EFFECT OF NOZZLE HOLE AND PUMP PLUNGER DIAMETERS ON PERFORMANCE AND EMISSIONS OF DIESEL ENGINE M. S. SHEHATA Assistant Prof., Mechanical Engineering Technology Department, Higher Institute of Technology, Benha University. Egypt.

and S. M. ABDEL – RAZEK Dr., Department of Industrial Engineering, Faculty of Engineering, Misr University for Science and Technology, 6 October City, Egypt

Abstract An Experimental study is carried out to investigate the effect of fuel nozzle hole diameter and fuel pump plunger diameter on performance and exhaust emission for high duty six cylinders direct injection (DI) diesel engine. Two fuel nozzle diameters of 0.25 & 0.3 mm and two fuel pump plunger diameters of 10&12mm are varied during experimental work. CO, NOX, unburnt hydrocarbon (HC), exhaust smoke, exhaust gases temperature, engine torque, engine speed are measured, brake thermal efficiency and brake specified fuel consumption (BSFC) are calculated, all at different engine loads and different engine speeds. The study shows that decreasing nozzle hole diameter decreases exhaust smoke, HC, CO emissions and (BSFC) while increasing NOX emission, thermal efficiency, and exhaust gas temperature. Also higher NOX concentrations and lower smoke levels in engine exhaust emissions, with the increase of injection pump plunger diameter. The optimal fuel nozzle and fuel pump plunger design would be one that provided the maximum number of droplets liquid fuel burn in combustion chamber and minimum number of droplets liquid fuel unburned. The present study contributes in relating the specifications of fuel system and fuel injection parameters with performance parameters and pollutants emissions from DI diesel engines at different operating conditions. It is also necessary for further development and decreasing running cost of high duty diesel engines. Keywords (nozzle hole diameter, plunger diameter, emissions, performance, diesel engine)

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1. Introduction The diesel engine combustion process contains four distinct phases: ignition delay, premixed burn, controlled burn and late burn. The ignition delay is the time between injection and start of combustion. Fuel injected during the ignition delay will evaporate and mix with air. The rapid combustion of the evaporated fuel is called premixed burn. The high rate of heat release is causing high rate of NOX formation. Fuel injected after the premixed burn, will burn as soon as it mixes with air. The late burn is very much like the controlled burn; only the heat release will decrease because of a deteriorating fuel/air mixing. Atomization and penetration are two main parameters in development combustion in diesel engine cylinder. Penetration indicates how far the droplets enter the cylinder, this is important in respect of the fuel/air mixing rate. Spray tip penetration is one of the important factors to decide the combustion chamber size in diesel engine. An increase in nozzle diameter results in an increase of spray tip penetration. The initial spray tip penetration after start of injection increases sharply and then increases smoothly with time. The level of atomization determines the size of the droplets. Every injection parameter (injection pressure, injection timing and nozzle geometry) affects the atomization and penetration of the diesel fuel jet and thereby affecting the combustion process and the pollutant formation. For direct injection diesel engine performance, efficiency, and pollutant emissions have a strong dependence on the characteristics of the fuel injection process. Nowadays, the amount of fuel injection is not the only relevant characteristics of the injection process. The instantaneous fuel mass flow rate introduced into the combustion chamber, the evolution of the spray, and its interaction with the air is also important (Nishimura et al., 1998), Singh et al., 2003). One important phenomenon in this process is the flow behavior across the injector nozzle which is recognized as being influential on the fuel spray characteristics such as the spray tip penetration, spray angle and spray droplet sizes. Significant factors which affect spray characteristics are: fuel injection pressure, injection timing, nozzle configuration, fuel pump plunger diameter, ambient conditions, fuel properties, and fuel/air mixing (Arcoumanis et al., 1997; Macian et al., 203). Since there is a strong relation between pollutant emissions, engine operating conditions, injection system parameters, and other variables, several studies have been carried out with the aim of investigating the effect of these parameters separately or in combination (Russell et al., 1990; Uudogan et al., 1996). Abdel Razek (2007) studied the effect of fuel injection pressure and injection timing on engine performance, He found that increased injection pressure decreased brake specific fuel consumption (BSFC) and exhaust smoke levels while increased NOX emissions. Retarded injection timing, increased (BSFC), smoke intensity, and decreased NOX emissions. Shimada et. al. (1995) increased injection pressure by modifying the injection rate of the fuel pump and the nozzle area. They concluded that smoke and fuel consumption increased noticeably at low and medium pump speeds. Spray penetration at the end of injection extended and the fuel/air mixing improved. The same effect was also studied by (Chang et. al., 1995) they compared the particulate emissions for an engine equipped with injectors with different nozzle geometries under high injection pressure (up to 160 Mpa ) with the same rate of fuel injection. Particulate emissions for a rounded-edged inlet nozzle were much higher than that for a sharp-edged nozzle for similar injection rates and injection times. Su et. al. (1995) used spray visualization to study the effect of high pressure diesel injection. They found that for the same injection delivery, the sharp-edged inlet injector needed a higher pressure to over come the friction loss, but it produced a longer spray tip penetration length, a larger spray angle, and smaller Sauter Mean Diameter (SMD). For the same injection pressure, the sharp-edged inlet tip needed longer injection duration to delve the same mass of fuel than the round-edged inlet tip. At equal pressures to rounded-edged tips, the SEI tip produced larger overall average SMD droplets. Dodge et. al. (1992) investigated the effect of hole shapes on steady sprays. Twelve different hole shapes, with identical L/D ratio were studied. The results

