A Technical Review of the Future Internal Combustion Engines

Semin, Rosli A. Bakar Faculty of Mechanical Engineering, University Malaysia Pahang

AbstractThe internal combustion engine (ICE) is already 100 years old, no better prime mover for vehicle has so far been invented for common use. The continuously rising prices of hydrocarbon fuels and the needs of environmental protection have determined the development trends of combustion systems and account for the preference for the compression-ignition engine over the conventional spark-ignition engine for driving vehicles. Intense research is now in progress on the use of gaseous fuels and methanol, but this would necessitate certain adaptive charges in the combustion systems of the engines operated so far. There exist numerous and diversified designs of combustion systems but all are based on the same principles. In the century that has elapsed since it was first introduced, the internal combustion engine in its various forms has come to dominate the transport field and, through the motor-car, has conferred on mankind a degree of individual mobility never previously known. The depletion of oil reserves, and rising prices for hydrocarbon fuels, inevitably pose important questions concerning the future of this source of motive power. This article reviews the general future of such engines and the way in which they are being adapted to changing circumstances.

Keywords : Internal combustion engine, the development trends, diversified design

1. Introduction

In 1976, a hundred years had passed since Nicolas August Otto constructed a four-stroke gas-fuelled internal combustion engine and patented its cycle in 1876 (Patent DRP No.532,1876). In spite of the fact that the power output of the engine was only approximately 2.2kW (3 hp) and ignition was started by hot gases, it was a precursor of modern Internal Combustion Engine (ICE) because the mixture was compressed and burned in a single cylinder, the machine also had other interesting design features. It can be said without exaggeration that this invention revolutionized the world. After ten years (1886) an ICE was installed in a motorcar, and after twenty seven years (1903) was installed in an aircraft. In 1974 some 35 million motor vehicles driven by engines based on the Otto cycle were produced.

In 1893, Rudolf Diesel constructed an experimental compression-ignition engine and patented the relevant cycle in 1892 (Patent DRP N0,67207, 1892). Four years later, a working version of the engine had an efficiency 0f 26% at a power output of approximately 14.7kW (20 hp). This although the engine was not originally applied for driving a vehicle, was the second fundamental invention in the history of the automobile. In 1976, the total output by the West European countries only was 5,200,000 compression-ignition engines.

Although the gas turbine was invented by John Barber in 1791, it was not until 1939 that is became a fully efficient driving engine. Its subsequent rapid development was due to its being applied in air-craft engineering. Other heat engines invented later then Internal Combustion reciprocating engine were not

suitable for wide and common use in vehicles or aircraft. The regular development of ICE changes direction in answer to changing requirement. In the 1970, the two most important problems determining the development trends of engines, and in particular, their combustion systems, were : environmental protection against emission and noise, and shortage of hydrocarbon fuels. The brief comparison of a variety of engine undertaken in what follows principally concerns specific fuel consumption, toxic properties of emissions, and other technical and economic parameters. It should be borne in mind that although the reciprocating piston engine is complex and far from perfect, it has fewer shortcomings than other heat engines.

2. Internal Combustion Engines

The internal combustion engine is a heat engine in which the burning of a fuel occurs in a confined space called a combustion chamber. This exothermic reaction of a fuel with an oxidizer creates gases of high temperature and pressure, which are permitted to expand. Hardenberg [6] defining feature of an internal combustion engine is that useful work is performed by the expanding hot gases acting directly to cause movement, for example by acting on pistons, rotors, or even by pressing on and moving the entire engine itself. This contrasts with external combustion engines such as steam engines which use the combustion process to heat a separate working fluid, typically water or steam, which then in turn does work, for example by pressing on a steam actuated piston. The term Internal Combustion Engine (ICE) is almost always used to refer specifically to reciprocating engines, Wankel engines and similar designs in which combustion is intermittent. However, continuous combustion engines, such as Jet

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engines, most rockets and many gas turbines are also internal combustion engines.

