Emission Standards for Light-Duty Diesel Engines, g/kWh

Year Reference CO HC NOx PM

1992 - 14.0 3.5 18.0 -

1996 - 11.20 2.40 14.4 -

2000 Euro I 4.5 1.1 8.0 0.36*

2005† Euro II 4.0 1.1 7.0 0.15

* 0.612 for engines below 85 kW

† earlier introduction in selected regions, see Table 1

[edit] Light duty gasoline vehicles

[edit] 4-wheel vehicles

Emissions standards for gasoline vehicles (GVW ≤ 3,500 kg) are summarized in Table 5. Ranges of emission limits refer to different classes of light commercial vehicles (compare the EU light-duty vehicle emission standards page). The lowest limit in each range applies to passenger cars (GVW ≤ 2,500 kg; up to 6 seats).

Table 5 Emission Standards for Gasoline Vehicles (GVW ≤ 3,500 kg), g/km

Year Reference CO HC HC+NOx NOx

1991 - 14.3-27.1 2.0-2.9 -

1996 - 8.68-12.4 - 3.00-4.36

1998* - 4.34-6.20 - 1.50-2.18

2000 Euro 1 2.72-6.90 - 0.97-1.70

2005† Euro 2 2.2-5.0 - 0.5-0.7

2010† Euro 32.34.175.22

0.200.250.29

-0.150.180.21

2010‡ Euro 41.01.812.27

0.10.130.16

-0.080.100.11

* for catalytic converter fitted vehicles

† earlier introduction in selected regions, see Table 1 ‡ only in selected regions, see Table 1

Gasoline vehicles must also meet an evaporative (SHED) limit of 2 g/test (effective 2000).

[edit] 3- and 2-wheel vehicles

Emission standards for 3- and 2-wheel gasoline vehicles are listed in the following tables.[3]

Table 6 Emission Standards for 3-Wheel Gasoline Vehicles, g/km

Year CO HC HC+NOx

1991 12-30 8-12 -

1996 6.75 - 5.40

2000 4.00 - 2.00

2005 (BS II) 2.25 - 2.00

2010.04 (BS III) 1.25 - 1.25

Table 7 Emission Standards for 2-Wheel Gasoline Vehicles, g/km

Year CO HC HC+NOx

1991 12-30 8-12 -

1996 5.50 - 3.60

2000 2.00 - 2.00

2005 (BS II) 1.5 - 1.5

2010.04 (BS III) 1.0 - 1.0

Table 8 Emission Standards for 2- And 3-Wheel Diesel Vehicles, g/km

Year CO HC+NOx PM

2005.04 1.00 0.85 0.10

2010.04 0.50 0.50 0.05

[edit] Overview of the emission norms in India 1991 - Idle CO Limits for Gasoline Vehicles and Free Acceleration Smoke for

Diesel Vehicles, Mass Emission Norms for Gasoline Vehicles. 1992 - Mass Emission Norms for Diesel Vehicles.

1996 - Revision of Mass Emission Norms for Gasoline and Diesel Vehicles, mandatory fitment of Catalytic Converter for Cars in Metros on Unleaded Gasoline.

1998 - Cold Start Norms Introduced. 2000 - India 2000 (Eq. to Euro I) Norms, Modified IDC (Indian Driving Cycle),

Bharat Stage II Norms for Delhi. 2001 - Bharat Stage II (Eq. to Euro II) Norms for All Metros, Emission Norms for

CNG & LPG Vehicles. 2003 - Bharat Stage II (Eq. to Euro II) Norms for 11 major cities. 2005 - From 1 April Bharat Stage III (Eq. to Euro III) Norms for 11 major cities. 2010 - Bharat Stage III Emission Norms for 4-wheelers for entire country whereas

Bharat Stage - IV (Eq. to Euro IV) for 11 major cities. Bharat Stage IV also has norms on OBD (similar to Euro III but diluted)

[edit] CO2 emission

India’s auto sector accounts for about 18 per cent of the total CO2 emissions in the country. Relative CO2 emissions from transport have risen rapidly in recent years, but like the EU, currently there are no standards for CO2 emission limits for pollution from vehicles.

