Performance evaluation of an engine-generator set operating on high butane content LPG fuel

Abstract

This paper presents the results of the performance diagnosis of a 6-cylinder engine-generator set, originally designed to run on diesel fuel or natural gas, operating in spark ignition mode and fueled with high butane content liquefied petroleum gas (LPG). In order to assess the steady-state and transient operation of the engine-generator, an original protocol for testing and recording of operating variables was designed, based on a stepped sequence of loads, comprising cold start, idling, operation at some mean load points and at a limited full load. During the tests, the variation of crankshaft rotational speed, warm-up time, engine temperatures, block vibrations, active/reactive power and engine-generator frequency, as well as exhaust emissions were continuously logged. The results show that, during the cold starting process, the engine is slow to reach nominal rated speed, its warm-up time is lengthy and its speed response during load transients is also sluggish, the latter being reflected in the voltage and frequency deviations of the output power; also, during transients, vibration levels are intensified, though the values are within the acceptable ranges according to the regulations. The torque performance of the engine-generator set is good when operating with LPG, satisfying the requirements for class G2 engine-generator units, but during transient processes it does not meet the specifications required for class G1, in terms of frequency and voltage deviations. In light of the emission limits suggested by the Environmental Protection Agency (EPA) for stationary units, it can be concluded that, without appropriate adjustments and regulations particular to LPG, the engine-generator set does not meet the carbon monoxide emission limits.