Figure 1. Internal combustion engine [8]

The most common fuels in use today are made up of hydrocarbons and are derived from petroleum. These include the fuels known as diesel, gasoline and liquified petroleum gas. Most internal combustion engines designed for gasoline can run on natural gas or liquified petroleum gases without modifications except for the fuel delivery components. Liquid and gaseous biofuels, such as Ethanol can also be used. Some can run on Hydrogen; however, this can be dangerous. Hydrogen burns with a colorless flame, and modifications to the cylinder block, cylinder head, and head gasket are required to seal in the flame front. Experimentation at Southwest Research Institute showed that without such modifications flame leaks from the exhaust manifolds were common. Since the flame was colorless, it was not visible to the naked eye. An invisible flame is more dangerous than a visible flame, since one cannot take into account what cannot be seen, and operator injury was regarded as a definite danger. However BMW has recently designed a 12-cylinder Hydrogen powered car, and the company has stated that it plans to market the vehicle. All internal combustion engines must have a means of ignition to promote combustion. Most engines use either an electrical or a compression heating ignition system. Electrical ignition systems generally rely on a lead-acid battery and an induction coil to provide a high voltage electrical spark to ignite the air-fuel mix in the engine's cylinders. This battery can be recharged during operation using an alternator driven by the engine. Compression heating ignition systems, such as diesel engines and HCCI engines, rely on the heat created in the air by compression in the engine's cylinders to ignite the fuel. Once successfully ignited and burnt, the combustion products, hot gases, have more available energy than the original compressed fuel/air mixture (which had higher chemical energy). The available energy is manifested as high temperature and pressure which can be translated into work by the

engine. In a reciprocating engine, the high pressure product gases inside the cylinders drive the engine's pistons. Once the available energy has been removed the remaining hot gases are vented (often by opening a valve or exposing the exhaust outlet) and this allows the piston to return to its previous position (Top Dead Center - TDC). The piston can then proceed to the next phase of its cycle, which varies between engines. Any heat not translated into work is a waste product and is removed from the engine either by an air or liquid cooling system. The parts of an engine vary depending on the engine's type. For a four-stroke engine, key parts of the engine include the crankshaft, one or more camshafts and valves. For a two-stroke engine, there may simply be an exhaust outlet and fuel inlet instead of a valve system. In both types of engines, there are one or more cylinders and for each cylinder there is a spark plug , a piston and a crank . A single sweep of the cylinder by the piston in an upward or downward motion is known as a stroke and the downward stroke that occurs directly after the air-fuel mix in the cylinder is ignited is known as a power stroke. A Wankel engine has a triangular rotor that orbits in an epitrochoidal chamber around an eccentric shaft. The four phases of operation (intake, compression, power, exhaust) take place in separate locations, instead of one single location as in a reciprocating engine. A Bourke Engine uses a pair of pistons integrated to a Scotch Yoke that transmits reciprocating force through a specially designed bearing assembly to turn a crank mechanism. Intake, compression, power, and exhaust all occur in each stroke of this yoke.

2.1. Petrol engines

The term gasoline engine / spark-ignition engine is normally used to refer to internal combustion engines where the fuel-air mixture is ignited with a spark. Spark-ignition engines can be either two-stroke or four-stroke, and are commonly referred to as "gasoline engines" in US English and "petrol engines" in British English. However, these terms are not preferred, since spark-ignition engines can (and increasingly are) run on fuels other than gasoline, such as methanol, ethanol, CNG, hydrogen, and nitromethane. A four-stroke spark-ignition engine is an Otto cycle engine, Hardenberg [6]. The cycle begins at top dead centre (TDC), when the piston is furthest away from the crankshaft. On the first stroke (intake) of the piston, a mixture of fuel and air is drawn into the cylinder through the intake (inlet) port. The intake (inlet) valve (or valves) then close(s) and the following stroke (compression) compresses the fuel-air mixture. The air-fuel mixture is then ignited, usually by a spark plug for a gasoline or Otto cycle engine or by the heat and pressure of compression for a Diesel cycle of compression ignition engine, at approximately the top of the compression stroke. The resulting expansion of burning gases then forces the piston

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downward for the third stroke (power) and the fourth and final stroke (exhaust) evacuates the spent exhaust gases from the cylinder past the then-open exhaust valve or valves, through the exhaust port.

Figure 2. Petrol engine

2.2. Diesel Engines

The Diesel Engine is a type of internal combustion engine; more specifically, it is a compression ignition engine, in which the fuel is ignited solely by the high temperature created by compression of the air-fuel mixture, rather than by a separate source of ignition, such as a spark plug, as is the case in the gasoline engine. The engine operates using the diesel cycle. In very cold weather, diesel fuel thickens and increases in viscosity and forms wax crystals or a gel. This can make it difficult for the fuel injector to get fuel into the cylinder in an effective manner, making cold weather starts difficult at times, though recent advances in diesel fuel technology have made these difficulties rare. A commonly applied advance is to electrically heat the fuel filter and fuel lines. Other engines utilize small electric heaters called glow plugs inside the cylinder to warm the cylinders prior to starting. A small number use resistive grid heaters in the intake manifold to warm the inlet air until the engine reaches operating temperature. Engine block heaters (electric resistive heaters in the engine block) plugged into the utility grid are often used when an engine is shut down for extended periods (more than an hour) in cold weather to reduce startup time and engine wear. A vital component of older diesel engine systems was the governor, which limited the speed of the engine by controlling the rate of fuel delivery. Unlike a petrol (gasoline) engine, the incoming air is not throttled, so the engine would overspeed if this was not done. Older injection systems were driven by a gear system from the engine (and thus supplied fuel only linearly with engine speed

