Diesel has been used extensively as a fuel for small agricultural engines in many countries. As many gaseous fuels such as natural gas and LPG are available in abundance, a lot of interest is shown to substitute gas for diesel in these engines either partially or fully.
It has long been recognized that noise legislations have required the need for the development of quieter diesel engines. Although much emphasis has been given to automotive and large industrial engines, there is now also a growing interest in reducing the noise of small Diesel engines widely used in agriculture, portable and stationary applications.
In the present work, combustion noise, knock, and ignition limits data are measured and presented for a small diesel engine running on dual fuel of diesel and three gaseous fuels separately. The gaseous fuels used are liquefied petroleum gas, pure methane and compressed natural gas mixture. The maximum pressure rise rate during combustion is presented as a measure of combustion noise and the knocking and ignition limits are presented as torque output at the onset of knocking and ignition failure. Experimental investigation on the dual fuel engine revealed the noise generated from combustion, knocking, and ignition limits for all gases at different design and operating conditions.
A single cylinder small diesel engine is converted to run on dual fuel and equipped for combustion noise measurements and used throughout the work. The engine is fully computerized and the cylinder pressure data, crank angle data, engine operating variables are stored in a PC for off-line analysis. The effects of engine speeds, loads, pilot injection angle, pilot fuel quantity and compression ratio on combustion noise and knocking torque are examined for the dual engine running on the three gaseous fuels separately. The combustion noise, knocking and ignition limits, are found to relate to the type of gaseous fuels and to the engine design and operating parameters. The combustion noise emission from small diesel/dual fuel engine can be reduced by controlling the design and operating parameters of such engine.