Effect of Nozzle Hole Number on Diesel Engine Using Diesel and Biodiesel Blends

In this work the experiment was carried out to investigate the performance, combustion and emissions by changing the number of nozzle holes of the injector such as 3 hole, 4 hole and 5 hole by maintaining the hole diameter as 0.25mm. The experiments are executed on Kirloskar 4-stroke computerized single cylinder air cooled and electrical dynamometer coupled DI diesel engine with diesel, Rubber seed methyl ester and B20 Blend as fuels at 1500 rpm, with the injection timing of 23.4°BTDC with an injection pressure of 240 bar maintained constant throughout the experiment. It is found that 4 hole nozzle gives higher brake thermal efficiency, lower specific fuel consumption, CO, HC, for Diesel, Biodiesel and B20 Blend compared with other two nozzle holes. However the NOX got increased which is more for all the tested fuels by varying a number of nozzle hole diameter.


Introduction
In a CI engine the diesel is inoculated into an extremely pressurised gas. The pressure and temperature of the gas makes the diesel to self-ignite. Certain time period is essential for self-ignition as the reactions of combustion does not takes place instantly. Hence, the preliminary stage of combustion process is premixing meanwhile certain amount of diesel has time period to combine with air during the ignition delay period. Next to the premixed stage the combustion will takes place with diesel being burnt during controlled combustion stage. As stated earlier the intention of a combustion system in an engine is to burn the fuel and thus turn it into heat. A fuel injector is a device which is used to impinge the fuel into the engine for preparing the correct fuel-air mixture which in turn offers effective combustion to the engine. The capillary and nozzle of diesel fuel injectors are made in such a manner that they can form the diesel packets while spraying the fuel inside the combustion chamber.
The study was made on a DI diesel engine to evaluate its outcome on performance and emission at 200 bar, 220 bar and 240 bar injection pressure. The dissimilar nozzle hole size injectors such as 3 holes 0.28 mm dia and 5 holes 0.20 mm dia were taken. The result shows that the 5 hole nozzle of Ø = 0.2 mm at the fuel injection pressure of 220 bar gives improved performance and emission characteristics [1]. The study was done to evaluate the effect of different nozzle hole sizes on performance, combustion and emissions by using various diameters for a 3hole nozzle. The diameters chosen are 0.28 mm as base and 0.20 mm as modified. It was observed that 0.20 mm modified nozzle progresses the vaporisation, atomisation and air-fuel mixing in a lesser time period [2]. This investigation was done to explore the performance of Jatropha not fit for human consumption vegetable oils and its blend. The trials were executed on 5,7,9 and 11 hole nozzle injector for an injection pressure of 210 bar. It is seen that the 9 hole nozzle provides decent performance and lesser  [3]. This investigation deals with the outcome of diverse constraints which includes hole number, diameter and length of holes, nozzle sac diameter and the needle seat angle of injectors were studied based on injection rate and sac pressure. Outcomes demonstrate that decrease in sac pressure by 46%, therefore doubling the hole number had massive variation in injection rate. Even though, the sac pressure will increase up to 60%, when the hole diameter is decreased by 40% in spite of the quasi-constant injection rate [4].
This study deals with the evaluation of diesel engine's performance using neem oil methyl ester (NOME). The engine runs at a constant speed of 1500 rpm and CR of 17. 5 [6].
The experiment was done to evaluate the performance of CRDI engine using acid oil methyl ester (AOME) biodiesel blended with diesel and ethanol. First the injection timing is varied between 25 o BTDC to 5 o ATDC and next the injection pressure is varied between 600 to 1000 bar. The compression ratio and the engine speed were kept constant at 17.5 and 1500 rpm respectively for both cases. It is evaluated that injection timing of 10 o and the injection pressure of 900 bar gives higher performance and lesser emissions [7].
The diesel engine's performance depends mainly on their injection scheme strategy. Hence the advances were done in the injection system design to achieve better engine performance. The injectors will inject the fuel at very high pressure and thus the material selected must able to withstand the high stresses. Superior accuracy and tolerance were given in the injection system design. Thermocouple is employed to measure the ambient air temperature. An exhaust gas analyzer is employed to calculate the amount CO, CO2, HC, NOx and O2.

Results and Discussions
The experiment was performed to investigate the effect of different nozzle hole number in CI engine. The combustion, performance and emission characteristics of various nozzles are tested under different load conditions using diesel, biodiesel and B20 blend. Some of the engine parameters and emissions are calculated and represented in the form of graphical representation.

