Exhaust Gas Recirculation Full Seminar Report 87745

8/11/2019 Exhaust Gas Recirculation Full Seminar Report 87745

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1. INTRODUCTION

All internal combustion engines generate power by creating explosions using fuel and air. These explosions occur inside the

engine's cylinders and push the pistons down, which turns the crankshaft. Some of the power thus produced is used to prepare the

cylinders for the next explosion by forcing the exhaust gases out of the cylinder, drawing in air (or fuel-air mixture in non-diesel

engines, and compressing the air or fuel-air mixture before the fuel is ignited.

Fig 1. Working of four stroke engine.

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There are se#eral differences between diesel engines and non-diesel engines. $on-diesel engines combine a fuel mist with air

before the mixture is taken into the cylinder, while diesel engines in%ect fuel into the cylinder after the air is taken in and compressed.

$on-diesel engines use a spark plug to ignite the fuel-air mixture, while diesel engines use the heat created by compressing the air in the

cylinder to ignite the fuel, which is in%ected into the hot air after compression. &n order to create the high temperatures needed to ignitediesel fuel, diesel engines ha#e much higher compression ratios than

gasoline engines. ecause diesel fuel is made of larger molecules than gasoline, burning diesel fuel produces more energy than burning

the same #olume of gasoline. The higher compression ratio in a diesel engine and the higher energy content of diesel fuel allow diesel

engines to be more efficient than gasoline engines.

1.1. Formation of Nitrogen Oxides (NOx)

The same factors that cause diesel engines to run more efficiently than gasoline engines also cause them to run at a higher

temperature. This leads to a pollution problem, the creation of nitrogen oxides ($x. )ou see, fuel in any engine is burned with extra

air, which helps eliminate unburned fuel from the exhaust. This air is approximately *+ nitrogen and ! oxygen.

hen air is compressed inside the cylinder of the diesel engine, the temperature of the air is increased enough to ignite diesel fuel

after it is ignited in the cylinder. hen the diesel fuel ignites, the temperature of the air increases to more than /00 1 and the air

expands pushing the piston down and rotating the crankshaft.

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Fig 2. NOx formation one.

2enerally the higher the temperature, the more efficient is the engine

. 2ood 3erformance

!. 2ood 4conomy

Some of the oxygen is used to burn the fuel, but the extra is supposed to %ust pass through the engine unreacted. The nitrogen, since it

does not participate in the

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combustion reaction, also passes unchanged through the engine. hen the peak temperatures are high enough for long periods of time,

the nitrogen and oxygen in the air combines to form new compounds, primarily $ and $!. These are normally collecti#ely referred to

as 5$x6.

1.2. !ro"#ems of NOx

$itrogen oxides are one of the main pollutants emitted by #ehicle engines. nce they enter into the atmosphere, they are spread

o#er a large area by the wind. hen it rains, water then combines with the nitrogen oxides to form acid rain. This has been known to

damage buildings and ha#e an ad#erse effect on ecological systems.

Too much $x in the atmosphere also contributes to the production of S72. hen the sunrays hit these pollutants S72 is

formed. $x also causes breathing illness to the human lungs.

1.$. %!& %mission 'tandards

Since +**, $x emissions from diesel engines ha#e been regulated by the 43A

(4n#ironmental 3rotection Agency. &n ctober !00!, new $x standards re8uired the

diesel engine industry to introduce additional technology to meet the new standards

The 43A has regulated hea#y duty diesel engines since the +*0s. The following chart shows the trend to e#er-lower emissions.

9nderstanding the details of the chart is not of interest to most truckers. 4#en though the emissions standards become increasingly more

difficult to meet, the diesel engine industry has always been able to continue to impro#e engine durability, reliability, performance, and

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fuel economy. A 8uick look at the bottom right hand side of the chart also shows that emissions from diesel engines built in !00* and

beyond will approach :ero.

Fig $. %!& ea* Dut* %ngine %mission 'tandards

1.+. o, -an NOx "e redu-ed

Since higher cylinder temperatures cause $x, $x can be reduced by lowering cylinder temperatures. ;harge air coolers are

already commonly used for this reason.


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>owering the compression ratio and retarding ignition timing.

owering the compression ratio and


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!. 4@?A9ST 2AS


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42< ;ooler

42< Transfer 3ipe

Typical 1our Stroke Ciesel 4ngine with asic 3arts of 42


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hen 42< is re8uired engine electronic controls open the 42< #al#e. The exhaust gas then flows through the pipe to the cooler. The

exhaust gases are cooled by water from the truck cooling system. The cooled exhaust gas then flow through the 42< transfer pipe to the

intake manifold.

Figure 4

2.$. %R O0erating Conditions

There are three operating conditions. The 42< flow should match the conditions

. ?igh 42< flow is necessary during cruising and midrange acceleration

!. >ow 42< flow is needed during low speed and light load.