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showed little effect of the hole shape on the fully developed downstream spray cone angle or droplet size distribution. Injection pressure had little effect on the spray shapes, while increasing pressure reduced droplet sizes modestly. Cheolwoong et al. (2004) studied the effects of multiple injections in a HSDI diesel engine. Thy concluded that, the combination of higher fuel injection pressure with smaller nozzle size is to be very effective in reducing particulate matter (PM) emission. Such advantages may originate from a better air-utilization due to improved spatial distribution, enhanced atomization and turbulence generated on periphery area of the spray caused by higher injection velocity (Dodge et al., 2002). Greeves and Tuilis (1993) found that for the same injection timing and engine load, the particulate reduced by 72% and NOX concentration increased by 20% when reducing the nozzle hole diameter from 0.24 to 0.2 mm, at constant injection delivery. The aim of the present work is to investigate the effect fuel nozzle hole diameter, and fuel pump plunger diameter on performance parameters and exhaust emission characteristics for DI diesel engine operates at different engine loads and speeds.

2. Experimental Setup The present study is conducted on the engine test cell of the Military Research Center, Egyptian Army, in the Research Labs. The experimental setup includes a heavy duty direct injection diesel engine and all instrumentation necessary for measuring the engine performance as well as its emission behavior is shown in Fig.(1). The engine used is six cylinders, in line, water cooled, heavy duty, direct injection four strokes diesel engine, with 150 & 147 mm bore and stroke respectively, with compression ratio 15: 1 and the rated output power is 300 bhp at 1800 rpm. Engine coolant temperature is controlled by heat exchanger tower system which is designed to thermostatically set and hold specified coolant outlet temperatures. All engine fluid temperatures are monitored using K-type thermocouples. The engine has provisions for varying fuel injection timing. A cradle for supporting the engine is of rigid design, adequately bolted to suitable foundations in correct alignment with the dynamometer; this assists steady running and the elimination of vibration. External loading is carried out by a Froude hydraulic dynamometer (type D. P .Y); a cardan shaft with two universal joints and of a design which prevents whirling is provided to connect the dynamometer to the engine. The fluid used is water with which the maximum braking power could reach 500 bhp at 3500 rpm. Engine torque is measured at the dynamometer with a mechanical scale. The dynamometer is claimed to be accurate to within ± 0.025% of nominal rating. An open volumetric measuring system is used for determining the fuel consumption of the engine during tests. It consists of calibrated glass cylinder connected with the fuel supply system of the engine and with a fuel tank by means of a two way cock. During the test, the cock can be set into three possible positions and allows feed fuel from tank or from the calibrated cylinder of accurately known volume. By recording the time of consumption of that volume, the fuel consumption per hour is calculated. All of the air to be delivered to the engine is metered by steady state air flow meter located up stream of a surge tank. A thermocouple type K with a special multi channel amplifier is used to measure the exhaust temperature Texhaust (just before the entry to the turbine). All the above temperatures are measured on specially matched sets of calibrated thermocouples. Engine speed (rpm) was measured by toothed gear and magnetic pick up combination installed on the engine output shaft. All steady state reading of temperatures and engine speed for a particular test condition are fed into a computer controlled data acquisition and recording system. A test consoles as shown in Fig.(1b) contains the dynamometer controls along with, conventional gages for indicating engine oil pressure, engine speed, water pressure to and out the dynamometer, besides the temperatures of inlet and outlet water of the engine and the dynamometer, and exhaust gases temperatures in front of the turbocharger. An experimental program is carried out