[edit] Obligatory labeling

There is also no provision to make the CO2 emissions labeling mandatory on cars in the country. A system exists in the EU to ensure that information relating to the fuel economy and CO2 emissions of new passenger cars offered for sale or lease in the Community is made available to consumers in order to enable consumers to make an informed choice.

[edit] Non road diesel engines

[edit] Construction machinery

Emission standards for diesel construction machinery were adopted on 21 September 2006. The standards are structured into two tiers:

Bharat (CEV) Stage II—These standards are based on the EU Stage I requirements, but also cover smaller engines that were not regulated under the EU Stage I.

Bharat (CEV) Stage III—These standards are based on US Tier 2/3 requirements.

The standards are summarized in the following table:

Table 9 Bharat (CEV) Emission Standards for Diesel Construction Machinery

Engine Power

Date

CO HC HC+NOx NOx PM

kW g/kWh

Bharat (CEV) Stage II

P < 8 2008.10 8.0 1.3 - 9.2 1.00

8 ≤ P < 19 2008.10 6.6 1.3 - 9.2 0.85

19 ≤ P < 37 2007.10 6.5 1.3 - 9.2 0.85

37 ≤ P < 75 2007.10 6.5 1.3 - 9.2 0.85

75 ≤ P < 130 2007.10 5.0 1.3 - 9.2 0.70

130 ≤ P < 560 2007.10 5.0 1.3 - 9.2 0.54

Bharat (CEV) Stage III

P < 8 2011.04 8.0 - 7.5 - 0.80

8 ≤ P < 19 2011.04 6.6 - 7.5 - 0.80

19 ≤ P < 37 2011.04 5.5 - 7.5 - 0.60

37 ≤ P < 75 2011.04 5.0 - 4.7 - 0.40

75 ≤ P < 130 2011.04 5.0 - 4.0 - 0.30

130 ≤ P < 560 2011.04 3.5 - 4.0 - 0.20

The limit values apply for both type approval (TA) and conformity of production (COP) testing. Testing is performed on an engine dynamometer over the ISO 8178 C1 (8-mode) and D2 (5-mode) test cycles. The Bharat Stage III standards must be met over the useful life periods shown in Table 10. Alternatively, manufacturers may use fixed emission deterioration factors of 1.1 for CO, 1.05 for HC, 1.05 for NOx, and 1.1 for PM.

Table 10 Bharat (CEV) Stage III Useful Life Periods

Power Rating

Useful Life Period

hours

< 19 kW 3000

19-37 kW

constant speed 3000

variable speed 5000

> 37 kW 8000

[edit] Agricultural tractors

Emission standards for diesel agricultural tractors are summarized in Table 11.

Table 11 Indian Emission Standards (4-Wheel Vehicles)

Standard Reference Date Region

India 2000 Euro 1 2000 Nationwide

Bharat Stage II Euro 2

2001 NCR*, Mumbai, Kolkata, Chennai

2003.04 NCR*, 11 Cities†

2005.04 Nationwide

Bharat Stage III Euro 3

2005.04 NCR*, 11 Cities†

2010.04 Nationwide

Bharat Stage IV Euro 4 2010.04 NCR*, 11 Cities†

* National Capital Region (Delhi)

† Mumbai, Kolkata, Chennai, Bangalore, Hyderabad, Secunderabad, Ahmedabad, Pune, Surat, Kanpur and Agra

Emissions are tested over the ISO 8178 C1 (8-mode) cycle. For Bharat (Trem) Stage III A, the useful life periods and deterioration factors are the same as for Bharat (CEV) Stage III, Table 10.

[edit] Electricity generation

[edit] Generator sets

Emissions from new diesel engines used in generator sets have been regulated by the Ministry of Environment and Forests, Government of India [G.S.R. 371 (E), 17 May 2002]. The regulations impose type approval certification, production conformity testing and labeling requirements. Certification agencies include the Automotive Research Association of India and the Vehicle Research and Development Establishment. The emission standards are listed below.