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. $o 42< flow should occur during conditions when 42< flow could ad#ersely affect the engine operating efficiency or #ehicle

dri#ability. ie, during engine warm up, idle, wide open throttle, etc.

2.+. %R Im0a-t on %C' The 4;7 (4lectronic ;ontrol 7achine considers the 42< system as an integral part of the entire 4;S. Therefore the 4;7 is

capable of neutrali:ing the negati#e aspects of 42< by programming additional spark ad#ance and decreased fuel in%ection duration

during periods of high 42< flow. y integrating the fuel and spark control with the 42< metering system, engine performance and the

fuel economy can actually be enhanced when the 42< system is functioning as designed.

2.3. %R T/eor* of O0eration

The purpose of the 42< system is to precisely regulate the flow under different operating conditions. The precise amount of

exhaust gas must be metered into the intake manifold and it #aries significantly as the engine load changes. y integrating the fuel and

spark control with the 42< metering system, engine performance and the fuel economy can be enhanced. 1or this an 4;7 (4lectronic

;ontrol 7achine is used to regulate the 42< flow. hen 42< is re8uired 4;7 opens the 42< #al#e .The 4;7 is capable of

neutrali:ing the negati#e aspects of 42< by programming additional spark ad#ance and decreased fuel in%ection duration during periods

42< flowThe exhaust gas then flows through the pipe to the cooler. The exhaust gases are cooled by water from the #ehicleDs cooling

system. The cooled exhaust gas then flow through the 42< transfer pipe to the intake manifold.

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Fig 5. Re#ations/i0 "et,een %R Ratio and 6oad

+. %R 6I7IT'

This is based on an experiment conducted. The research ob%ecti#e is to de#elop fundamental information about the relationship

between 42< parameters and diesel combustion instability and particulate formulation so that options can be explored for maximi:ing

the practical 42< limit, thereby further reducing nitrogen oxide emissions while minimi:ing particulate formation. A wide range of

instrumentation was used to

ac8uire time-a#eraged emissions and particulate data as well as time-resol#ed combustion, emissions, and particulate data. The

results of this in#estigation gi#e insight into the effect of 42< le#el on the de#elopment of gaseous emissions as well as mechanisms

responsible for increased particle density and si:e in the exhaust. A sharp increase in hydrocarbon emissions and particle si:e and density

was obser#ed at higher 42< conditions while only slight changes were obser#ed in con#entional combustion parameters such as heat

release and work. Analysis of the time-resol#ed data is ongoing.

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The ob%ecti#e of this work is to characteri:e the effect of 42< on the de#elopment of combustion instability and particulate

formation so that options can be explored for maximi:ing the practical 42< limit. e are specifically interested in the dynamic details

of the combustion transition with 42< and how the transition might be altered by appropriate high-speed ad%ustments to the engine. &n

the long run, we con%ecture that it may be possible to alter the effecti#e 42< limit (and thus $x

performance by using ad#anced enginecontrol strategies.

4xperiments were performed on a .+ liter, four-cylinder Bolkswagen turbo-charged direct in%ection engine under steady state, low

load conditions. 4ngine speed was maintained constant at !00 rpm using an absorbing dynamometer and fuel flow was set to obtain

0 full load at the 0 42< condition. A system was de#ised to #ary 42< by

manually deflecting the 42< di#erter #al#e. The precise 42< le#el was monitored by comparing $x concentrations in the exhaust and

intake. $x concentrations were used because of the high accuracy of the analy:ers at low concentrations found in the intake o#er a wide

range of 42< le#els.

+.1. Com"ustion C/ara-teriation ,it/ C and NOx %missions

Steady state measurements were made of ;, ;!, ?;, $x, and ! concentrations in the raw engine-out exhaust using


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Fig 8. Trade9off "et,een C and NOx -on-entration as a fun-tion of %R 6ee#

Time-a#eraged ?; and $x concentrations in the raw engine-out exhaust are shown in the 1igure #ersus 42< le#el. This figure

shows $x

concentration decreasing and ?; increasing with increasing 42< as would be expected. $ote the sudden increase in ?; andle#eling-off in $x at approximately "/ 42


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+.2. Com"ustion C/ara-teriation ,it/ !7

ur measurements ha#e identified significant changes in 37 emissions with 42< le#el as was expected. Similar to the gaseous

emissions (e.g., ?; and $x, there was a sharp increase in 37 at a critical 42< le#el. This critical le#el corresponding to a sharp

increase in 37 was obser#ed in mass concentration, particle si:e, and particle density.

a) 7ass Con-entration

A Tapered 4lement scillating 7icrobalance (T47 was used to measure particulate mass concentration and total mass

accumulation as a function of time. A sample of diluted exhaust is pulled through a ! mm filter to the end of a tapered 8uart: element.

