Examination of Effective Rates of Combustion Heat Release in a Dual-Fuel Engine

Abstract

The combustion processes in a dual-fuel engine are examined through the computation and analysis of effective rates of heat release. Methane was adopted as the primary fuel and the effect of deliberately introducing carbon dioxide along with the methane was also examined to simulate operation on methane sources containing carbon dioxide as a major contaminant. An examination of the various heat release records suggests that dual-fuel combustion generally appears to undergo two distinct phases. The first phase is associated mainly with the consumption of the pilot and some associated gaseous fuel, while the second phase is dependent on the concentrations and the quality of the gaseous fuel employed. Under light audible knock, the first phase gets prolonged and persists over a much longer period than under knock-free combustion. The rates of burning are excessively high and project well over the second phase. This is indirectly indicative of the auto-ignition nature of knock and the simultaneous rapid burning of the pilot together with a very substantial fraction of the gaseous charge.