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in order to study the effect of nozzle hole diameter and fuel pump plunger diameter on performance and exhaust emission characteristics of the engine when operated at different speeds and loads. Experiments have been performed at five engine speeds, namely, 1000, 1200, 1400, 1600 &1800 rpm with changing the load percent from 25% to 100% with increment 25% from full load. Emission measurements during each steady state test condition are obtained by sampling the exhaust gases from the chimney. Exhaust gases are analyzed for unburned hydrocarbon (HC), carbon monoxide (CO), nitrogen oxide (NOX), oxygen (O2), and carbon dioxide (CO2). Hydrocarbons are measured by a heated flame ionization detector (FID). Carbon monoxide and carbon dioxide are measured by non-dispersive infrared analyzer (NDIR). NOX is measured by Electro chemical gas analyzer and the measurements directly show on a digital display screen. Smoke levels are measured by the Hartridge MK3 smoke-meter. Because of the large number of test cases require for the study and to ensure repeatability and high degree of accuracy of the measurement in the experiments, certain equality routines are carried out. The emission analyzers underwent daily calibration procedures. To ensure repeatability a reference test case is measured prior to each new set of experiment in order to ensure similar behavior of the engine in terms of pollutants and also with respect to the various engine setting.

Fig. (1) Experimental set up and measuring devices

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3- Modification and Test Matrix For simplifying the experimental work of the present study, the used engine should allow changing the injector nozzle diameter and the injection pump plunger diameter with a minimum of effort. It is desired that such an engine could be modified using existing components and hence keep the development aspect of the experiment to a minimum. The availability of fuel injection components restricted the study to one change of nozzle and plunger diameter. The plunger diameter is changed by changing the element set in the fuel injection pump assembly. Care is taken in choosing the new element to have the same stroke length as the original equipment in order to avoid the spurious effects on the experiment. The number of holes and the hole diameter of the nozzle cannot be changed Independently and, therefore, two different nozzles having different combinations of hole diameter and number of holes but the same total orifice area. In this regard, attention is also paid for maintaining the other nozzle geometrical parameters such as sac chamber volume, needle lift, diameter-length ratio of the nozzle holes, etc., as constant. Both nozzles have 140 injection angle and sharp entrance. The engine was tested in its production configuration before any modifications are made to establish the base line levels of performance and emissions. To investigate the effects of nozzle hole size and plunger diameter on engine exhaust emissions and performance, two different diameters of nozzle hole, 0.30 mm (being the baseline), and 0.25 mm. While plunger diameters are 12mm (being the base line) and 10mm are used in this test. The experiments are conducted for the same injector pressure (220 bars) and static injection advance angle of 34 CA (BTDC). However the fuel chosen for the tests is diesel oil No. 2D. The experiments are conducted at four load levels, namely, 25%, 50%, 75%, and 100% of full load. For each load condition engine is run for at least 10 min. The experiments are replicated three times. For each load the experiment conducted at six engine speed levels, namely, 1000, 1200, 1400, 1600, 1800, 2000, rpm.

4. Results and Discussion The experimental efforts described above were an attempt to quantify engine performance and emissions associated with changing nozzle and plunger diameters at different engine operating conditions for locomotive diesel engine. Based on the laboratory testing performed, the following results can be expected as follows:

4.1 Effect of Nozzle Hole Diameter on Emissions and Engine Performance 4.1.1 HC Emissions The HC in the diesel exhaust consist of the original fuel molecules, partially decomposed fuel molecules and/or new compounds formed from recombined fragments. The heterogeneous combustion process in the diesel implies that many resources could control HC formation and oxidation. The conditions required for HC emissions are low local temperature or insufficient oxygen concentration. This can be achieved with mixtures of too lean or rich for fast combustion reactions. These conditions may be found: (i) In quench regions near the wall and/or piston in areas of wet fuel impingement on the walls, (ii) In the fuel rich spray core and tail, (iii) In the lean limit regions around the fuel spray jet and fuel issuing from the nozzle sac and hole volume. However with state of the art and fully developed DI diesel engine and fuel injection equipment, the two major sources of HC have been found to be the nozzle sac and hole volume, and regions where the fuel had mixed to leaner than the lean limit. In addition to the complex heterogeneous nature of diesel combustion, there are many possible processes which could control HC formation. HC can be emitted from mixtures exposed to high or low temperature of fuel rich conditions in a combustion system is entirely determined by the overall