Table 12 Emission Standards for Diesel Engines ≤ 800 kW for Generator Sets

Engine Power (P) Date

CO HC NOx PM Smoke

g/kWh 1/m

P ≤ 19 kW

2004.01 5.0 1.3 9.2 0.6 0.7

2005.07 3.5 1.3 9.2 0.3 0.7

19 kW < P ≤ 50 kW

2004.01 5.0 1.3 9.2 0.5 0.7

2004.07 3.5 1.3 9.2 0.3 0.7

50 kW < P ≤ 176 kW 2004.01 3.5 1.3 9.2 0.3 0.7

176 kW < P ≤ 800 kW 2004.11 3.5 1.3 9.2 0.3 0.7

Engines are tested over the 5-mode ISO 8178 D2 test cycle. Smoke opacity is measured at full load.

Table 13 Emission Limits for Diesel Engines > 800 kW for Generator Sets

Date

CO NMHC NOx PM

mg/Nm3 mg/Nm3 ppm(v) mg/Nm3

Until 2003.06 150 150 1100 75

2003.07 - 2005.06 150 100 970 75

2005.07 150 100 710 75

Concentrations are corrected to dry exhaust conditions with 15% residual O2.

[edit] Power plants

The emission standards for thermal power plants in India are being enforced based on Environment (Protection) Act, 1986 of Government of India and it’s amendments from time to time.[4] A summary of emission norms for coal and gas based thermal power plants is given in Tables 14 and 15

Table 14 Environmental standards for coal & gas based power plants

Capacity Pollutant Emission limitCoal based thermal plants

Below 210 MWParticulate matter (PM) 350 mg/Nm3

210 MW & above   150 mg/Nm3500 MW & above   50 mg/Nm3Gas based thermal plants

400 MW & aboveNOX(V/V at 15% excess oxygen)

50 PPM for natural gas; 100 PPM for

naphtha

Below 400 MW & up to 100 MW

 

75 PPM for natural gas; 100 PPM for

naphtha

Below 100 MW  100 PPM for naphtha/natural gas

For conventional boilers   100 PPM

Table 15 Stack height requirement for SO2 control

Power Generation Capacity Stock Height (Metre)

Less than 200/210 MWe

H = 14 (Q)0.3 where Q is emission

rate of SO 2 in kg/hr,H = Stack height in metres

200/210 MWe

or less than 500 MWe 200 200500 MWe and

above

275 (+ Space provision for FGD

systems in future)

The norms for 500 MW and above coal based power plant being practised is 40 to 50 mg/Nm and space is provided in the plant layout for super thermal power stations for installation of flue gas desulphurisation (FGD) system. But FGD is not installed, as it is not required for low sulphur Indian coals while considering SO X emission from individual chimney.

In addition to the above emission standards, the selection of a site for a new power plant has to maintain the local ambient air quality as given in Table 16.

Table 16 Ambient air quality standard

Category

Conc. g/m3

SPM SO2 CO NOX

Industrial and mixed-use 500 120 5000 120Residential and rural 200 80 2000 80Sensitive 100 30 1000 30

Table 17 World bank norms for new projects

Existing Air Quality RecommendationSOX > 100 ?

g/m3 No projectSOX = 100 ?

g/m3

Polluted area, max. from a project

100 t/daySOX < 50 ?

g/m3

Unpolluted area, max. from a project

500 t/day

However the norms for SOX are even stricter for selection of sites for World Bank funded projects (refe r Table 2.4). For example, if SOX level is higher than 100 ? g/m 3, no project with further SOX emission can be set up; if SO X level is 100 ? g/m 3, it is called polluted area and maximum emission from a project should not exceed 100 t/day; and if SOX is less than 50 ? g/m 3, it is called unpolluted area, but the SOX emission from a project should not exceed 500 t/day. The stipulation for NOX emission is that it’s emission should not exceed 260 gram s of NOX per giga joule of heat input.

In view of the above, it may be seen that improved environment norms are linked to financing and are being enforced by international financial institutions and not by the policies/laws of land.

[edit] Fuels

Fuel Quality plays a very important role in meeting the stringent emission regulation.

