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COMBINED NUMERICAL-EXPERIMENTAL STUDYOF DUAL FUEL DIESEL ENGINE

SHANS M.SM.TECH

THERMAL POWER ENGINEERING

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CONTENTS Introduction Duel fuel combustion trends Experimental study Engine main characteristics Ng composition Experimental result Diesel injector command signal Experimental rate of heat releases Experimental mass fractions of polluting species Co emission Experimental pressure cycle

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Experimental pressure cycle Engine characteristics Injected diesel oil mass profiles Computational domain and structured mesh Numerical results In-cylinder pressure cycles in fd and df mode No distributions [ppm] for different ch4 ratios at tdc Conclusions

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INTRODUCTION In this paper discuss about the effect of different fuel ratios on

the performance and emission levels of a common rail diesel engine supplied with natural gas and diesel oil

A viable solution to reduce emissions from diesel engines is represented by dual-fuel (diesel/NG) concept.

The main aspect of this experiment is to reduce the most dangerous emissions like Nox and particulate matter

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In the duel fuel operation characterized by diesel pilot injection for start combustion in a port premixed NG and air blend.

In the best condition up to 90% diesel oil can be replaced by NG but idle and low loads poor combustion quality & high HC emissions are occur

higher loads heavy knocking can damage engines An important target is that applying this technology is to

approach the same efficiency of a diesel engine, but with globally lower pollutant emissions

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DF COMPARISON METHODS In last years the dual-fuel combustion system has been

studied by many researchers but it has not yet reached a great diffusion due to the HC and CO emissions are higher at part load than the conventional diesel engine.

in this paper aims at the evaluation of the CFD potential to predict the main features of this particular engine operation.

The experimental investigations represent a tool for validating and highlighting the major problems that arise from the actual engine operation with different diesel fuel/NG ratios.

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The CFD tools predict flame propagation through the premixed methane air medium and find out the actual process happening during combustion.

This allowed them to refine the numerical study through successive steps.

Mainly to detect the most interesting benefits and the most challenging problems that can predicted by the purely numerical study when considering increasing NG/Diesel fuel ratios.

So that the combined numerical experimental study of dual-fuel diesel engines that is carried out.

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EXPERIMENTAL STUDY The experimental activity has been carried out at Istituto

Motori (CNR) on a common rail direct injection displacement turbocharged diesel engine.

The engine can operate as a normal diesel engine FD & DF In case it is fuelled by a homogeneous natural gas/air mixture that is ignited by a pilot diesel injection.

No hardware modification required so that easily switched from FD to DF

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In DF mode NG is mixed with air into the intake manifold and ignited by a pilot diesel injection like in an usual diesel engine there are many ignition points from which combustion starts and then propagates in a way similar to a SI engine.

Best operating conditions are reached at mid load Most critical conditions are at the low and high load

The mixture is homogeneous no throttle valve to control the torque output, at low load the mixture becomes too lean.

Therefore NG/air mixture does not allow any front flame propagations.

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ENGINE MAIN CHARACTERISTICSEngine 1.9 Multijet

Type 4 stroke

Number of cylinders 4

Valves /cyl 2

Bore (mm) 82

Stroke (mm) 90.4

Compression Ratio 19:1

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NG COMPOSITIONFuel properties Basic data

ρ (kg/Stdm3) .83

LHV(MJ/kg) 45.83

CH4(%vol) 85.44

Ethane (%vol) 3.38

Propane (%vol) 1.71

Buthane (%vol) .47

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EXPERIMENTAL RESULT

The electrical signal that governs the injectors operation detect the exact instants of activation of both pilot and main injections.

This should allow much more accurate calculations of the heat release and therefore a better engine performance.

An engine condition 2000 rpm/100 Nm has been tested varying diesel oil quantity from FD to DF up to 90% of diesel replacement with NG.

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DIESEL INJECTOR COMMAND SIGNAL

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DF condition at NG max (90%) the two command signals for pilot and main are quite similar also similar quantities of diesel injected are expected.

Since the total diesel oil in this condition is 2 mg/cycle (like experimentally measured) it has been assumed that the pilot amount is exactly the half one, i.e. 1 mg/cycle.

So that from this experiment find out the amount of diesel injected for ignition.

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EXPERIMENTAL RATE OF HEAT RELEASES

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varying only the main injection duration and therefore the corresponding injected mass of diesel oil Fuel injected at pilot period remains constant. Air mass trapped was almost constant.

During the tests only the diesel oil amount during the main injection was reduced and replaced by a corresponding quantity of natural gas.

