International Journal of Advances in Thermal Sciences and EngineeringVolume 2 • Number 2 • July-December 2011, pp. 97-106

* Research Scholar, (e-mail : sreckca@yahoo.co.in)** Professor, Department of Mechanical Engineering, Anna University, Chennai 25, India.*** Former Director, Research, Anna University, Chennai-25.

REDUCTION OF NOX IN D.I. DIESELENGINE EMISSION BY UREA INJECTION

K. Chithambaramasari,* N. V. Mahalakshmi** & K. Jayachandran***

ABSTRACT: Injection of aqueous solutions of urea in the exhaust for the reduction of NOx was investigated in a singlecylinder light duty D.I. diesel engine. Several kinds of concentration of urea solution varying from 5% to 50% byweight with different flow rates of urea solution varying from 250ml/hr to 7000ml/hr were tested. Results show thatmore than 28% NOx reduction was achieved with the flow rate of 750 ml/hr for 30% concentration and 82% NOxreduction was achieved with the flow rate of 2250ml/hr for the same concentration.

Keywords: Diesel engine; NOX; Urea Solution.

1. INTRODUCTIONDiesel engines are widely used in many areas like Automobiles, locomotives marine engines powergenerations etc., due to its high power output and thermal efficiency. Even though the diesel enginesgive more benefits, the human discomfort caused by the pollutant emission of these engines have to beconsidered.

The major pollutant emissions of the diesel engines are particulate matters, smoke and the oxides ofNitrogen (NOx). Out of these pollutant emissions, the oxides of Nitrogen are considered as the mostharmful pollutants to the human health. Emissions of nitrogen oxides (NOx) contribute seriously to airpollution, which is a major environmental problem. Emissions of NOx react with moisture in the air toform nitric acid, contributing to soil and water acidification in sensitive areas. The formation of ground-level ozone is caused by photochemical reactions involving primarily NOx.

Ozone is the dominant component of photochemical smog and highly undesirable due to its impacton the human respiratory tract. High ozone levels also cause acute damage to sensitive crops and trees.Hence the diesel engine industries are now under high pressure in finding various methods to minimizethe emission of these oxides of Nitrogen (NOx).

2. FORMATION OF NOX

The pressure of Nitrogen in the atmosphere exists in the form of N2 (di-atomic modulus of Nitrogen)which is highly stable. During the process of combustion a high temperature will occur inside the cylinderat about 800°C to -1000°C. At this high temperature the di-atomic molecule nitrogen N into monoatomicNitrogen 2N which is highly reactive. This monoatomic Nitrogen reacts with the oxygen which is alreadypresent in the cylinder and from oxides of Nitrogen.

Oxides of Nitrogen generally occurs mainly in the form of NO and NO2. These are generally formedat high temperature. Hence higher temperature and availability of free oxygen are the main two reasonsfor the formation of NO and NO2. Many other Nitrogen Oxides like N2O4, N2O, N2O3, N2O5 also formed inlow concentrations but they decomposes spontaneously at ambient conditions of NO2.

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3. CONTROL OF NOThere are many techniques being tried to control Nox emission from diesel engine. The following methodsmay be employed either as a single technique or as a combination.

• Modification of engine operations

• Changes in the engine design

• Modification of fuels

• After treatment of exhaust gases.

3.1. After Treatment of Exhaust Gas by Injecting Urea SolutionIn the after treatment method, Urea solution is sprayed in the exhaust stream which is at a temperature of300°C to 450°C. At this high temperature of exhaust gas, the urea starts to decompose and form ammonia.The ammonia acts as reduction against and converts the oxides of Nitrogen (NO and NO2) into freeNitrogen (N2) and water vapour (H2O).

The following are the chemical reaction taken place.

Figure 1

4. EXPERIMENTAL SETUPThe experiment was conducted in a light duty stationary single cylinder, 4 stroke, water cooled, directinjection Kirloskar Engine as shown in the Figure (2) The engine was connected to an eddy currentdynamometer. The torque can be varied from the control panel. Water cooling system was used forcooling the engine with a separate water cooling pump.

Reduction of Nox in D.I. Diesel Engine Emission by Urea Injection 99

1. Kirloskar Diesel Engine2. Eddy current dynamometer3. Measuring Instrument4. Urea Solution Tank5. Urea Pump6. 3 Way flow Control valve7. Nozzle8. Bosch smoke meter9. AVL 5 gas analyzer10. Control panel11. Computer12. Printer

Table 1Name Plate Details of KIRLOSKAR Diesel Engine

Type Single Cylinder vertical water cooled 4 stroke diesel engine

Bore 87.5mmStroke 110mmCompression Ratio 17.5 : 1Orifice diameter 0.02mDynamometer arm length 0.195mPower 5.2 kW (7HP)Speed 1500 RPMLoading Device Eddy current Dynamometer

Figure 2

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To measure the in cylinder peak pressure and crank angle a piezo electric transducer was mountedon the cylinder head. It is connected to the computer terminals. The engine is fitted with fuel flowmanometer to measure the fuel consumption in a particular period of time.