Figure 3. Diesel engine

2.3. Wankel Rotary Engines

Wankel was invented by German engineer Felix Wankel. Wankel first conceived his rotary engine in 1954 (DKM 54) and the KKM 57 (the Wankel rotary engine) in the year 1957. Considerable effort went into designing rotary engines in the 1950s and 1960s. They were of particular interest because they were smooth and very quiet running, and because of the reliability resulting from their simplicity. The Wankel rotary engine is a type of internal combustion engine, which uses a rotor instead of reciprocating pistons. The internal combustion engine is a heat engine in which the burning of a fuel occurs in a confined space called a combustion chamber. This exothermic reaction of a fuel with an oxidizer creates gases of high temperature and pressure, which are permitted to expand.

Figure 4. Wankel Engine in Deutsches Museum Munich, Germany [8]

The defining feature of an internal combustion engine is that useful work is performed by the expanding hot gases acting directly to cause movement, for example by acting on pistons, rotors, or even by pressing on and moving the entire engine itself. This design promises smooth high-rpm power from a compact, lightweight engine; however, Wankel engines are criticized for poor fuel efficiency and

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exhaust emissions. Since its introduction in the NSU Motorenwerke AG (NSU) and Mazda cars of the 1960s, the engine has been commonly referred to as the rotary engine, a name which has also been applied to several completely different engine designs.

2.4. Gas Turbine

A gas turbine, also called a combustion turbine, is a rotary engine that extracts energy from a flow of combustion gas. It has an upstream compressor coupled to a downstream turbine, and a combustion chamber in-between. (Gas turbine may also refer to just the turbine element.) Energy is released when air is mixed with fuel and ignited in the combustor. The resulting gasses are directed over the turbine's blades, spinning the turbine and powering the compressor, and finally is passed through a nozzle, generating additional thrust by accelerating the hot exhaust gases by expansion back to atmospheric pressure. Energy is extracted in the form of shaft power, compressed air and thrust, in any combination, and used to power aircraft, trains, ships, generators, and even tanks. Industrial gas turbines range in size from truck-mounted mobile plants to enormous, complex systems. The power turbines in the largest industrial gas turbines operate at 3,000 or 3,600 rpm to match the AC power grid frequency and to avoid the need for a reduction gearbox. Such engines require a dedicated building. They can be particularly efficient — up to 60% — when waste heat from the gas turbine is recovered by a conventional steam turbine in a combined cycle configuration.

Figure 5. Gas turbine

They can also be run in a cogeneration configuration: the exhaust is used for space or water heating, or drives an absorption chiller for cooling or refrigeration; cogeneration can be over 90% efficient. Simple cycle gas turbines in the power industry require smaller capital investment than combined cycle gas, coal or nuclear plants and can be designed to generate small or

large amounts of power. Also, the actual construction process can take as little as several weeks to a few months, compared to years for baseload plants. Their other main advantage is the ability to be turned on and off within minutes, supplying power during peak demand. Large simple cycle gas turbines may produce several hundred megawatts of power and approach 40% thermal efficiency.

3. Comparison of Internal Combustion Engines

3.1. Otto and Diesel EnginesKowalewicz [1] said that the Otto cycle is less efficient

than the Diesel, since the spark-ignition engine consumes more fuel than the compression-ignition engine. The former is characterized by higher weight and volumetric power factors, but is very sensitive to fuel properties and requires higher octane numbers. The Otto cycle engine has developed in two directions. The traditional carburetor fuel supply system is replaced by an injection system to obtain higher acceleration. Higher permissible instantaneous overloading, higher economic factors of performance and lower emissions. The conventional ignition system is replaced by electronic circuits. The other trend of development is oriented toward reducing emission toxicity by applying the principle of stratified chage. This principle can be implemented in various ways. Stratified charge engines will be more and more widely used, so that in 1985 it will presumably replace conventional engines equipped with after-burning catalytic reactor. The stratific-charge engine will in the future be very competitive with the diesel engine. Inherent in the standard spark-ignition carburetor engine are certain very disadvantageous features such as high fuel consumption and high emission toxicity. For this reason, it will be replaced in self-propelled vehicles by the diesel high-speed engine which is less expensive in operation and less toxic. For the same reasons, two-stroke engines have very narrow applications. An interesting forecasting analysis concerning selection of an engine for passenger cars was carried out. The choice lays mainly between the four stroke carburetor and compression engine. It was found that, mounted on an automobile of given weight, a compression ignition engine consumes from 25 to 30% less fuel than carburetor engine. It follow from this experiment that not only is the diesel engine less costly in use but also that is emits less toxic pollutants per kilometer. The development of four stroke compression-ignition engines has been stimulated by economic and environmental protection requirement and has taken the following directions.

