Document Type : Original Article
Department of Mechanical Engineering, Faculty of Engineering, University of Mohaghegh Ardabili, Ardabil, Iran
The dependence of human beings on motor vehicles in their everyday life and the decrease of oil reserves all over the world have doubled the importance of attention to Spark Ignition (SI) engines. One of the most efficient ways to reduce fuel cost and knock intensity in SI engines is to use gasoline-Natural Gas (NG) dual fuel mixture. In the current study, 4 different combinations of gasoline and NG (with gasoline as the predominant fuel), namely G100 (100% gasoline), G87.5 (87.5% gasoline and the rest NG), G75 (75% gasoline and the rest NG), and G62.5 (62.5% gasoline and the rest NG) were investigated under stoichiometric conditions at the engine speed of 1800 rpm and the compression ratio of 10. The safe knocking limit was defined as the range with the knocking cycle percentage of lower than 5%. Then using the data obtained from the in-cylinder pressure of 400 consecutive cycles, the optimum spark advance was determined for each of the fuel modes. It was observed that the optimum spark advance based on indicated mean effective pressure (imep) fell in the non-knocking limit in all of the dual fuel modes. The analysis of the results indicated that as the fraction of NG in the dual fuel mixture increased, standard deviation (σ) and coefficient of variation (COV) of imep decreased. As for fuel economy, the results revealed that with the increase of NG fraction in the dual fuel mixture, the amount of the work generated per unit price increased significantly.