2-stroke engine slide presentation – october 2012

8/12/2019 2-Stroke Engine Slide Presentation October 2012

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Paper Number 2012-36-0122

LIQUID FUEL VAPORIZATION PROCESS

BUILT INSIDE 2-STROKE PISTON ENGINES

Horacio A. TruccoACENT Laboratories

Bohemia, New York 11716, USA

[email protected]

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ABSTRACT

The process takes place inside a vaporization chamber integrated within a piston

Vaporization chamber inlet/outlet is located on the piston skirt

Is sealed by the cylinder wall for two portion of the cycle

Injected liquid fuel evaporates inside vaporization chamber

Evaporated fuel is transferred into cylinder to form a quasi homogenous mixture

Combustion is triggered by compression-ignition of a pilot fuel spray

Combustion products enter vaporization chamber via a transfer port

Fuel injected into vaporization chamber during expansion phase of a prior cycle Fuel droplets absorb heat from entrapped combustion products

At 6,000 RPM there is sufficient residence time to evaporate and superheat diesel

fuel droplets smaller than 200 microns

Concept reduces untreated emission levels of NOx, CO, soot and UH comparing to

SI, CI or HCCI engines. Improvement in engine fuel economy is expected

Fuel does not need to be rated for octane or cetane number

Effectively utilization of coal-water-slurry fuels

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INTRODUCTION

The concept shares similarities with both the hot bulb engine and the CI engine

Primary liquid fuel is injected into a small piston chamber during a preceding cycle

expansion stroke before piston reaches BDC

Its thermodynamic cycle develops two simultaneous pressure versus crank angle

diagrams

Its combustion process is comparable to the HCCI case

Less costly and simpler after treatment devices will suffice to comply with emission

standard regulations

Less costly and simpler fuel injection system is acceptable

The concept aims to conserve energy and to better protect the environment

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CONCEPT DESCRIPTION -1

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CONCEPT DESCRIPTION - 2

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CONCEPT DESCRIPTION - 3

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VAPORIZATION PROCESS -1

Initial vaporization chamber 800 K

Fuel injected at 1 atmosphere

Gasoline Diesel Methanol Ethanol Kerosene Fuel Oil

#6

JP 8

LHV, Btu/lb 18,676 18,394 8,637 11,585 18,540 18,500 18,700Heat of Vaporization, Btu/lb 150 100 506 396 110 95 129

Liquid specific Heat, Btu/lb F 0.48 0.43 0.60 0.57 0.46 0.45 0.53

Saturation Temperature, K 325 480 413 416 520 533 488

Liquid Heating from 300 K, Btu/lb 21 139 122 119 182 116* 179

Superheating for a Tsh=50

K=90 F and cp=0.35, Btu/lb

31 31 31 31 31 31 31

TH, Btu/lb 202 270 659 546 323 242 339

LHV /TH 92 68 13 21 57 76 55

Chamber temperature drop Tch, F 765 486 606 601 414 390 471

Stoichiometric air-fuel ratio 14.7 14.6 6.5 9.0 15.6 14.4 15.4

Vrel=VChamber/VCylinder 4.2 % 8.7 % 27.8 % 23.2 % 11.5 % 10 % 10.6 %

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VAPORIZATION PROCESS - 2

Residence time available for vaporization represents up to 180 of crankshaft

rotation

At 6,000 RPM corresponds to 5.1 milliseconds

Consider 700 K and 10 atmosphere entrapped combustion products

Diesel or gasoline fuel droplet no larger than 200 microns injected at U=50 m/s will

completely vaporize

That is a relatively coarse fuel spray

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Fraction of evaporating fuel droplets may impinge vaporization chamber inner wall

developing a liquid film or floating over the wall (Leidenfrost effect)

Oscillating inertial forces affect heat transfer rate

An average size automobile may incorporate a 7.5 centimeter long vaporization

chamber

A U=50 m/s spray hits the vaporization chamber bottom in 1.5 milliseconds

Droplet larger than 100 microns hit the inner wall

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CHARGE FORMATION

Vaporized/superheated fuel species are transferred into the cylinder midway

through the compression stroke, see Figure 3

Fuel species mix with a fresh air charge developing into a quasi homogeneous fuel

lean charge

Charge is laden with inert combustion gases (CO2, H2O, CO, etc.) representing an

inherited internal combustion gas recirculation (ICGR) process

This fact plays an important effect on NOxreduction

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COMBUSTION PROCCESS - 1

A pilot fuel injected into the combustion chamber creates a multiple-jet spray

After an ignition delay each pilot fuel jet ignites as occurs inside a CI engine

Multiple ignition sources simultaneously develop inside the vitiated leanhomogeneous charge

Subsequent combustion is carried out in a manner resembling the HCCI process

Ignition is not controlled by chemical kinetics as occurs within HCCI engines

Ignition is controlled by pilot fuel injection timing and a quasi-spatial heat source

distribution

Because of that the primary liquid fuel is not required to be rated for octane

number

Each pilot fuel jet initially burns as a diffusion flame reacting at near stoichiometric

conditions producing significant amounts of discrete NOx

Localized NOxformation is reduced by inducing turbulence, the pilot fuel burns

partially premixed thus the local flame temperature is reduced

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Since combustible mixture is vitiated by ICGR, the heat release rate should be much

slower than that for HCCI reducing combustion-generated noise

This engine should exhibit a single heat release rate peak preventing diesel knock