The fuel specifications of Gasoline and Diesel have been aligned with the Corresponding European Fuel Specifications for meeting the Euro II, Euro III and Euro IV emission norms.

The use of alternative fuels has been promoted in India both for energy security and emission reduction Delhi and Mumbai have more than 100,000 commercial vehicles running on CNG fuel. Delhi has the largest number of CNG commercial vehicles running any where in the World. India is planning to introduce Biodiesel, Ethanol Gasoline blends in a phased manner and has drawn up a road map for the same. The Indian auto Industry is working with the authorities to facilitate for introduction of the alternative fuels. India has also setup a task force for preparing the Hydrogen road map. The use of LPG has also been introduced as an auto fuel and the oil industry has drawn up plans for setting up of Auto LPG dispensing station in major cities.

Indian Gasoline specifications:

Table 18

Sl. No

Characteristics Unit

Bharat

Stage II

Bharat

Stage III

Bharat

Stage IV

1 Density 15 0 C Kg/m3 710-770

720-775 720-775

2 Distillation       

3

a) Recovery up to 70 0 C(E70)

b) Recovery up to 100 0 C (E100)

c) Recovery up to 180 0 C (E180)

d) Recovery up to 150 0 C (E150)

e) Final Boiling Point (FBP), Max

f) Residue Max

%Volume

%Volume

%Volume

%Volume

0C

% Volume

10-45

40-70

90

-

210

2

10-45

40-70

-

75min

210

2

10-45

40-70

-

75min

210

2

4Research Octane Number (RON), Min

 88 91 91

5Anti Knock Index (AKI)/ MON, Min

  84 (AKI)

81 (MON)81

(MON)

6 Sulphur, Total , Max % mass 0.05150

mg/Kg50mg/Kg

7 Lead Content(as Pb), Max g/l 0.013 0.005 0.005

8Reid Vapour Pressure (RVP), Max

Kpa 35-60 60 60

9

Benzene, Content, Max

a)     For Metros

b)     For the rest

% Volume

-

3

5

1 1

10 Olefin content, Max%

Volume- 21 21

11 Aromatic Content, Max%

Volume- 42 35

Indian diesel specifications:

Table 19

S. No Characteristic BSII BSIII BSIV

1 Density Kg/m3 15 0 C 820-800 820-845 820-845

2 Sulphur Content mg/kg max 500 350 50

3(a) Cetane Number minimum and / or 48 51 51

3(b) Cetane Index or 46 and 46 and 46

4 Polycyclic Aromatic Hydrocarbon - 11 11

5

(a)

(b)

(c)

Distillation

Reco. Min. At 350 0 C

Reco. Min. At 370 0C

95%Vol Reco at 0o C max

85

95

-

-

-

360

-

-

360

Table 20 Diesel Fuel Quality in India

Date Particulars

1995 Cetane number: 45; Sulfur: 1%

1996 Sulfur: 0.5% (Delhi + selected cities)

1998 Sulfur: 0.25% (Delhi)

1999 Sulfur: 0.05% (Delhi, limited supply)

2000Cetane number: 48; Sulfur: 0.25% (Nationwide)

2001 Sulfur: 0.05% (Delhi + selected cities)

2005 Sulfur: 350 ppm (Euro 3; selected areas)

2010 Sulfur: 350 ppm (Euro 3; nationwide)

2010 Sulfur: 50 ppm (Euro 4; selected areas)

Indian bio-diesel specifications:

Table 21

S.No. Characteristics RequirementMethod of Test ,

ref to

    Other Methods[P:] of IS

1448

(1) (2) (3) (4) (5)

