Analysis of Compressed Natural Gas Burn Rate and Flame Propagation on a Sub-Compact Vehicle Engine

摘要

In terms of sub-compact cars using alternative fuels, the vehicle characteristics areudgoverned by the engine operation. The main focus of this paper was to evaluate a subcompactudcar engine on its performance and burn rate of gasoline and compressed naturaludgas (CNG) . A bi-fuel sequential system was used for this evaluation. Measurements ofudengine speed, torque and fuel were done on an eddy current dynamometer, whileudmeasurements of in-cylinder pressure, crank angle and spark were analyzed from resultsudtaken by a data acquisition system. The emissions readings were also compared using anudemission analyzer. The results were analyzed for burn rate based on the first law ofudthermodynamics. A 3-dimensional computational fluid dynamics (CFD) model wasuddone to estimate the flame speed. The comparison shows an average drop of 18.6% forudthe power, 7% for brake specific fuel consumption (BSFC) and the efficiency loss wasud17.3%. Pressure analysis shows peak pressure dropped by 16%. The burn rate showsudwhy CNG had a slower burning speed on the small engine. CFD predicted the flameudpropagation speed at 8.45 m/s. The engine speed of 4000 rpm at maximum brake torqueudproduced the results nearest to those for gasoline. In conclusion, volumetric losses andudCFD errors slightly reduce the accuracy of the results, but nevertheless an 8.45 m/sudflame speed was estimated.