The primary liquid fuel is not required to be rated for cetane number

Tolerates gasoline and diesel fuel without additive

Accepts low-cost petroleum derived fuels, biodiesel, bio-alcohol, vegetable oils and

biomass fuels

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In-cylinder swirl enhances mixing during pilot fuel combustion from points C to

D

Uniflow scavenged 2-stroke engines are able to generate intense in-cylinder swirlmotion that further reduce localized NOxformation by pilot fuel spray jets

In-cylinder swirl helps to attain a fully homogeneous charge prior to pilot fuel

injection

Described combustion process was qualitative, there is need to acquire detailed

knowledge via experiments and computational simulation

Analytical evaluation requires state-of-the-art computational modeling and

simulation

Three separate modeling efforts are required:

(1) vaporization process, spray wall impingement heat transfer, fuel distillation,

possible chemical breakdown, heat losses into chamberand cylinderwalls as well

as possible fuel oxidation.

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COMBUSTION PROCCESS 8


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(2) fluid dynamic modelingfor the transfering into cylinder of vitiated vaporized

fuel species and subsequent formation of a homogeneous charge

(3) fluid dynamic and chemistry formulationfor the initial pilot fuel jet mass

diffusion flame throughout the final burn of the well-stirred vitiated lean

homogeneous charge

Experimental measurements are indispensable to fully understand the process and

to eventually fine tune any prototype

Engine cycle permits utilization of diesel-like or higher compression ratios

increasing efficiency when compared to SI engines

Engine can supply a wide power range because there are no flammability limit

constraints on a vitiated lean homogeneous charge spatially ignited by multiple

pilot fuel injection jets

Engine operates un-throttled Power output is controlled by the amount of primary fuel injected into vaporization

chamber

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In-cylinder average air/fuel ratio may vary from very lean to the highest

equivalence ratio limited by acceptable NOxformation

An important advantage when comparing this combustion process to the HCCI case

Combustion initiation is not controlled by chemical kinetics as in the HCCI case, but

by pilot fuel injection jets. Multi point pilot fuel injection allows burning within a

very wide equivalence ratio range while producing stable combustion

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COLD STARTING


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COLD STARTING

Cold starting is accomplished in a CI engine mode

Only pilot fuel injection is supplied during warm-up

For low grade fuels (such as fuel oil #6 that requires preheating to attain pumping

ability) the primary fuel injector body can be briefly pre-heated by electric means

so that the fuel spray is injected pre-heated to attain partial flash atomization

A secondary primary fuel with high volatility will also assist starting when utilizing

low grade fuels

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GENERAL APPLICATION TO PISTON ENGINES


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GENERAL APPLICATION TO PISTON ENGINES

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UTILIZATON OF SPECIAL FUELS 1


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UTILIZATON OF SPECIAL FUELS - 1

Large bore-low-speed engines utilizing residual fuel oils can benefit from this

proposed process

Improves emission and thermal efficiency and increase power density by running at

higher speed

A medium speed engine at 600 RPM will make available 51 milliseconds ofresidence time

Entrapping 700 K combustion products and injecting at U=25 m/s will evaporate a

200 micron #6 fuel droplets in 8 millisecond.

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Global reserve of crude petroleum may be exhausted during the next 100 years

Global coal reserves should still remain available for about another 300 years

We must utilize coal-water-slurry fuel (CWF) in large bore-low-speed and mediumsize ICEs

That would delay the exhaustion of crude reserves and prepare technology, fuel

supply logistics and commercial market structure to feed a large percentage of

future ICEs with coal-derived replacement fuels

Efficient utilization of CWFs in diesel engines has been extensively demonstrated byproof-of-concept R&D as well as commercial pilot projects

Utilization of CWF in direct injection diesel engines is highly efficient with low

emissions characteristics

CWF causes excessive engine wear that is more accentuated with smaller bore

engines The need to solve this acute durability hurdle is mandatory prior to commercial

acceptance of ICEs operating with CWF

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That wear mainly centers on CWF injector orifices

Atomization of CWF is more difficult than diesel fuel, a higher injection pressure is

required to attain faster injection velocity through the nozzle orifice That implies smaller injection orifices for the same fuel injection rate

The abrasive erosion of CWF at high injection velocity reduces useful life of

injectors made from conventional materials to about one hour

Injectors orifice inserts made from sapphire or ceramic survive up to 100 hours

CWF spray should deliver droplet ranging from 20 to 40 microns SMD to attain

efficient burning

That fine spray demands a CWF velocity through injector orifices ranging from 250

to 400 m/s

The proposed process should solve the above injector wear issue because acceptscoarse droplet size, larger orifices and lower injection velocities that prolong

injector durability

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Initial vaporization chamber 800 KCoal