The fre8uency of the element changes with mass accumulation. The instrument has approximately sec resolution on mass

concentration.

3article mass concentration and total mass accumulation were measured on dilute exhaust using the T47. 7ass accumulation

rates were calculated based on o#er 00 mass data points and are shown in the figure as a function of 42< le#el. 7ass accumulation

rates begin to increase significantly at 0 42< and continue to increase rapidly until the maximum 42< le#el. The intersection of the

particulate mass and $x cur#es represents a region where the engine out particulate mass and $ x concentration are minimi:ed for this

engine condition.

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Fig :. Re#ation of !7 &--umu#ation Rate and NOx emission ,it/ %R.

") !arti-#e 'ie

A Scanning 7obility 3article Si:er (S73S was used to measure the steady state si:e distribution of the particulates in the exhaust

stream. The particles are neutrali:ed and then sorted based on their electrical mobility diameter. The range of the S73S was set at nm

E /0/ nm.

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3article si:ing was performed on dilute exhaust using the S73S. $umber concentration #s. particle diameter is shown in the figure

for se#eral 42< le#els. Two aspects of the data stand out. The first is the increasing number concentration with le#el of 42


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measured si:e distribution appears larger than the /00 nm upper bound of the S73S for the highest 42< rates. This is significant

because these particles contain much of the exhaust particulate mass.

The fre8uency plot in the figure illustrates the disappearance of small particles and the growth of much larger particles. The

di#ergence between the cur#es for particles F 00 nm and particles G0-00 nm increases significantly at 0 42< and continues to

increase. The figure does appear to show that the smallest particles are contributing to the growth of the largest ones. The increase in

larger particles is less steep than the increase in particle mass in the figure.

1ig . 1re8uency of occurrence of particle si:e classes as a function of 42


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+.$. NOx redu-tion effe-t of %R

Fig. 12 shows the typical $x reduction effect of 42< at the mid-speed range of the test engine.9nder all load conditions, the

amount of $x decreases as the 42< rate increases. The graph also shows that the $x reduction cur#es with the 0 42< point as

the origin slope downward at different angles according to the loadH the higher the load, the steeper the angle. &n other words, the $x

reduction effect at the same 42< rate

increases as the engine load becomes higher.

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Fig.12. Relationship between EGR rate and NOx

&t is generally known that there are two reasons to reduce $x by 42


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1ig !


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42< (in contrast to external 42


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;ontrol systems for modern engines ha#e been de#eloped o#er two decades and in#ol#e integrated strategies to ad%ust air=fuel

ratio, ignition timing, and air flow rates to maintain emissions control at #arying loads, speeds, and fuel conditions. These systems are at

the heart of successful engine operation today and are #ital to satisfactory long term operation. Adding 42< into the combustion process

introduces further complexity that must be carefully integrated into the entire engine control system approach for successful operation

o#er a wide range of conditions. 1or instance, if fuel 8uality changes o#er time, the air=fuel ratio, ignition timing, air system rates, and

the 42< rate must be ad%usted accordingly to keep the combustion system stable and emissions in compliance. n the other hand, if the

engineDs load changes rapidly from part load to full load and back to part load, the 42< system dynamics must be included in the o#erall

control strategy response to make sure the engine operates smoothly during this transition.

4.$. 7ateria#s and Dura"i#it*

42< systems may decrease long-term life of the components affected, including the 42< coolers and control #al#es, the pistons

and cylinder heads, exhaust manifolds and sensors, as well as the post engine catalyst. perating a few hundred hours per year may not

lead to any significant materials degradation in the o#erall lifespan of an engine. ?owe#er, continuous duty applications at J/00 hours

per year may cause near term emissions noncompliance and longer term materials breakdown, shorter component life, and e#en

unexpected, catastrophic engine failures. To minimi:e or eliminate the potentially negati#e impacts of 42< on engine components,

compatible components and designs must be used that often re8uire thousands of hours of lab and field test operation for #alidation.

Although both expensi#e and time consuming, such efforts are a necessary part of pro#ing any new combustion design including 42


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4.+. 6i;uid Dro0out

Curing exhaust gas recirculation, the gasses must be cooled with an external cooler before being reintroduced into the cool inlet

manifold of an engine. The cooling process for the 42< may result in li8uids being formed in the return lines, depending on

temperatures and local humidity, much as li8uids are formed in the tailpipe of an automobile at certain conditions. This li8uid dropout

could be a continuous stream that needs to be carefully understood and managed with the needs of the local en#ironment in mind. hile

there may be ways to reintroduce this li8uid into the combustion process, doing so may create further problems with combustion and

lead to other emissions complications and instability. As such, managing li8uid dropout needs careful study and de#elopment in an

integrated de#elopment program.

5. CONC6U'ION

Thus, as seen that using 4xhaust 2as


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Exhaust Gas Recirculation Full Seminar Report 87745

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