REDUCTION OF NOX EMISSION IN BIODIESEL

ENGINES BY EXHAUST GAS

AFTERTREATMENT METHOD

KUMARAGURU COLLEGE OF TECHNOLOGY

BE - MECHANICAL III YEAR

SHANMUGAM B VIJAY KUMAR D

99942 64689 99940 19619

shanmugamkct@gmail.com

vijaytriumph@gmail.com

CONTENTS

Topics Page no.

Abstract 3

Introduction about biodiesel 4

Key advantages of biodiesel 4

Percentage change in emissions for

B20, B100, and diesel 5

Disadvantages of biodiesel 6

NO and NOx formation theories 6

NOx reduction methods 7

Exhaust gas aftertreatment system 8

Parts of EGAS 8

Description 8

Working of EGAS 9

Block diagram of EGAS 10

Disadvantages of EGAS 11

Conclusion 11

Reference 11

2

REDUCTION OF NOX EMISSION IN BIODIESEL

ENGINES BY EXHAUST GAS

AFTERTREATMENT METHOD

ABSTRACT:

Depletion of fossil fuels and environment degradation are the two major

reasons for the search of alternative source of fuels. Biodiesel is best suit for present

automobile engine with or without minor changes in the engine. Biodiesel-fuelled

engines produce less carbon monoxide, unburned hydrocarbon, and particulate

emissions compared to conventional diesel fuel but higher NOx emissions - the

greatest threat to the ozone layer. This behavior is attributed to the higher content of

oxygen in the biodiesel. The theories of formation of NOx have also been discussed.

Recent developments in engine and exhaust aftertreatment technologies have emerged

as effective methods to reduce NOx emissions with a significant emphasis on the use

of Exhaust Gas Aftertreatment System (EGAS). EGR (Exhaust Gas Recirculation)

works by recirculating a portion of an engine's exhaust gas back to the engine

cylinders. Intermixing the incoming air with recirculated exhaust gas dilutes the mix

with inert gas, lowering the adiabatic flame temperature and (in diesel engines)

reducing the amount of excess oxygen. The exhaust gas also increases the specific

heat capacity of the mix lowering the peak combustion temperature. Because NOx

formation progresses much faster at high temperatures, EGR serves to limit the

generation of NOx. NOx is primarily formed when a mix of nitrogen and oxygen is

subjected to high temperatures. In order to evaluate if this technique is also valid for

Biodiesel blends, a review is made concerning the effect of EGR on emissions of

3

diesel engines running with different Biodiesel blends and for different EGR rates.

Data about conventional diesel are also shown for comparison purposes. Similar

results were found in both cases and conclusion can be drawn that NOx emissions

decrease with the increasing of EGR rate. The degree of reduction in NOx at higher

loads is also higher. The reasons for reduction in NOx emissions using EGR in diesel

engines are reduced oxygen concentration and decreased flame temperatures.

KEY WORDS: Biodiesel, formation, emission of NOx, Exhaust Gas Recirculation.

INTRODUCTION

BIODIESEL:

Biodiesel are the fuels made from biological ingredients instead of fossil fuels.

These starting ingredients can range from corn to soybeans to animal fat, depending

on the type of fuel being made and the production method.

According to the National Biodiesel Board (NBB), the technical definition of

Biodiesel is as follows: A fuel comprised of mono-alkyl esters of long chain fatty

acids derived from vegetable oils or animal fats, designated B100, and meeting the

requirements of ASTM D 6751.

BIODIESEL HAS SEVERAL KEY ADVANTAGES:

Biodiesel has fewer emission and hence environment friendly

Biodegradable – It’s a renewable source of energy. It can help reduce

dependency on foreign oil. It helps to lubricate the engine itself, decreasing

engine wear and increases the Engine life. It can be used in almost any diesel

4

engine with little or no modification. It is non toxic and has higher flash point and

hence safer than conventional Diesel.