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equivalence ratio and fuel air/mixing of injected fuel passing from the nozzle orifice through the combustion chamber. In particular, account must be taken of the mixing history. Figs. (2a &2b) show the effect of engine load and engine speed on HC emissions for two different nozzle hole diameters. HC concentration increases with the increases of nozzle hole diameter due to the effect of increased droplet size within the size distribution of the fuel spray. Large droplets can penetrate further in a cross stream air swirl than small droplets and may increase fuel concentration (in liquid or gaseous form) in the quench layer near the chamber wall. Also, a sufficient increase in droplet size may delay vaporization and gas phase fuel/air mixing. In the case of direct injection diesel engines under or over penetration of fuel spray leads to fuel rich mixtures in the inner or outer radii of the chamber, this reduces the gross rate of fuel/air mixing in respective fuel rich regions. However, when the nozzle hole diameter is decreased, the spray characteristics are affected as; (i) The spray tip penetration gets shorter which means less wall impingement and, (ii) The droplet size is decreased and hence better atomization, faster evaporating and mixing which leads to essential reduction in HC emissions. The mechanism of formation and oxidation of the hydrocarbon molecules depend upon most of the engine operating variables. An increase in load results in longer period of injection and more fuel is injected later in the cycle. In general this results in a shorter reaction time for the last part of the injected fuel. An increase in load also results lower excess oxygen concentration. These two factors tend to decrease the rate of elimination reaction. However, higher gas temperature is reached because of more fuel is burned and because there is a drop in the percentage of heat losses to coolant. This tends to increase the elimination reaction rate. At idling and light loads conditions, the fuel spray does not reach the walls and its concentration in the core is small. Under these conditions HC emissions originate mainly from lean flame out region and composed of the original fuel molecules because of the fuel molecules have little chance to decompose latter in the cycle due to the relatively low gas temperatures reached under light loads. The increase in local temperature of this region, due to subsequent combustion of the rest of the spry, is very small, and the elimination reaction rates are very slow. These reactions are further reduced because of the very low concentration of the fuel molecules as they diffuse in the air around this region. The ratio of the unburned hydrocarbon formed in this region to the total fuel injection is the highest at idling and this ratio decreases with the increase in load. At part loads, the increase in fuel/air ratio causes more fuel to be decomposed on the walls and produces higher concentrations in the spray core causing an increase of HC concentration in this region. However, there is sufficient oxygen in the mixture so, as temperature increases, the oxidation reactions are promoted and HC emissions are reduced. At high load, HC emissions originate from the fuel molecules in the core, and in the walls. Under these conditions, the temperatures reached in the cycle are fairly high and cause decomposition of some of the original fuel molecules. Since the fuel/air ratio in the spray core and near the wall is generally rich, there is a great possibility that some recombination reactions may occur between the hydrocarbon radicals and the intermediate compounds. This results in higher concentrations of the heavier hydrocarbon. It should be noted that at full load the molecules with 6 to 12 carbon atoms are reduced, but the molecules with 1 to 4 and 18 to 24 carbon atoms are increased. This implies that the medium size molecules are decomposed to lighter molecules and that the intermediate compounds are recombined to form heavier molecules. However as the engine load increases, heat release by the fuel also increase which improves combustion and consequently HC emissions level decreases. As shown in Figure 2a. As temperature level increases with engine speed due to reduce cooling effects, hydrocarbon does not follow the expected decrease with temperature due to improve oxidation, because of the offsetting factor of less time available. So, hydrocarbons, decreases with engine speed, as shown in Figure 2b. As engine speed increases HC concentration decreases due to turbulence intensity increases

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which improve mixing of burnt and unburnt gases and increase oxidation rate of different HC in engine cylinder. In the range of 25% to 50% load and also in the range of 1000 to 1400 rpm, the rate of HC decreasing is steeper with increase engine load and engine speed due to high rate of increasing gases temperature and high oxidation rates of different intermediate species of HC in engine cylinder.