i. Density at 15°C, kg/m3 860-900 ISO 3675 P:16/

    ISO 12185 P:32

    ASTM

ii. Kinematic Viscosity at 40°C, cSt 2.5-6.0 ISO 3104 P:25

iii. Flash point (PMCC) °C, min 120 P:21

iv. Sulphur, mg/kg max. 50.0 ASTM D 5453 P:83

vCarbon residue (Ramsbottom) *,% by mass, max

0.05ASTM D 4530ISO

10370-

vi. Sulfated ash, % by mass, max 0.02 ISO 6245 P:4

vii. Water content, mg/kg, max 500 ASTM D 2709 P:40

    ISO 3733

    ISO 6296

viii Total contamination, mg/kg, max 24 EN 12662 -

ix Cu corrosion, 3 hrs at 50°C, max 1 ISO 2160 P:15

x Cetane No., min 51 ISO 5156 P:9

xi Acid value, mg KOH/g, max 0.50 - P:1 / Sec 1

xii Methanol @, % by mass, max 0.20 EN 14110 -

xiii Ethanol, @@ % by mass, max 0.20 -

xiv Ester content, % by mass, min 96.5 EN 14103 -

xv Free Glycerol, % by mass, max 0.02 ASTM D 6584 -

xvi Total Glycerol, % by mass, max 0.25 ASTM D 6584 -

xvii Phosphorous, mg/kg, max 10.0 ASTMD 4951 -

xviii Sodium & Potassium, mg/kg, max To report EN 14108 & -

      EN 14109 -

xix Calcium and Magnesium, mg/kg, To report ÷ -

max

xx Iodine value To report EN 14104 -

xxiOxidation stability, at 110°C hrs, min

6 EN 14112 -

* Carbon residue shall be run on 100% sample

** European method is under development

@ Applicable for Fatty Acid Methyl Ester

@@ Applicable for Fatty Acid Ethyl Ester

Gear cutting

[edit] Processes

[edit] BroachingMain article: Broaching

For very large gears or splines, a vertical broach is used. It consists of a vertical rail that carries a single tooth cutter formed to create the tooth shape. A rotary table and a Y axis are the customary axes available. Some machines will cut to a depth on the Y axis and index the rotary table automatically. The largest gears are produced on these machines.

Other operations such as broaching work particularly well for cutting teeth on the inside. The downside to this is that it is expensive and different broaches are required to make different sized gears. Therefore it is mostly used in very high production runs.

[edit] HobbingMain article: Hobbing

Hobbing is a method by which a hob is used to cut teeth into a blank. The cutter and gear blank are rotated at the same time to transfer the profile of the hob onto the gear blank.

The hob must make one revolution to create each tooth of the gear. Used very often for all sizes of production runs, but works best for medium to high.

[edit] MachiningMain article: Machining

Spur may be cut or ground on a milling machine or jig grinder utilizing a numbered gear cutter, and any indexing head or rotary table. The number of the gear cutter is determined by the tooth count of the gear to be cut.

To machine a helical gear on a manual machine, a true indexing fixture must be used. Indexing fixtures can disengage the drive worm, and be attached via an external gear train to the machine table's handle (like a power feed). It then operates similarly to a carriage on a lathe. As the table moves on the X axis, the fixture will rotate in a fixed ratio with the table. The indexing fixture itself receives its name from the original purpose of the tool: moving the table in precise, fixed increments. If the indexing worm is not disengaged from the table, one can move the table in a highly controlled fashion via the indexing plate to produce linear movement of great precision (such as a vernier scale).

There are a few different types of cutters used when creating gears. One is a rack shaper. These are straight and move in a direction tangent to the gear, while the gear is fixed. They have six to twelve teeth and eventually have to be moved back to the starting point to begin another cut.

A popular way to build gears is by form cutting. This is done by taking a blank gear and rotating a cutter, with the desired tooth pattern, around its periphery. This ensures that the gear will fit when the operation is finished.

[edit] ShapingMain article: Gear shaper

The old method of gear cutting is mounting a gear blank in a shaper and using a tool shaped in the profile of the tooth to be cut. This method also works for cutting internal splines.

Another is a pinion-shaped cutter that is used in a gear shaper machine. It is basically when a cutter that looks similar to a gear cuts a gear blank. The cutter and the blank must have a rotating axis parallel to each other. This process works well for low and high production runs.

