comprehensive study of biodiesel fuel for hsdi engine

8/11/2019 Comprehensive Study of Biodiesel Fuel for HSDI Engine

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IC engines using diesel as fuel are used mostly in heavy vehicles

These engines are producing lots polluting gases like CO2,CO,NOX etc. in combustion process which are responsible for global

warming

The fossil fuels are going to exhaust in near future

As result, the research effort in the field of alternative fuel isincreased to face the above problems

Several studies have shown that vegetable oils( bio-diesel) can

be used as alternative fuels in conventional diesel engine

because they have low CO2 emission and the future will be

independent of fossil fuel


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Vegetable oils cant be used in diesel engines directly

because its low temperature fluid properties. By

converting this oil to ester by transesterificationprocess which reduces its viscosity and density its

property will become nearly similar to that of diesel.

The main objective of this research is study of

combustion characteristic of biodiesel in DI enginewhich can be attained by comparing biodiesel with

diesel in wide range of operating conditions


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Bio diesel diesel

Lower heating value [MJ/kg] 36.79 42.84

Stoich A/F ratio 12.6 14.56

Density @ 15 C [kg/m3] 882.5 843.0

Viscosity @ 40 C [mm2/s] 4.304 2.847

Cetane number 52.9 51.0

Acid value [mgKOH/g] 0.29 -

Total glycerol [%] 0.1 -

Free glycerol [%]


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this methodology based on experimental test performed in single

cylinder diesel engines since this type of facility generate more

accurate data compared to multi cylinder engines.

Test engine is peugeot 1.6 lit single cylinder diesel engine which is

equipped with second generation common rail injection system

Bore(mm) 88

Stroke(mm) 76

Displacement volume(mm) 0.399

Connecting rod length(mm) 123.8

Eccentricity (mm) 1

Compression ratio 17:1

Maximum speed(rpm) 4500

Injection system Common rail 160mpa

with solenoid control

Characteristics of single cylinder engine


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Scheme of single cylinder research engine and

complete test cell


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In cylinder pressure

By kistler 6043A

Pressure measured per 25 cycles

quantity of pollutants

Un burned hydrocarbons(UHC). Nox,CO,CO2

By horiba7100

Smoke emission

measurement of soot emissionby AVL smoke meter

unitfilter smoke number


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EGR system is used in this system

While evaluating dilution level EGR rate can be used as a parameter . But

it is different value depending on the chemical composition of the fuel.

The most appropriate parameter to quantify the dilution between the

fresh air and exhaust is the YO2intake

Dilution level

Load level

The oxygen mass consumed during the combustion has been

considered as the most suitable parameter to quantify the load level

The consumed oxygen should be quantified in the following way:

YO2intakeYO2exhaust

YO2 intake = YO2atm(1-EGR)+YO2exhaust.EGR


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ENGINE OPERATING CONDITIONS

Operating

conditions

Injection

pressure(mpa)

Injection

strategy

Injection

timingp /m(BTDC)

A 61 Pilot injection+Main injection

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B 61 Pilot injection +Main injection

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C 61 Main injection -/6

D 100 Pilot injection +Main injection 24/14

All the operating conditions are centered in condition A . Only one

parameter is was modified while moving to any other operating

conditions


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Sample maps for comparison


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Result and discussion

The analysis of the experimental results obtained withconventional diesel and neat biodiesel have been divided

into two progressive and complementary steps

1. Description of combustion performance

2. Insight physical biodiesel combustion phenomena

1.Description of combustion performance

Main parameters to be checked

1. End of combustion angle

2. Indicated efficiency3. Exhaust gas temperature

4. Combustion induced noise


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1.End of combustion angle

The end of combustion angle

defined as the crank angle at which

total heat has been released

The map confirm an early EOC for

biodiesel than that for diesel fuel.

Start of ignition is same for all test

so shorter combustion process

Map comparing EOC observed

using neat biodiesel and diesel fuel


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Ratio maps of CO, UHC,density and adiabatic

temperature


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3. Exhaust gas temperature

Higher indicated efficiency indicates

better conversion of thermal energyinto mechanical energy.

So the thermal energy remaining in

the exhaust gases should be lower

Its results in low exhaust

temperatureIn the low pressure combustion

region the exhaust temperature is

critical even for diesel fuel due to its

negative effects of turbocharger

performance. So the lower exhaust

temperature observed for biodiesel

could be a major draw back for its

applicability in future diesel engines


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4. Combustion induced noise

In case of biodiesel fuel the

combustion noise is slighted

reduced compared to the diesel

fuel.

It takes place during the pre-

mixed combustion stage

It is directly linked with thepressure gradient and it is

estimated by instantaneous

pressure signal


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Physical biodiesel combustion phenomena

Due to complexity of combustion process this analysis is divided into

three phases

1. Ignition delay

2. Premixed combustion

3. Mixing controlled combustion

Ignition delay and premixed combustion isanalyzed in the operating condition C(only main

injection)

mixing controlled combustion is analyzed in the

operating condition A


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1 . Ignition delay and premixed combustion stage

Ignition delay corresponds to beginning of the fuel injection

until the cylinder rise in pressure i.e the start of combustion

ID= SOC - ( SOI + Hydraulic time delay)

This reduction of ignition delay is mainly caused due to

different in physical composition and chemical properties of the

fluid

Higher cetane number also responsible for the shorter ignitiondelay


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Comparison of ignition delay and premised combustion parameters

between biodiesel and diesel in operating condition C


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Neat biodiesel reduces the premixed combustion

period and also the mass of the fuel burnt in premixed

condition

The effect of dilution is evident in this premixed

combustion stage

Because the premixed combustion duration increases

as YO2intake is reducedAs biodiesel shortens the ignition delay it is more

difficult to attain a highly premixed combustion for

reducing NOx emission

Premixed combustion directly related to the ignitiondelay


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From the first hypothesis

Where

FL=flame length

Considering the profile velocity along the axial direction of

gaseous jet

Mixing time=

Integrating this equation we will get


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From this equation two opposite effects has been detected

Stoichiometric air/fuel ratio is higher than the density

ratio and the ST ratio is squared but the density ratio is

square rooted

So mixing time of biodiesel is shorter than that of diesel


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The apparent time of combustion (ACT) for biodiesel is shorter than

that of diesel engine

The lower heating value of diesel requires longer injection duration to

introduce same quantity of energyRelation between the injection time of the two fuels


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The experimental value obtained is 0.87It signifies that it have shorter combustion period

It justifies the early end of combustion

Two situation has been observed i.e for tmixing and

for tinjection

Shorter combustion

periodLonger combustion

period


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conclusionUniversal methodology used based on practical and robust

parameter which includes broad range of operating condition

Biodiesel have faster combustion process and slight increase

in indicated efficiency

Lower emission of CO2 , CO and UHC. But NOx emission

increased for bio diesel

Mixing time shorter and faster combustion , these results

are valid for conventional and low pressure combustionconditions

It is a promising fuel for HSDI diesel engines operating with

current and future contents


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reference

Comprehensive study of biodiesel fuel for HSDI engines

in conventional andlow temperature combustion

conditions

Authors

Bernardo Tormos*, Ricardo Novella, Antonio Garca,

Kevin Gargar

CMT-Motores Termicos, Universidad Politecnica de Valencia, Valencia, ES, Campus de Vera, s/n, Edificio 6D.

Camino de Vera s/n, 46022 Valencia, Espana

Collected from journal ELSEVIER


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