Engine performance level (load = 100 Nm and speed = 2000 rpm) did not change significantly.

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EXPERIMENTAL MASS FRACTIONS OF POLLUTING SPECIES

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CO2 EMISSION

co 2 p.p.m

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EXPERIMENTAL PRESSURE CYCLE

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NUMERICAL STUDY The computational activities and simulation of the in-

cylinder phenomena have been carried out by using the solver KIVA-3V.

This study aims examine in cylinder dual fuel combustion process and exploring main characteristics of this new technology in terms of performance & pollutant formation.

The feeding process is obtained by mixed NG & air introduced into the cylinder & pilot diesel ignite the mixture.

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ENGINE CHARACTERISTICS

Engine 3.0 Multijet

Type 4 stroke C.I.

Common Rail

Number of cylinders 6

Valves /cyl. 4

Bore (mm) 84

Stroke (mm) 90

Cylinder vol. displ. (cm3) 499

Compression ratio 17.6

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INJECTED DIESEL OIL MASS PROFILES

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COMPUTATIONAL DOMAIN AND STRUCTURED MESH

includes inlet & exhausted valve and ducts.

Mesh was obtained by ICEM meshing tool.

Multi block Cartesian grid with the mesh of 104000cells.

More refined grids are possible related with the complication of problem that we are choosing.

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Preliminary investigations have been carried out to determine the correct setting of the atomization models for characterizing the liquid spray pattern inside the cylinder.

The atomization model are experienced in common rail turbocharged diesel engine.

The engine simulation includes the combustion process in order to achieve an overall validation with experimental engine test data.

Self ignition combustion models described for smooth combustion operation.

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THERMO-CHEMICAL PROPERTIES OF CH4-DIESEL OIL BLENDS

NUMERICAL TEST CASES CONDITIONS AT 2000 RPM WITH

DIFFERENT CH4 QUANTITIES

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NUMERICAL RESULTSCH4 % IMEP

(BAR)T (K) at EVO

CO2 % at EVO

CO2 INDEX(Kg/kWh)

0 6.77 1093 10.14 .750

28 6.49 1022 9.95 .765

50 6.77 1036 9.27 .686

72 6.61 1275 8.28 .625

90 6.03 1243 7.095 .658

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IN-CYLINDER PRESSURE CYCLES IN FD AND DF MODE

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DIESEL VAPOR MASS CONSUMPTION RATE

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CH4 CONSUMPTION RATE

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AVERAGE TEMPERATURES AT DIFFERENT CH4 CONTENT

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COMPUTED NO FRACTIONS AT DIFFERENT CH4 CONTENTS

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TEMPERATURE DISTRIBUTIONS [K] FOR DIFFERENT CH4 RATIOS AT TDC CH4 50% CH4 90%

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NO DISTRIBUTIONS [PPM] FOR DIFFERENT CH4 RATIOS AT TDC CH4 50% CH4 90%

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COMPUTED CO AND CO2 FRACTIONS AT DIFFERENT NG CONTENTS

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A NUMERICAL - EXPERIMENTAL COMPARISON

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Comparison of experimental and numerical NO and CO2 fractions

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CONCLUSIONS The experimental data and numerical results from CFD cases

allowed the authors to perform a comprehensive analysis of diesel engine response.

DF mode with variable rates of NG in the F/A mixture entering the cylinders are used for experiment.

NG rates up to 50% the engine behavior is almost similar to that in full diesel operation in terms of lean combustion development and as regards the nitric oxide.

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Increasing the NG rate at 70 – 90 % levels induces an engine behavior that is comparable with the one of spark ignition engines close to knocking conditions.

Different behavior of the engine when increasing the natural gas ratio.

Co and co2 values are decreasing when increasing NG rates but Nox emission increases so that NG 50% is compromise both the values.

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REFERENCES Swami Nathan S., Mallikarjuna J.M., Ramesh A.. An experimental study of the biogas–diesel

HCCI mode of engine operation.

Cameretti M.C., Tuccillo R.. Numerical Simulation of an EGR Operated C.R. Diesel Engine,

ASME paper ICEF 2009 - 14082.

Rahimi A., Fatehifar E., Saray R. Khoshbakhti.. Development of an optimized chemical kinetic

mechanism

compression ignition combustion of a fuel blend of n-heptane and natural gas using a genetic

algorithm.

Carlucci A. P., de Risi A., Laforgia D., et al.. Experimental investigation and combustion

analysis of a direct injection dual-fuel

Cordiner S., Gambino M., Iannaccone S., et al.. 2008. Numerical and Experimental Analysis of

Combustion and Exhaust Emissions

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