EFFECT OF INJECTION SYSTEM PARAMETERS ON THE NOISE AND EMISSION OF A SMALL DI DIESEL ENGINE

Abstract

The overall contribution of fuel injection system on the total engine noise and diesel emissions is very small as compared to other operating and design parameters. But as new legislation with lower limit of noise and emissions are being enforced, the investigation of its effects on noise and emission has acquired greater importance. Noise is mainly generated by combustion, mechanical and inertia excitation and it transmits through the various components forming structure and airborne noises. Mechanical noise is generated by impacts caused by relative motion across the running clearance between two mechanical parts. Injection system is used to supply a metered quantity of fuel to the combustion chamber at predetermined rate and time. Injection system comprises elements starting from the fuel pump, fuel line up to fuel injection nozzle with system variables like nozzle opening pressure, plunger diameter and type, nozzle hole number, diameter and orientation and these have been selected as variable for the investigation. Using sound intensity technique of the noise source identification most dominating sources has been identified. Also it was observed that front end of the engine due to flywheel and fan produced the highest sound power level (95.3 dBA) and right and left sides generate almost the same sound power levels for deciding the microphone positions. Data for the response variables of engine noise, smoke and emissions have been selected different injection system parameters viz plunger type, number of nozzle holes and their diameter including orientation and nozzle opening pressure. The experiments have been performed for the different speed and load combinations. The data have been analyzed by OR-38 NVH analyzer. Nozzles having 3, 4 and 5 holes of diameters 0.25mm and 0.3mm have been used at different nozzle opening pressure in the experiments. The effect of nozzle opening pressure on smoke was found to be the highest. The responses of engine noise, smoke, CO, NOx and BSFC for different injection system parameters have been optimized using Taguchi's method with the help of a software "QUALITEK-4" (trial version). For the noise, speed was found the most dominating parameter while nozzle opening pressure influenced the exhaust emissions the most. BSFC was mainly influenced by the speed and the number of nozzle