[edit] Finishing

After being cut the gear can be finished by shaving, burnishing, grinding, honing or lapping.[1]

Pistons and Rings

Piston rings are not difficult to make IF you have the necessary formulae. There is a fine line between a piston ring which works, and another which is too weak (compressive wall force), too stiff (impossible to install without breakage), or otherwise unsuitable. The finest treatise on making custom piston rings can be found in the magazine Strictly IC, issues 7, 8, and 9. Editor Bob Washburn has all of the back issues. The author of the series on piston ring construction is Mr. George Trimble, and he approached the subject scientifically, deriving a method which will make great rings for any IC engine. The method makes use of a mandrel which holds the rings spread for heat treatment, and is based on ratios of ring thickness to bore.

The first step in preparing rings is to rough out (and then polish) the outside diameter of the rings from a fine-grained cast-iron bar. Tolerance is +.0006, -.0000. UNDERSIZED RINGS are a no-no, and will not work. The bore size of all my cylinders is 1.0003", +.0002, -.0002. Hence I needed this bar to measure 1.0005" minimum. I shot for 1.0005". The bar is turned to 1.0015", and the taper carefully measured. In my case it tapered .0004". I used silicon carbide wet-dry paper in grits 320, 600, 1200, 1500, and 2000 to SLOWLY remove the taper and polish the bar to a mirror finish. The paper is backed with a hardened steel parallel. Final dimension was within .0001 throughout the length.

The bore of the ring stock is cut. The grooves already cut in the piston measure .904" diameter. I elected to bore the ring stock to .914 to provide plenty of clearance. Final cuts were taken with a very minimal feed to remove spring from the tool, maybe 3 passes for the final .005". Internal taper was negligible.

Note the high finish on the OD of the ring stock compared to the turned finish in the above photo.

A mini-thin parting tool of width .027" was used to part the individual rings. Before parting, the outer rim is deburred with a hard arkansas stone, and partway through the stock, the tool is withdrawn and the inner OD rim is deburred as well. The ID rims are deburred after parting with a Cratex rubberized abrasive mounted in a Foredom hand tool. My engine uses 2 rings per piston... I planned on 36 rings, as many will be scrapped for one reson or another. The white stuff inside the bore is a paper towel shoved in to control ringing and chatter during parting.

After parting, the faces of the rings are lapped on a surface plate with progressively finer wet-dry, with 2000 grit producing a mirror finish.

The mandrel is shown here, constructed of 1018 steel with the formula derived from the SIC articles. Basically, the formulas give you the large mandrel size, the small dowel size (the small dowel opens the ring) and the distance between centers of the two.

The rings, after polishing, are split with ordinary wire cutters. This will usually cleave them cleanly, but perhaps one in ten will be discarded due to a jagged, uneven break. The survivors are slowly spread and mounted on the mandrel. The whole assy is then heated to 1475 deg. f. for 1/2 hour. Scale prevention is important... I used a double-wrapping of SS foil, with Nitrogen gas injected before sealing. I have used keepbryte in the past which works, but the SS foil is neater and easier to use.

After heat treatment, the rings retain their expanded set. The dark color is not scale... I was a bit anxious to open the SS envelope, and the whole assy was hot enough to darken the rings a bit. If you look closely, you can still see some rings mounted at the base of the mandrel. Note the gap in the loose rings... this is the set of the rings, not the traditional ring gap which must be cut after the rings are inserted into a bore.

Two pistons with ring grooves cut but without rings. The top groove is purely compression... the bottom groove is a combination compression and oil-control setup. Note the holes drilled axially. These holes are drilled after a band perhaps .005" deep is turned in the piston, and drain to the wrist pin cavity seen in the right hand piston. The lower ring scrapes the oil into this shallow groove, where it is forced back inside the piston.

A piston ring is an open-ended ring that fits into a groove on the outer diameter of a piston in a reciprocating engine such as an internal combustion engine or steam engine.

The three main functions of piston rings in reciprocating engines are:

1. Sealing the combustion/expansion chamber. 2. Supporting heat transfer from the piston to the cylinder wall. 3. Regulating engine oil consumption.[4] [1]

The gap in the piston ring compresses to a few thousandths of an inch when inside the cylinder bore.