Brake thermal efficiency
Brake Thermal Efficiency is known as brake power of a heat engine. It helps to determine how an engine converts heat energy to mechanical energy. Brake thermal efficiency (BTE) measures the effectiveness of chemical energy conversion into beneficial work in an engine. Effect of nozzle hole number on BTE for 3, 4 and 5 hole nozzles for various fuels used are shown in Figure 1 to Figure 3 respectively. Hence it was evaluated that nozzle holes number has substantial impact on spray penetration and droplet size. From the above graphs it was observed that for 4 hole nozzle the BTE amplified slightly as a outcome of improved vaporization and atomization for diesel and RSME. 5 hole nozzle shows increased BTE for B20 blend alone. It is clear that for diesel and biodiesel the 4 hole nozzle is preferred than the other two nozzles for better BTE.      Brake-specific fuel consumption (BSFC) is the fuel efficiency of prime mover in which fuel burns to yield shaft or rotational. Thus BSFC relates the efficiency of an internal combustion engine with its shaft output. It is also the amount of fuel consumed to the power generated. Consequence of nozzle hole number on BSFC for 3,4,5 hole nozzles are shown in Figure 4 to Figure 6 respectively. The BSFC depends principally on fuel aspects such as viscosity, density and its chemical structure. For the 4 hole nozzle, the BSFC was encouragingly falling due to increased mixing rates of fuel and air. From the outcomes it is found that 4 hole nozzle have low BSFC when compared with other nozzles for diesel, bio diesel and B20 Blend fuel.

Heat release rate
HRR is a vital parameter of combustion found by the application of the first law of thermodynamics on the cylinder gas pressure variable. Based on HRR the various combustion stages were classified. The combustion stages are classified into premixed combustion stage, mixed combustion stage, and late combustion stage.   Figure 7. Effect on HRR for Diesel. Figure 8. Effect on HRR for Biodiesel.
Effect on heat release rate for 3, 4 and 5 hole nozzles are shown in Figure 7 to Figure 9 respectively. The peak rise in Heat Release Rate for the 4 hole nozzle is because of the delay during the early stage of combustion.

Cylinder Pressure
The pressure inside the engine cylinder is a vital parameter to be observed during the combustion process to evaluate the performance characteristics of the diesel engine. It is dependent on the amount of fuel taking part in uncontrolled combustion. Variation of cylinder pressure for 3, 4 and 5 hole nozzles are shown in Figure 10 to Figure 12 respectively. From the graphs it is evaluated that the 4 hole nozzle has high in-cylinder pressure compared with the other nozzles. It is due to the complete vaporization of the fuel in 4 hole nozzle and results in appropriate mixing of air and fuel.

Carbon monoxide
Carbon monoxide is mainly due to the partial combustion in which the complete oxidation process does not occurs. CO mainly depends on the air fuel mixture, if the rich mixture is used the level of CO will be higher. In rich mixtures due to shortage in air the CO2 cannot be formed from the carbon and thus CO is formed. The large amount of CO is formed during the starting of the engine and rapid acceleration. Effect on carbon monoxide emissions for 3, 4 and 5 hole nozzles are shown in Figure 9. Effect on HRR for Blend.  Figure 13 to Figure 14 respectively. By relating the graphs, it is found that for 4 hole nozzle due to thoroughness in the fuel and air mixing the CO emission is prominently lowered with diesel, RSME and B20 blend.  Figure 11. Variation of pressure for Biodiesel.

Hydrocarbon emission
Hydrocarbon emissions are the source of unburned fuels that impinge on to the cylinder wall. The HC emissions are due to lean mixtures, in lean mixtures the flame speeds might be too little for combustion and causes wall quenching. When the unburnt fuel burns in the successive cycle it will produce HC emissions. Effect on HC emissions for 3, 4 and 5 hole nozzles are shown in Figure 16 to Figure 18 respectively. From the graphs it is evident that HC formation is considerably decreased with 4 hole nozzle with diesel, RSME and B20 blend because it will produce high flame speeds for better turbulence.

Oxides of nitrogen (NOx)
The volume of NOx formed is due to the peak temperature reached in the cylinder, oxygen concentrations, and residence time. The large amount of NOx is formed during the early stage of the combustion, when the piston is motionless close to the top of its stroke. At this stage the  temperature of the flame is at its peak. Effect on NOx emissions for 3, 4 and 5 hole nozzles are shown in Figure 19 to Figure 21 respectively. From the graphs it is observed that NOx emission increases with 4 hole nozzle this is owing to the complete combustion of air and fuel. Figure 13. Effect on CO for Diesel. Figure 14. Effect on CO for Biodiesel.

CO2 Emissions
During combustion the hydrocarbon fuel burns with air to liberate heat energy, in this process the carbon in the fuel reacts with oxygen in the air to produce carbon-dioxide as a by-product. The carbondioxide emissions are the source of the complete combustion. Effect on CO2 emissions for 3, 4 and 5 hole nozzles are shown in Figure 22 to Figure 24 respectively. From the graphs it is seen that the 4 hole nozzle produces high CO2 emissions, hence the 4 hole nozzle generates complete combustion in the CI engine as compared with the 3 and 5 hole nozzle for all the fuels tested.   Figure 16. Effect on HC for Diesel. Figure 17. Effect on HC for Biodiesel.

Conclusion
The combustion, performance and emission characteristics of a single cylinder diesel engine is studied by varying the number of injector nozzle hole The 0.25 mm diameter hole injector is selected and the number of holes is varied to 3,4 and 5. Tests are done with diesel, RSME and B20 blend, from the  10 results observed it is determined that 4 hole nozzle generates encouraging results concerning engine performance, combustion and emission compared with the other two nozzles for all the fuels used. The major drawback is that increase in NOx and CO2 emissions were observed for all the tested fuels. The 3 hole and 5 hole nozzle gives higher CO and HC emissions whereas NOX is reduced due to lesser heat release rate and improper mixing of air and fuel.