Abstract
The climate changes and increase in global temperature are the key factors that have mainly amplified the explo-ration studies of changing fuel injection and other constraints of compression ignition (CI) engines for the abatement of exhaust emissions. In current study, a direct injection (DI), CI engine was run on a test bench for the performance and emission analyses using different nozzles and injection timings. During the experiments, two types of nozzles known as sac and valve covered orifice (VCO) were used with hemispherical cavity and toroidal cavity pistons, respectively. Besides an already existing set of sac type nozzles, six distinct combinations of nozzles with varying cone angles and tip penetration (protrusion) lengths (designated as 135° × 3.5 mm, 140° × 3.5 mm, 145° × 3.5 mm, 150° × 3.5 mm, 150° × 2.5 mm, and 150° × 1.5 mm) were used at three different injection timings comprising 16° before top dead center (BTDC), 13°BTDC and 10°BTDC. Experimental results reveal that VCO nozzles in toroidal combustion chamber (CC) are better than sac nozzles with hemispherical CC, and that wider cone angle nozzles at 10° BTDC give the optimum results in terms of emissions and performance, relative to those of narrower cone angles. The 150° nozzles with 1.5 mm tip penetration give abated carbon monoxide (CO), hydrocarbon (HC) and smoke emissions along with better performance characteristics such as brake specific fuel consumption (BSFC) and brake power (BP), while exhibit slightly higher oxides of nitrogen (NOx) relative to other combinations. Moreover, the same combination also proves to be effective on emission control at 8 mode steady-state cycle.KEYWORDS: Compression ignition engine, regulated emissions, injector nozzle, tip penetration, injection timing1*Department of Mechanical Engineering, University of Engineering and Technology, Lahore 54000, Pakistan.INTRODUCTIONDuring the last couple of decades, the automotive sector has paid its attention on the improvement of advanced technologies related to emission control due to the escalating dynamic market trends for successfully reducing the emission problems along with better fuel economy. It is important to have an atmosphere within environmental standards for industries. For this purpose, different manufacturers and engineers are making their efforts to advance distinct strategies in operations for reduction in exhaust emission of petrol as well as diesel engine. Moreover, the automotive manufacturers have imposed strict standards related to emissions for making advance engine models to comply with them.Researchers are working hard for decreasing the harmful gases present in the exhaust of a diesel engine including the alteration in engine. The design of com-bustion chamber and injection nozzle for fuel spray are the two important parameters to decrease exhaust emission along with improved fuel economy. This is a very serious and challenging target for the automotive engineers to optimize the emissions with fuel economy and higher power.The geometrical parameters of injector nozzle have been reported to affect the transient behavior of fuel spray jet formation for various conditions of pressures such as needle opening, ambient pressure and injection pressure1,2. Also the spray patterns are directly influenced by different parameters for example the spray orifices and cone angles with their shape, length and diameter, the particular position of the fuel injector with respect to piston forming combustion chamber and lift of needle [3]. The formation of spray jet as well as its impingement depends on these designed variables which show their direct effect on exhaust of engine. The number of spray orifices that forms a jet is very important as for as air fuel mixture is concerned. There exists a direct relation between homogeneity of fuel-air mixture and number of orifices. The combustion process during such condition will produce less exhaust emissions1,3,4.