[edit] Automotive

Most automotive pistons have three rings: The top two while also controlling oil are primarily for compression sealing (compression rings); the lower ring is for controlling the supply of oil to the liner which lubricates the piston skirt and the compression rings (oil control rings). Typical compression ring designs will have an essentially rectangular cross section or a keystone cross section. The periphery will then have either a barrel profile (top compression rings) or a taper napier form (second compression rings). There are some taper faced top rings and on some old engines simple plain faced rings were used.

Oil control rings typically are of three types: (1) single piece cast iron, (2) helical spring backed cast iron or steel, or (3) multipiece steel. The spring backed oil rings and the cast iron oil rings have essentially the same range of peripheral forms which consist of two scraping lands of various detailed form. The multipiece oil control rings usually consist of two rails or segments (these are thin steel rings) with a spacer expander spring which keeps the two rails apart and provides the radial load.

[edit] Wear due to ring load on the bore

Piston rings are subject to wear as they move up and down the cylinder bore due to their own inherent load and due to the gas load acting on the ring. To minimize this, they are made of wear-resistant materials, such as cast iron and steel, and are coated or treated to enhance the wear resistance. Two-stroke port design is critical to ring life. Newer modern motorcycle manufacturers have many single function but serrated ports to retain the ring. Typically, top ring and oil control rings will be coated with Chromium [2] , or Nitrided [5] , possibly plasma sprayed[6] or have a PVD (physical vapour deposit)[3]ceramic coating. For enhanced scuff resistance and further improved wear, most modern diesel engines have top rings coated with a modified chromium coating known as CKS[4] or GDC[7], a patent coating from Goetze which has aluminium oxide or diamond particles respectively included in the chrome surface. The lower oil control ring is designed to leave a lubricating oil film, a few micrometres thick on the bore, as the piston descends. Three piece oil rings, i.e. with two rails and one spacer, are used for four-stroke gasoline engines.

[edit] Fitting new piston rings

When fitting new piston rings, or breaking them in within an engine, the end gap is a crucial measurement. In order that a ring may be fitted into the "grooves" of the piston, it is not continuous but is broken at one point on its circumference. The ring gap may be checked by putting the ring into the bore/liner (squared to bore) and measuring with a feeler gauge. End gap should be within recommended limits for size of bore and intended "load" of engine. Metals expand with a rise in temperature, so too small a gap may result in overlapping or bending when used under hot running conditions (racing, heavy loads, towing), and even at normal temperatures, a small ring gap may lead to ring gap closure, ring breakage, bore damage and possible seizure of the piston. Too large a gap may give unacceptable compression and levels of blow-by gasses or oil consumption. When being measured in a used bore it may indicate excessive bore wear or ring wear.(Radial wear on ring face reduces thickness of used/worn ring (face wear in bore) essentially decreasing face circumference of ring and thereby increasing size of ring end gap.)

When fitting new rings to a used engine, special "ridge dodger" rings are sometimes used for the top compression ring, to improve compression and oil consumption without reboring the cylinder. These have a small step of iron removed from the top section to avoid making contact with any wear ridge at the top of the cylinder, which could break a conventional ring. Generally, these are not recommended as they are probably not required and may give inferior oil consumption. A more acceptable method is to remove the wear ridge with a "ridge reamer" tool before lightly honing the bore to accept new rings. In fact if the "ridge " is measured it will generally be apparent it is not really a ridge but a relatively local hollow caused by the top ring near the ring reversal point. The upper edge of this hollow will take the form or a "ramp" about 2mm long from the point of maximum wear to the point of zero wear. In this case there is not actually any ridge to hit, so light honing may be all that is required.

PistonA piston is a component of reciprocating engines, pumps and gas compressors. It is located in a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from expanding gas in the cylinder to the crankshaft via a piston rod and/or connecting rod. In a pump, the function is reversed and force is transferred from the crankshaft to the piston for the purpose of compressing or ejecting the fluid in the cylinder. In some engines, the piston also acts as a valve by covering and uncovering ports in the cylinder wall.