Water at

10 atm

CWF 60

wt % coal

LHV, Btu/lb 9,300 - 5,580

Heat of Vaporization, Btu/lb - 865 346

Specific Heat, Btu/lb F 0.42 1.0 0.625

Saturation Temperature, K - 458 458

Heating from 400 K to Saturation

Temperature, Btu/lb

- - 36

TH, Btu/lb - 865 382

LHV /TH - - 14.6

Chamber temperature drop Tch, F - - 975Stoichiometric air-fuel ratio 11.4 - 6.84

Vrel=VChamber/VCylinder - - 13 %28



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UTILIZATON OF SPECIAL FUELS - 7 Engine running at 300 RPM will make available 102 milliseconds of residence time

A 200 micron CWF droplet injected into 700 K entrapped combustion products at

U=25 m/s could evaporate its water content in 17 milliseconds

The remaining 85 milliseconds could be utilized to thermally treat the dry coalparticles.

Intuitively, one may assume that such CWF injector is very durable. Experimental

data will confirm an injector useful lifetime

Largest cylinder bore today reaches 96 centimeters, found on engines used by large

ocean-going vessels.

A vaporization chamber 75 centimeters long can be accommodated inside such a

piston

A spray injecting at 25 m/s will hit that vaporization chamber bottom in 30

milliseconds

After interstitial water vaporization the dried coal particles could reach

devolatilization and fragmentation and possible chemical breakdown prior to

entering the combustion chamber30



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A dried coal particle still entraps water in its peripheral pore network

At 10 atm, water saturation is 458 K, a sufficiently large vaporization chamber will

cause the entrapped water to increase its pressure causing an initial fragmentationof the coal particle outer shell

Subsequently, the coal particle fragmentation continues during devolatilization due

to a pressure build up of the volatile matter entrapped

Should this process be realized, less particulate matter would result from the

issuing combustion

Ash content percent cannot be reduced so consequently ultra-clean CWF is

required

The process may prevent undesirable ash particle agglomeration

The typical wear on cylinder wall, piston land and piston rings should be mitigated

in comparison to direct injection of CWF into diesel engines

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SUMMARY - 1


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SUMMARY - 1

The HCCI engine is projected to have attractive low emission levels and high fuel

economy

The HCCI engine confronts five practical challenges that must overcome before it

can be widely used

The proposed combustion process should allow elimination of these five practical

challenges while retaining low emission levels of NOx and soot and the high fuel

economy characterizing the HCCI engine

The five HCCI engine challenges are: (1) Controlling combustion auto ignition timing. Proposed process eliminates this

challenge by utilizing reliable multiple-jet fuel injection ignition source

(2) Expanding output capability, now limited to about 0.4, is structurally limited

by rapid combustion pressure rise. The process proposed safely operate at higher

because its heat release rate is slower than the HCCI case (see Figure 8)

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SUMMARY 2


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SUMMARY - 2

(3) The HCCI engine noise is a disadvantage caused by explosive type of auto

ignition combustion. At high load, the noise level can be damaging to human

hearing. The process proposed should generate lower noise levels because heat

release rate is slower than the HCCI engine (see Figure 8)

(4) It is difficult to cold start the HCCI engine, preheating of the intake charge is

usually required. An engine with the proposed process starts rapidly in a regular CI

mode via a pilot fuel injection system

(5) High level of unburned hydrocarbons and CO. Premixed charge that reaches

crevices and the cooler boundary layers on the engine walls is unable to burn. The

proposed engine fuel enters in contact with the upper-half of the cylinder where

the crevices and boundary layer are warmer. In-cylinder swirl motion refreshes the

boundary layer entraining warm fuel species. Vaporized fuel near the walls is

relatively hotter than the droplets in the HCCI charge thus should be able to burn

during the well-stirred final combustion phase

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CONCLUSIONS


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CONCLUSIONS

The vaporization and vitiated-lean-homogeneous-charge combustion process

presented offers potential for substantial reduction of raw emission contaminants

and optimal fuel economy when compared to contemporary piston ICEs

Required fuel injection system is simpler, robust and less costly than thosecurrently utilized by ICEs

After-treatment of its raw exhaust requires simpler, robust and less costly devices

than those currently utilized by ICEs

This process can efficiently employ gasoline or diesel fuels without additives or

blends

As well as low-cost petroleum derived fuel, biodiesel, bio-alcohol and vegetable oil

The unavoidable exhaustion of petroleum derived fuels within a century could

reduce the utilization of contemporary ICEs since only alternative non-petroleum

liquid fuels would be available

However, the process presented should permit some of those ICEs to continue

delivering clean and efficient energy by fueling them with ultra-clean coal derived

CWF34

THANK YOU! MUITO OBRIGADO!


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THANK YOU! MUITO OBRIGADO!

For more information contact

Horacio A. Trucco

ACENT Laboratories

80 Orville Drive, Suite 100

Bohemia, New York, 11716, USA

Telephone: +1-631-801- 2616

Skype: horacio.a.trucco

[email protected]

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mailto:[email protected]:[email protected]

2-stroke engine slide presentation – october 2012

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