PERCENTAGE CHANGE IN EMISSIONS FOR B20, B100, AND DIESEL

DISADVANTAGES OF BIODIESEL

Of course, nothing is without penalty, and Biodiesel does have its drawbacks.

Some have to do with the fuel itself, and many have to do with the bigger picture.

Average Biodiesel Emission Compared to Conventional Diesel

Emission Component

B100 B20

Total Unburned

Hydrocarbons

-67% -20%

Carbon Monoxide

-48% -12%

Particulate Matter

-47% -12%

NOx +10% +2%Su;phates -100% -20%

PAH -80% -13%Source: National Biodiesel Board

5

Biodiesel behaves as a solvent, which causes clogging in engines. Because of its

ability to loosen deposits built up in the engine, Biodiesel can cause the fuel filter to

become jammed with the newly freed deposits. Also, in some engines, there can be

slight decrease in fuel economy and power. The most important is cost. More

important issue is that of amount and availability. Increase in NOx in Biodiesel

emissions, which contribute to smog formation.

NO AND NOx FORMATION THEORIES

The chemical kinetics of NO and NO2 are presented below. The oxides of

nitrogen formation pathways such as thermal NO and nitrogen dioxide formation are

discussed.

Thermal, or Zeldovich, NO

It was Zeldovich who introduced the NO formation reactions for the first time in

1946. These reactions describe the NO formation in the post flame region and are also

called the thermal NO mechanism given in Reactions 1 and 2.

O + N2 NO + N (1)

N + O2 NO + O (2)

In 1956, Fenimore and Jones proposed a third equation in addition to those of

Zeldovich suggesting that Reaction 3 might be more important than Reaction 2 for

fuel rich reactions. The three equations are now known as the Extended Zeldovich

mechanism

N + OH NO + H (3)

Temperature is very important for the Zeldovich mechanism because of the high

activation energy requirement of the first reaction and the need for dissociation of O2.

The extended Zeldovich mechanism describes the formation of NO in the post-flame

gases of fuel-lean and slightly fuel-rich mixtures.

6

2.3.6. Nitrogen Dioxide (NO2) Formation

In flue gas, the concentration of NO2 is generally not more than 5% of the total NOx

concentration.

2 NO +O2 2 NO2 (4)

NO + HO2 NO2 + OH (5)

It has been claimed that Reaction 4 is too slow to be significant at typical NO

concentrations. Reaction 5 is the faster path for NO2 formation. Reaction 5 is

important when HO2 concentration is high between 600 -1000K. At higher

temperatures, HO2 dissociates to atomic H, O2, and OH and leads to destruction of

NO2 by the following reactions. Thermal NO is the dominant mechanism in diesel

combustion

O + NO2 NO + O2 (6)

H + NO2 NO2 + OH (7)

OH + NO2 NO + HO2 (8)

. The mechanism shows the effect of temperature in the formation NOx.

Higher the temperature more is the NOx formation.

NOX FORMATION CAN BE REDUCED BY:

Enriching the air fuel (A/F) mixture to reduce combustion temperatures.

However, this increases HC and carbon monoxide (CO) emissions.

Lowering the compression ratio and retarding ignition timing; but this leads to

reduced performance and fuel economy.

Recirculation of some exhausts.

7

EXHAUST GAS RECIRCULATION (EGR):

These systems are introduced to reduce an exhaust emission that was not being

cleaned by the other smog controls. Oxides of nitrogen (NOx) are formed when

temperatures in the combustion chamber get too hot. At 2500 degrees Fahrenheit or

hotter, the nitrogen and oxygen in the combustion chamber can chemically combine

to form nitrous oxides, which, when combined with hydrocarbons (HCs) and the

presence of sunlight, produces an ugly haze in our skies known commonly as smog.