Diesel engines of low and medium power output are applied mainly for propelling vehicles (passenger vehicles, short distance pick-ups and similar types) and tend to meet the requirements of environmental protection (low emission toxicity and slight noise) event at the expense of greater fuel consumption, of importance here is the

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tendency to high power factors per engine volume but without supercharging. In these engines, the combustion system is equipped with a divided chamber. On the other hand, as regard high power out engines designed for intercity coaches and heavy trucks, the demand is for the lowest possible running costs, that is, low fuel consumption and long operational life. These engines are mostly fitted with direct fuel injection and as compared with those used in the 1950-1960, their combustion systems have been modernized. Very often they are supercharged.

At least in European built engines, the problem of emission toxicity is not very important. The farm and industrial engines (with the exception of those employed in mines and interiors) should meet similar requirements. Attemps are being mode to economize fuel by reducing power, particularly in passenger cars (American-built cars have considerable surplus power output). Legal regulations covering permissible toxic emission from diesel engines were introduced in 1973 in U.S.A and in 1975 in Japan. In Western in Europe the legal regulations introduced in 1971 covered only spark-ignition engines limits on CO and HC but they are to be extended also to diesel engines.

Clearly, economic and environmental protection reasons are insignificant in certain applications. These are engines used in racing and sports motor-cycles and cars and propelling aircraft. In this applications, the most vital are power factors for engine volume and weight. Spark-ignition engines, achieving volumetric power factors higher than 100 kW/dm3, have no competition in this field. Two-stroke engines have even greater power factors and are still use on racing motor cycles, but in aircraft engineering they are virtually inapplicable because they consume more fuel which thus imposes additional fligt load.

3.2. Wankel Rotary EnginesThe Wankel petrol engine operating in the Otto

cycle, has advantages such as high weight power factor, smooth running and the possibility of using fuels of low octane number. However, its development has come to a standstill as a result of its consuming more fuel than other types of engines and its emission being highly toxic of hydrocarbons and carbon oxide. The Wankel engine is also more costly since only little experience has so far been acquired in relevant production processes. Wankel automobile engines was manufactured by the Mazda and NSA companies but only on small scale. Citroen ceased production of them in 1974. Because the Wankel engine with a Diesel cycle is difficult in design and production processes, prospects for its future development are break.

3.3. Gas Turbine

The gas turbine used for driving vehicles which are no competitive with the piston engine is in the range of low and medium power because its cyclic efficiency is poorer and consequently its specific fuel consumption is high. However, increasing demand for high driving power in heavy vehicles of 6 to 7.5 kW/t (8 to 10 hp/t) may. Within the range of power above 300 kW (400 hp) where gas turbine and compression ignition engines become comparable, lead to confrontation.

At partial loading, the turbine consumes more fuel than spark and compression ignition engines, this being a major disadvantage regarding the weight power factor at ouput higher than 75kW (100 hp), the gas turbine is considerably advantageous and thus is much more suitable for special vehicles requiring a light-weight driving unit and high acceleration. In high speed aircraft also, the piston engine has been replaced by the gas turbine mainly due to its weight and volumetric power factors and small dimensions. But aircraft used for training and agricultural purpose are still propelled by piston (spark ignition) engines since they are more economic. Emission from the gas turbine are less toxic than those from the spark-ignition piston engine, the excess make them comparable with those of the diesel engine. Combustion in the gas turbine is owing to the existing conditions (continuous process, low pressure), almost perfect and complete (consequently low concentrations of CO and HC). But since the temperature and oxygen excess are high, the concentration of nitric oxide (NO) is relatively high and comparable to that of the diesel engine. Taking into account economic factors (production costs, greater fuel consumption) and the comparable toxicity of emission, it may be said in conclusion that the gas turbine cannot complete with the piston engine for power output smaller than 260 to 300 kW (350 to 400 hp).