[edit] Piston enginesMain article: Reciprocating engine

[edit] Internal combustion engines

There are two ways that an internal combustion piston engine can transform combustion into motive power: the two-stroke cycle and the four-stroke cycle. A single-cylinder two-stroke engine produces power every crankshaft revolution, while a single-cylinder four-stroke engine produces power once every two revolutions. Older designs of small two-stroke engines produced more pollution than four-stroke engines. However, modern two-stroke designs, like the Vespa ET2 Injection utilise fuel-injection and are as clean as four-strokes. Large diesel two-stroke engines, as used in ships and locomotives, have always used fuel-injection and produce low emissions. One of the biggest internal combustion engines in the world, the Wärtsilä-Sulzer RTA96-C is a two-stroke; it is bigger than most two-storey houses, has pistons nearly 1 metre in diameter and is one of the most efficient mobile engines in existence. In theory, a four-stroke engine has to be larger than a two-stroke engine to produce an equivalent amount of power. Two-stroke engines are becoming less common in developed countries these days, mainly due to manufacturer reluctance to invest in reducing two-stroke emissions. Traditionally, two-stroke engines were reputed to need more maintenance (despite exceptions like the Ricardo Dolphin engine, and the Twingle engines of the Trojan car and the Puch 250 motorcycle). Even though the simplest two-stroke engines have fewer moving parts, they could wear out faster than four-stroke engines. However fuel-injected two-strokes achieve better engine lubrication, also cooling and reliability should improve considerably.

Gallery

A piston and its CAD drawing of

Large pistons (over Simplified piston

connecting rod. crankshaft and pistons.0.5 m incl. connecting rod).

animation.

Two-stroke engine with a tuned expansion pipe

[edit] Steam engines

Steam engines are usually double-acting (i.e. steam pressure acts alternately on each side of the piston) and the admission and release of steam is controlled by slide valves, piston valves or poppet valves.

[edit] Air cannons

The lists in this article may contain items that are not notable, encyclopedic, or helpful. Please help out by removing such elements and incorporating appropriate items into the main body of the article. (November 2008)

There are two special type of pistons used in air cannons: close tolerance piston and double piston. While in close tolerance piston, O-rings are used as valve but in double piston, O-rings are not used.

There are some features of close tolerance piston mentioned below:

1. Piston can swell and stick. 2. Fits tightly in the cylinder. 3. Tight tolerance fit. 4. Properties alter due to atmospheric change. 5. Backlash may such,some of the bin material into the valve which also can cause

the piston to stick.

Common features of double piston:

1. Cannot swell and stick. 2. Fits loosely in the cylinder. 3. No tight tolerance fit. 4. Properties are not altered due to atmospheric change. 5. Two depression on the top of the piston so make enough clearance. 6. Even if foreign material enters the valve,the double piston does not stick.

[edit] Drawbacks

This section may require cleanup to meet Wikipedia's quality standards. Please improve this section if you can. (March 2009)

Since the piston is the main reciprocating part of an engine, its movement creates an imbalance. This imbalance generally manifests itself as a vibration, which causes the engine to be perceivably harsh. The friction between the walls of the cylinder and the piston rings eventually results in wear, reducing the effective life of the mechanism.

The sound generated by a reciprocating engine can be intolerable and as a result, many reciprocating engines rely on heavy noise suppression equipment to diminish droning and loudness. To transmit the energy of the piston to the crank, the piston is connected to a connecting rod which is in turn connected to the crank. Because the linear movement of the piston must be converted to a rotational movement of the crank, mechanical loss is experienced as a consequence. Overall, this leads to a decrease in the overall efficiency of the combustion process. The motion of the crank shaft is not smooth, since energy supplied by the piston is not continuous and it is impulsive in nature. To address this, manufacturers fit heavy flywheels which supply constant inertia to the crank. Balance shafts are also fitted to some engines, and diminish the instability generated by the pistons movement. To supply the fuel and remove the exhaust fumes from the cylinder there is a need for valves and camshafts. During opening and closing of the valves, mechanical noise and vibrations may be encountered. A two-stroke engine does not require valves, meaning it doesn't need a camshaft, making these engines faster and more powerful.