PARTS OF EGR:

EGR Valve

EGR Transfer Pipe(Hot)

EGR Transfer Pipe (Cool)

EGR Cooler

DESCRIPTION

An exhaust control valve is fitted to the exhaust line of the engine. This

creates a back pressure in the line, so a portion of the exhaust enters into the EGR

transfer pipe (Hot). Then it passes through the EGR cooler to reduce the exhaust gas

temperature to a required level. This exhaust then enters the EGR transfer pipe (Cool)

and reaches the EGR control valve. The outlet of this valve is connected to the inlet

manifold of engine. The EGR valve decides the quantity of exhaust mixing with the

fresh air.

8

WORKING OF EGR SYSTEMS:

The EGR valve recirculates exhaust into the intake stream. Exhaust gases have

already combusted, so they do not burn again when they are recirculated. These gases

displace some of the normal intake charge. This chemically slows and cools the

combustion process by several hundred degrees, thus reducing NOx formation. Hot

exhaust exits the engine through the exhaust manifold. The exhaust then passes

through the EGR valve. While most of the exhaust passes out through the exhaust

system, the EGR valve diverts a measured amount of exhaust into the EGR system.

This dilutes the oxygen used by the engine, which lowers the combustion temperature

and reduces the amount of NOx produced.

9

The combined exhaust and inlet air enters the engine's cylinders, goes through

the combustion cycle and exits the engine through the exhaust manifold.

BLOCK DIAGRAM OF EGR SYSTEM

High flow is necessary during cruising and mid-range acceleration, when combustion

temperatures are typically very high.

Low flow is needed during low speed and light load conditions.

No flow should occur during conditions when EGR operation could adversely affect

engine operating efficiency or vehicle driveability (engine warm up, idle, etc.)

By using EGR output power of the engine will reduce due to reduction in oxygen

supply. This may save fuel but however to compensate the reduction in power a

simple turbo charger can be used.

DISADVANTAGES OF EGR

10

Due to mixture of exhaust gas with the fresh air in the inlet, there will be

lesser amount of oxygen which directly results in reduction of output power.

But this loss in output power can be overcome by using a simple turbocharger.

CONCLUSION

By using exhaust gas recirculation system which is the exhaust gas

aftertreatment method, the emissions of oxides of nitrogen can be reduced

considerably. This method results in decreased NOx emissions and there will also be

reduction in the output power of the automobile due to lesser supply of fresh air. By

this method one of the harmful emission by the biodiesel is reduced and making

biodiesel more eco-friendly.

Reference:1) Production of Biodiesels from Multiple Feedstock and Properties of Biodiesels and Biodiesel/Diesel Blends, Final Report Report 1 in a series of 6, March 2003 NREL/SR-510-31460 by J.A. Kinast Gas Technology Institute Des Plaines, Illinois

2) NOx Solutions for Biodiesel Final Report, Report 6 in a series of 6, NREL/SR-510-31465 , February 2003 by R.L. McCormick, J.R. Alvarez, and M.S. Graboski Colorado Institute for Fuels and Engine Research Colorado School of Mines Golden, Colorado

3). 38296NOx Emissions Reduction in a Biodiesel Engine by Means of EGR TechnologySAE 2007-01-0078 Author(s): Eliseu Magalhães, Monteiro - Tecaprod S.A. 4) Combined Impact of Biodiesel and Exhaust Gas Recirculation on NOx Emissions Citation:  Paper number 066136, 2006 ASAE Annual Meeting. @2006 Authors:   Seth J. Wenzel, Alan C. Hansen, Wenqiao Yuan5) Understanding Exhaust Gas Recirculation Systems by Henry Guzman, www.autoinc.com6) Investigation of oxides of nitrogen emissions from biodiesel-fueled engines by Mustafa Ertunc Tat, Jon H. Van Gerpen, Howard N. Shapiro, Ron M. Nelson, Brent H. Shanks, Steven J. Hoff, Iowa State University Ames, Iowa 20037) Effects of Biodiesel on NOx Emissions, by Bob McCormick National Renewable Energy Laboratory Golden, Colorado ARB Biodiesel Workgroup, June 8, 2005NREL/PR-540

11

12