4. Internal Combustion Engines Future Fuel

The use of non-conventional fuels in ICE is one of the development trends in view of today’s imperative demands regarding engines, such unconventional fuels may be methanol (liquid) and the following gases : methane, propane, natural gas containing methane, as well as hydrogen. The spark-ignition methanol engine feature an indicated efficiency higher than the petrol engine, in particular, with excessive air supply and consequently, lower emission toxicity. Since the hydrocarbon gases have poorer self-ignition properties than diesel oil, gases are applicable mainly in spark-ignition engines. Kowalewicz [1] said that the gas spark-ignition engine has a lower efficiency and a higher fuel consumption than the compression-ignition engine but at the same time, the concentration of its combined toxic constituents is lower. Since these engines present difficulties in operation because frequent exchange of gas-filled tank, explosion hazard-especially in the case of hydrogen, large size of the

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tank, etc. They are likely to be used on urban buses and short distance pick-ups.

Tabel 1. Fuel properties at 250C and 1 atm

Figure 9. NOx emission of hydrogen[3]

Figure 10. Thermal efficiency of hydrogen [3]

5. Internal Combustion Engine Future Technology

Of all heat engines, the ICE with a stirling cycle and efficiency equal to of the Carnot cycle is the most advantageous thermodynamically. Its curve of overall efficiency in relation to speed is flat, a feature highly desirable in vehicle driving. The power output of the stirling engine is a linear function of speed. Even at low speeds, power and efficiency are relatively high. Overall efficiency

comparable to that of conventional piston engines is obtained at high (approx. 100daN/cm2) maximum pressures of the thermal cycle. This fact and the existence of a separate combustion chamber are unfavourable to weight power factor. However, the emission has a very low concentration of carbon oxide and hydrocarbons (since, similarly to the gas turbine, the combustion process is extremely efficient). The concentration of nitric oxides is much higher than that of carbon oxide and hydrocarbons but is lower than in emissions from the diesel engine.

Stirling engine emissions conform to the requirements of the 197 Californian test CARB, that is – BS (NOx + HC) < 5 g/(hp.h) and BSCO < 25 g/(hp.h). The engine runs rather silently. The stirling engine is most suitable from the point of view of vehicle driving but a good deal remains to be done to improve its design. Since its construction costs are high, it seems unlikely that the stirling engine will within the next 20 to 30 years be competitive with conventional piston engines. The steam piston engine has far fewer prospects than the stirling engine. Although its emission is equally low, torque characteristic good and noise minimal, its poor efficiency (not above approx. 20%) is very difficult or even impossible to be raised because of specific design and operating conditions. Moreover, this engine has complex design and auxiliary systems, loa weight and volumetric power factors, and its initial costs are high. Thus, its development prospects are much less promising than those of the ICE.

Figure 6. Concept for NOx and PM reduction [4]

Figure 7. Schematic diagram of swirl chamber (multi-cylinder engine)

Although the electric direct current motor is ideal as regards environmental protection, it can in the main be used, in view of the low capacity of batteries, only for powering special vehicles. It is expected that the hybrid drive system consisting of battery-and-electric set and diesel engine-and-generator set have certain development prospects. The electric motor will not be competitive with the ICE for self-propelled vehicles until highly efficient batteries or electric cells with high capacities and /or small dimensions are developed, this is expected to be achieved by the

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year 2000. Other unconventional prime movers will not be considered.

Figure 8. Schematic diagram of swirl chamber (single-cylinder engine)

.6. Conclusion

All the internal combustion engine further considered in this paper are based a single general principle, namely the most efficient conversion of the chemical energy of fuel into work so as to obtain the highest possible power output of the engine, the lowest possible emission of toxic compounds into the atmosphere and the longest operational life of the prime mover. Combustion systems can be optimized according to three basic criteria, maximum economy in operation, maximum obtainable power output and minimum toxicity of emissions. The design of a combustion system in ICE is based on the optimal choice of the sub systems, so that they may meet the defined criteria or conditions of optimization. The number of common factors that can be optimally chosen as regards combustion processes is limited, but they can be combined in numerous ways. The most important factors are the manner of mixture formation, the kind and composition of mixture at the instant of

ignition and during the combustion process, and the manner of cylinder scavenging to remove exhaust gases. These factors determine the choice of the geometry of combustion space, the position of injector or spark-plug in space, the injection or ignition timing, the swirl and turbulence of the charge. A selected set of these parameters determines the optimal combustion system that can be designed in a variety to meet the assumed criteria of optimization.

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