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4.1.2 Smoke Emissions Rate of Fuel/air mixing process and injection timing have the most potential for controlling pollution formation. As fuel air mixing rate affects by both the injected fuel kinetic energy and the energy of the swirling air, so, mixing rate improves by improving methods of atomization, penetration, and air entrainment. Such methods increase injection pressure, injection rate, altered orifice size, or increase air swirl. Greeves and Tullis, (1993) report that increasing mixing rate due to air swirl or fuel injection rate resulting in reduced smoke and BSFC. Likely, the injection pressure, the injection period and the injection rate depend on the nozzle area. Maximum value of heat release rate of the first stage of combustion increases in response to the amount of fuel injected during the ignition delay period, i.e., in response to the nozzle area. The effect of nozzle configuration on the smoke can be explained by its effect on the rate of air entrainment. An increase in the air entrainment leads to lower local equivalence ratios in the richer zone of the fuel jet and will in addition be expected to the increase in the rate of intimate mixing (fuel vapor transport) in the fuel jets, will also reduce the equivalence ratios in the rich zone, and will increase the temperatures due to increase in the rate of heat release, results in reducing the amount of exhaust smoke. Smoke and BSFC decrease by decreasing nozzle hole diameter due to improve atomization and mixture formation which provides a rapid entrainment of oxygen into the spray as well as the more rapid heat transformation and results in lower exhaust smoke emission and reduces BSFC level as shown in Fig.(3). Engine speed has a profound effect on the degree of turbulence within the cylinder (Turbulence means all effects of mixing, macroscopic (air entrainment) and microscopic mixing of air and fuel) and on the reaction time available for combustion of carbon particles. Both these factors affect the eventual smoke levels in diesel engine. However, duration of fuel injection affects the amount of fuel injected after start of combustion and the extent of fuel burning which is approximated by an unmixed, diffusion flame. Therefore, duration of injection affects smoke characteristics. At constant fuel injection timing and air fuel ratio, as engine speed increases ignition delay and the percentage of fuel injected before ignition decrease, or as the amount of

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fuel unmixed diffuses, fuel burning rate increases, and thus increases engine smoke level. Figure 3 shows exhaust smoke emissions versus engine loads and speeds for two different nozzle diameters. The results show that exhaust smoke increases as the engine speed increases. At higher engine speeds, the time available for mixing and chemical reactions to take place is reduced. Thus carbon particles formed during the combustion process will have shorter residence time in which to mix and react with excess oxygen, causes more rich zones in the combustion chamber and increases smoke formation during combustion. Higher engine speeds favor shorter mixing and reaction times and higher smoke levels, while lower engine speeds favor longer mixing and reaction times and lower smoke levels. Meanwhile, the short time of expansion and exhaust processes at high engine speed restricts the oxidation of smoke in post flame zone and gives a high smoke level. Meanwhile, the smoke emitted at all engine loads, but the amount is usually increases with load as demonstrated in Figure 3.

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Fig.(3) Effect of Fuel Nozzle Diameter on Smoke Emission at Different Loads and Speeds 4.1.3 NOX Emissions

Figure 4 shows NOX concentrations versus engine load for different engine speeds with two different nozzle hole diameters. The effect of fuel nozzle diameter is mainly caused by a difference in fuel penetration. The nozzle of 0.25mm nozzle diameter has a slightly bigger injection surface causing a lower peak pressure and injection speed. The droplets from 0.25mm nozzle diameter have higher moment because of higher speed. A great momentum causes a deeper penetration and a better fuel distribution in the cylinder. This causes a large amount of

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fuel to ignite in the premixed burn and gives a steep rise in temperature. The evaporation of big droplets takes longer than for small droplets, also resulting in a larger ignition delay. Both effects will increase NOX formation. Smaller nozzle hole diameter produces shorter spray tip penetrations but wider spray angle, and also smaller overall average droplet sizes. Finer droplets mean better atomization and fuel/air mixing, which provides a rapid entrainment of oxygen into the fuel spray. Higher mixing rates results in high global heat release rates with high peak combustion temperature and higher NOX concentrations. The increase of NOX concentration with an increase in the engine speed is due to the combined effects of temperature, equivalence ratio and the time of burning fuel element burning (which is controlled by fuel/air mixing), where equivalence ratio and time of burning fuel element decrease with an increase in the engine speed. As engine speed increases, cycle time decreases, reducing time for heat loss which leads to increase wall temperature and inside cylinder air temperature. These lead to shorter ignition delays and increases rates of different reactions, results in high peak cylinder pressure and temperature and consequently increase NOX concentrations as shown in Figure 4 because of NO formation is more sensitive to gases temperature. NOX concentration increases with the increase of engine due to the increase of gases temperature. Temperature drops rapidly during expansion and exhaust strokes, but the reverse reaction or dissociation of NO is not rapid enough to establish equilibrium and therefore higher amount of NOX concentration appears in the exhaust at higher loads. The decrease in nozzle hole diameter could lead to efficient mixture preparation due to improved air utilization, which results in low exhaust smoke, HC and CO emissions. However, NOX emission increases due to the rise of the combustion temperature. 1600

