Abstract
In view of projected limitations on the availability of refined liquid fuels and the global increase in pollution from engines, there is an encouragement to researchers to look into other possible alternative fuels. Proven reserves of natural gas (NG) have been exploited in the past few years and, at the same time, there has been an increasing awareness worldwide of the resources available in other gaseous forms such as sewage gas, landfill gas and biogas. This has reactivated interest in the efficient operation of conventional internal combustion engines on gaseous fuels. Development of the gas-fuelled engine has a long history. The ad hoc nature of earlier applications did not create an adequate understanding of the combustion processes involved. There has recently been a revival, mainly as a result of small scale CHP. The dual-fuel engine, using liquid fuel in pilot injection to create conditions for ignition, involves more complex combustion conditions than the spark-ignited engine. Increasingly strict limits in many countries on pollutants from engines, especially particulates from diesel engines, have encouraged research into other possible benefits of alternative fuels. Stationary power plant would be the most obvious potential application as the large bulk of the storage required by gases is not usually a problem. The present research work concerns the use of gaseous fuels of varying quality representing a range of composition which may be encountered in gas from different sources. The total programme includes the effects of the quality, expressed as methane content, of the gaseous fuel and of the proportion of the pilot fuel injection over a range of speeds and loads, investigations into the performance parameters over a range of composition of gaseous mixture. A pair of 2-cylinder stationary type diesel engines, indirect and direct injection versions of the Lister Petter Alpha series, were used as the experimental facility for this work. The variation of quality was provided by mixing natural gas and carbon dioxide (CO2). Successful dual-fuel operation was carried out at two typical engine speeds - 2000 rev/min and 2800 rev/min and load 40 Nm (i. e. up to about 90% rated power) - for varying proportions of NG and CO2. Maximum NG substitution achieved in the IDI diesel engine was 60% and in the DI engine it was 80% and maximum CO2 added in the gas mixture was up to 67%, all limited by knock. CO increased with increase in NG substitution in both the engines but was not much affected by CO2 increase in the gas mixture. Peak pressure was affected by NG substitution in both the engines and sharper peaks were observed with addition in the gas mixture.