The species of products of combustion was measured with help of AVL 5 gas analyzer. The smokewas measured by Bosch smoke meter. The water cooled pressure pickup was well prepared and cleanedfrom moisture and mounted carefully on the engine head. The pressure and crank angle signals weresampled as two different channels and signals received from engine were fed into the change amplifier.The received signal is converted and amplified (0 to 5 volt) to analog signal, i.e linear to the change withsubsequent amplification.

A 12 bit ±1 LSB analog to digital card was used to convert the analog signal into digital form. A PCbased AVL high speed digital data acquisition system was used to process the above discussed pressureand crank angle signals.

The A/D card has internal and external triggering facilities. Received signals were processed with asoftware code obtain the combustion parameters like peak pressure, maximum rate of pressure rise,indicated mean effective pressure, heat release etc.

The Exhaust gas after treatment system was mounted on the exhaust pipe line consists of an injectedneedle for injecting urea solution, a storage tank to store urea solution, a pump to maintain the pressureof urea solution and a three way control valve, so that the specified quantity of urea solution could beinjected through the nozzle which is fitted just near to the exhaust pipe and the remaining solution couldbe returned to the storage tank.

5. EXPERIMENTAL METHODOLOGYBefore starting the engine, urea solution should be prepared for different concentration varying from 5%to 50% by weight in the order of 5%. By adjusting the 3 way control valve and selecting the needle theflow rate of urea solution should be fixed and maintained constant for a set of experiment.

Initially the engine was started and allowed the engine with constant speed for some period of time.The engine was loaded gradually in the order of 25%, 50%, 75%, 100% of full load. For every loading thefuel flow rate, emission of HC, CO, CO2, O2, NOX, Smoke Density, Excess Air Factor, Pmax, and Heatrelease were recorded. Repeated the experiment for 3 times. The same reading were recorded for differentconcentration of urea solution with constant flow rate of urea solution.

5. RESULTS AND DISCUSSIONFigure 3 to 14 indicates the variations of various engine parameters with respect to brake power withdiesel as sole fuel without any urea injection in the exhaust.

Figure 15 to 21 indicates variations of various engine parameters with respect to brake power forvarious concentration of urea from 10% to 50% with a flow rate of 0.75 litres/hr.

Figure 18 compares the exhaust gas temperature of engine for various concentration of urea for aflow rate of 0.75 litres/hr. The exhaust gas temperature decreases for the increase of urea concentrationdue to the formation of water in the exhaust as byproduct. The formation of water depends upon theintensity of chemical reaction and which in turn depends upon the concentration of urea.

Figure 19 indicates the variation of smoke density with respect to brake power. The smoke densityincreases with increase of urea concentration.

Figure 20 indicates reduction of NO as the concentration of urea is increased.

Figure 21 Shows the variation of HC for different concentration of urea injection with respect to brakepower. The quantity of HC is lower for various concentration of urea injection compare to base dieselreadings.

Reduction of Nox in D.I. Diesel Engine Emission by Urea Injection 101

The cylinder pressure and heat release rate with respect to crank angle has not shown much differencefor different concentration of urea injection as indicated in the Figure 22 and 23, since urea injection hasnothing to do with the above parameters

Figure 24 to 30 indicates the variations of various engine parameters with respect to brake power for10% urea concentration for various flow rates ranging from 0.25litres/hr to 1 litre/hr.

Figure 3 Figure 4

Figure 5 Figure 6

Figure 7 Figure 8

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Figure 9 Figure 10

Figure 11 Figure 12

Figure 13 Figure 14

Reduction of Nox in D.I. Diesel Engine Emission by Urea Injection 103

Figure 15 Figure 16

Figure 17 Figure 18

Figure 19 Figure 20

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Figure 21 Figure 22

Figure 23 Figure 24

Figure 25 Figure 26

Reduction of Nox in D.I. Diesel Engine Emission by Urea Injection 105

Figure 27 Figure 28

Figure 29 Figure 30

Figure 31

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Figure 31 compares oxides of nitrogen with brake power for 30% concentration and flow rates of0.75litre/hr and 2.25litre/hr with base diesel reading without urea injection. Compare to base dieselwithout urea injection a decrease of 28% of NO was achieved for the flow rate of 750ml/hr and 82% ofNOX reduction was achieved with a flow rate of 2250ml/hr.

6. CONCLUSIONSFrom the investigations it may be Concluded that urea injection in the exhaust gives a reduction of about82% of NOx. Thus this method was found to be an effective method for controlling NOx from DieselEngines.

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