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The most important part of the injection system is the fuel nozzle. The fuel is injected through the nozzle holes into the combustion chamber. The diameter and number of the nozzle holes depend on the amount of fuel that has to be injected, the combustion chamber geometry and the air motion inside the cylinder. The cylindrical hole produces the strongest cavitations and results in an increased spray break up with a larger spray divergence near the nozzle. The axis symmetric conical geometry suppresses cavitations by gradually reducing the effective cross sectional area along the hole. Decreasing the injector nozzle diameter is an effective method of increasing fuel air mixing during injection. Smaller nozzle hole diameter is found to be the most efficient at fuel/air mixing primarily because the fuel rich core of the jet is smaller. In addition, decreasing nozzle holes diameter causes a reduction in the turbulent energy generated by the jet. Since fuel/air mixing is controlled by turbulence generated at the jet boundary, this will offset the benefits of the reduced jet core size. Furthermore, jets emerging from smaller nozzle orifice diameter are not to penetrate as far as those emerging from larger orifice diameter. This decreases in penetration means that the fuel will not be exposed to all of the available air in the chamber. The optimal nozzle design would be one that provided the maximum number of liquid fuel burn in combustion chamber and minimum number of liquid fuel unburned

4.1.4 CO Emission

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Carbon monoxide concentrations for different engine loads and different engine speeds with two different fuel nozzle hole diameters are shown in Fig.(5a &5b). CO concentration decreases as fuel nozzle diameter decreases due to improve mixing process of fuel/air and improving atomization process. CO concentration decreases with the increase of engine load and engine speed due to increases gases temperature and turbulence intensity respectively. In the range of 20% to 50% load decreasing rate of CO concentration is steeper than at high load due to higher rate of gases temperature increases. On contrast, in range of 1400 to 1800 rpm decreasing rate of CO concentration is steeper than at low engine speed due to higher rate of turbulence intensity. CO concentrations are relatively low in diesel engine exhaust due to very lean mixture in diesel engine combustion. So any CO formation from diesel engine is due to incomplete mixing with combustion tacking place in locally rich conditions. In principle CO formation is strongly affects by uniformity of the air fuel mixture in the combustion chamber and the combustion temperature.

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At low load the quantity of fuel supplied is small, i.e., the mixture remains lean which produces less heat in the chamber resulting in low flame temperature consequently less conversion of CO to CO2. Beyond the rated load value, the percentage of CO in the exhaust increases due to deterioration of combustion process. For large nozzle hole diameter, after the start of injection, the liquid-phase fuel is surrounded with a number of flames into which the fuel is injected. During fuel injection, burned gas is entrained into the atomized fuel spray. The atomized fuel spray is lacking oxygen because the fuel injection entrains burned gas. As a result, combustion progress gradually, causing a relatively low peak of heat release rate. In this case the luminosity continued to increase even after diffusion combustion is nearly over. Before the appearance of blue flame during premixed combustion duration, the weak luminosity is carried out. The result showed increase in HC, CO exhaust smoke and reduction of NOX emissions compared to smaller nozzle hole diameter

4.1.5 Engine Performance Brake specific fuel consumption (BSFC) for different engine loads and different engine speeds with two different fuel nozzle hole diameters are shown in Fig.(6). BSFC increases with the increase of nozzle hole diameter due to the increase of amount of fuel injected and the increase the average of mean size diameter. At low engine load BSFC decreases with the increase of engine load up to 75% load where BSFC has minimum value for all engine speeds.

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At engine load above 75% load BSFC increases with the increase of engine load due high fraction losses. Also, at low engine speed up to 1400 rpm, BSFC increases with the increase of engine speed due to the increase of turbulence intensity which improves combustion quality and increases engine power. At high engine speed above 1400 rpm, BSFC increases with the increase of engine speed due to the increase of fraction losses which decreases engine brake power. It has been observed that smaller the nozzle diameter, the shorter the ignition delays. The smaller the nozzle diameter also improves the mixing, which is shown by shorter combustion duration. These results in decrease the heat and time losses, resulting in a higher thermal efficiency and lower fuel consumption. Brake thermal efficiency ηthermal for different engine loads with two different fuel nozzle hole diameters are shown in Fig.(7). Brake thermal efficiency increases with the decrease of nozzle hole diameter due to the increase of combustion efficiency and brake power at the same time the amount of fuel injected is decreased. As nozzle hole diameter decreases by 16%, brake thermal efficiency increases by 12 % at low load and by 20 % at high engine load. So the rate of increasing brake thermal efficiency increases with the decrease of nozzle hole diameter. Also, nozzle hole diameter has high effect at high engine load than at low load due to increase gases temperature and improving combustion quality Exhaust gases temperature Texh for different engine loads and different engine speeds with two different fuel nozzle hole diameters are shown in Fig.(8). Texh increases with the decrease of nozzle hole diameter due to improve fuel atomization, combustion quality, engine power and mixing process of burnt/unburnt gases which increase maximum gases temperature. Texh increases with the increase of engine speed due to increase heat release rate and reaction rate of different species with the increase of turbulence intensity result in engine speed increases. At low engine speed and low engine load, effect of engine speed on Texh is greater than effect of engine load. On contrast at high engine speed and high engine load effect of engine load on Texh is higher than engine speed due to higher gases temperature. Effect of nozzle hole diameter on increasing Texh with the increase of engine load is grater than with the increase of engine speed where engine load has higher effect on gases temperature than engine speed.

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4.2 Effect of Plunger Diameter on Emissions

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Fig.(9 a) Effect of Fuel Pump Plunger Diameter on NOX Emission at Different Loads and 1800 RPM Volume IV

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NOX (PPM)

NOX (PPM)

NOX and exhaust for different engine loads and different engine speeds with two different injection pump plunger diameters are shown in Fig.(9a&9b) and Fig.(10a&10b). In present study tests are conducted out with a two different fuel injection pump plunger sizes namely 10 and 12 mm diameter injection pump plungers with the same nozzle diameter, same fuel quantity per injection and the same nominal start of injection timing in each case. Lower NOX concentrations and higher exhaust smoke in engine exhaust are shown with the decrease of injection pump plunger diameter with the increase of engine speeds and engine loads due to injection greater mass of fuel during the ignition delay period. The effect of the larger mass injected during the delay period is to increase the proportion of pre-mixed burning. Change in injection pump plunger size gives rise to the changes in the quantity of fuel injected before start of combustion. For certain engine speed, the in cylinder air motion unchanged and the change is linked to injection effects. The volume of fuel injected during ignition delay as a useful parameter for controlling NOX formation and exhaust smoke from DI diesel engines. David el. al. (1995) studied the effect of injection rate shapes with DI diesel engine exhaust emissions with a number of different fuel injection pump plunger diameters (9,10&11mm), the results indicated that the changes in emissions levels can be explained in terms of variations in the instantaneous injection rate.

DPlunger=10 mm DPlunger=12 mm

70 60 50 DNozzle=0.25mm DNozzle=0.3mm

40 30 0

25

50 75 100 Engine Load (%)

125

90 80 70 60 50 40 30 20 10 0

Smoke HUS (%)

Smoke HUS (%)

80

1000

1200 1400 1600 1800 Engine Speed (RPM) Fig.(10 b) Effect of Fuel Pump Plunger Diameter on NOX Emission at Different Speeds and Full Load

Fig.(10 a) Effect of Fuel Pump Plunger Diameter on NO X Emission at Different Loads and 1800 RPM

At high engine load, for a given engine speed, there is a strong relation between NOX emissions and the volume of fuel injected during the ignition delay period where an increase in the injection kinetic energy gives a decrease in exhaust smoke. For different engine load, the percentage of NOX concentrations decreases by 19% with the decrease of pump plunger diameter by 16.6%. For different engine speeds NOX concentrations decreases nearly by constant value as injection pump plunger diameter decreases from 12 mm to 10 mm. The effect of injection pump plunger diameter on NOX concentrations for different engine loads is grater than for different engine speeds. The effect of decreasing injection pump plunger diameter on increasing exhaust smoke is nearly the same for different engine loads and different engine speeds. The higher injection fuel pump plunger diameter gives higher peak injection pressure and shorter injection duration, because more fuel is pumped through the same nozzle in a certain time frame. Because of the ignition delay for the low pressure is the same as high pressure, so more mass of fuel is injected by the high pressure during the same ignition delay, causing a more intense premixed burn, higher temperatures and more NOX is formed. Also, the pressure of injected fuel is main parameter for decreasing exhaust smoke as shown in Fig.(10a&10b).

5. CONCLUSIONS The combustion and emission formation in diesel engines is governed mainly by spray formation and mixing. Important parameters governing these are droplet size, distribution, concentration, and injection velocity. Smaller nozzle diameter are believed to give smaller droplet size, even with reduced injection pressure, which leads to better fuel atomization, faster evaporation and better mixing. Based on the experimental efforts, the test results are summarized as follows: 1. Smaller nozzle hole diameter contributes to a better air utilization, so both of HC concentrations, exhaust smoke, BSFC and CO concentrations are decreased, on contrast NOX concentrations, brake thermal efficiency and exhaust gases temperature are increased for different engine loads and engine speeds due to improve fuel atomization, fine fuel droplets, homogeneous mixture distribution, higher gases temperature, higher rate of reactions for different species and higher heat release rate. 2. As fuel pump plunger diameter increases NOX concentrations increases, on contrast exhaust smoke decreases for different engine load and engine speeds due to fuel is more breakup with increase injection pump plunger diameter which improves fuel atomization process and combustion quality. Also, the injection of a greater mass of fuel during the ignition delay period increases the proportion of premixing burning which increases NOX formation.

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3. Significant improvements in engine emissions and engine performance can be obtained if fuel nozzle hole diameter and injection fuel pump plunger diameter are optimized. 4. As fuel nozzle hole diameter decreases by 16%, brake thermal efficiency increases by 12 % at low load and by 20 % at high engine load. So, fuel nozzle hole diameter has high effect on brake thermal efficiency at high engine load than at low load due to increase gases temperature and improving combustion quality. 5. For different engine load, the percentage of NOX concentrations decreases by 19% with the decrease of pump plunger diameter by 16.6%. For different engine speeds, NOX concentrations decreases nearly by constant value as injection pump plunger diameter decreases from 12 mm to 10 mm.

REFERENCES 1. Abdel Razek, S. M., "The Effect of Fuel Injection Pressure and Timing on a Heavy Duty DI Diesel Engine Performance", Journal of Engineering and Applied Science, Faculty of Engineering, Cairo University, 2007. 2. Arcoumanis, C., Gavaises, M., and French, B. "Effect of Fuel Injection Processes on the Structure of Diesel Spray." SAE Paper, No. 970799, 1997. 3. Chang, C.T., Reitz, R. D., and Farrell, P. V., "Effects of Injection Pressure and Nozzle Geometry on Spray SMD and DI Emissions", SAE Paper, No.952360, 1995. 4. Cheolwoong Park, Sanghoon Kook and Choongsik Bae, “Effects of Multiple Injections in a HSDI Diesel Engine Equipped with Common Rail Injection System”, SAE Paper 2004-010127, 2004. 5. David J. Timoney and William J. Smith, "Correlation of injection rate shapes with DI Diesel Exhaust Emissions," SAE Paper No. 950214, 1995. 6. Dodge, L, G., Ryan, T. W., and Ryan, M,G., "Effect of Different Injector Hole Shapes on Diesel Sprays," SAE Paper, No. 920623, 1992. 7. Dodge L. G., Simescu S., Neely G. D., Maymar M. J., and Dickey D. W., Savonen C. L., Effect of Small Holes and High Injection Pressures on Diesel Engine Combustion”, SAE Paper 2002-01-0494, 2002. 8. Greeves, G., and Tullis, S., "Combustion of EUI-200 and Quiescent combustion system towards US 94 Emissions," SAE Paper No. 930274, 1993. .٩ Macian, V., Payri, R., Margot, X., and Salvador, F. J., "A CFD Analysis of the Influence of Diesel Nozzle Geometry on the Inception of Cavitations", Atomization and Sprays, 13(5), 579604, 2003. 10. Nishimura, T., Satoh, K., Takahashi, S., and Yokota, K., "Effects of Fuel Injection rate on Combustion and Emissions in a DI Diesel Engine", SAE Paper, No. 981929, 1998. 11. Russell, M. F., Young, C. D., and Nicol, S. W., "Modulation of Injection Rate to Improve Direct Injection diesel Engine Noise", SAE Paper, No.900349, 1990. 12. Singh, I., Zhong, L., Henein, N. A., and Bryzik, W., "Effect of Nozzle Hole Geometry on a HSDI Diesel Engine out Emissions", SAE Paper, No. 2003- 01-0704, 2003. 13. Shimada, t., Shoji, T., and Takeda, Y., "Effects of Injection Pressure and Nozzle Geometry on DI Diesel Emissions and Performance", SAE Paper, No. 950604, 1995. 14. Su, T. F., Farrell, P. V., and Nagarajan, R. T., "Nozzle Effect on High pressure Diesel Injection", SAE Paper, No. 950083, 1995. 15. Uudogan, A., Xin, J., and Reitz, R. D., "Exploring the Use of Multiple Injectors and Split injection to Reduce DI Diesel Engine Emissions", SAE Paper, No. 962058, 1996.

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