An investigation of injection rate controlled heat release of selected alternate fuels in a direct injection diesel engine

An in depth investigation of rate controlled heat release of selected alternate fuels in a direct injection Diesel engine is described. In addition to Diesel No. 2 fuel which was used for baseline comparison, the low cetane fuels tested in the study were a high volatility - low viscosity fuel (Type I referee), and low volatility - high viscosity fuel (Type II referee), and high octane gasoline. Two different models were developed to give some insight into the various physical processes that take place when heat release of the fuel is controlled by rate of injection. The results of a droplet ignition delay model showed that the zone of combustion due to ignition of a pilot fuel spray must grow to a distance of 55 nozzle diameters in order for rate controlled combustion to occur. The results of a flame speed model showed that the combustion zone must grow to a distance of at least 30 nozzle diameters for rate controlled combustion to occur. Using the split injection timing of 21{dollar}spcirc{dollar} bTDC for the pilot spray and 8{dollar}spcirc{dollar} bTDC for the main spray predicted by theory resulted in the successful occurrence of rate controlled heat release for all of the fuels tested in the study. Since the fuels tested bracketed a broad spectrum of fuels on the distillation curve, the use of rate controlled combustion with other low cetane fuels within these limits should extend their use in the Diesel engine. All of the fuels tested were compared on a common basis in order to compare the relative effects of rate controlled heat release. All of the comparative results were obtained at the condition of 500 rpm, and heavy load.; The highest maximum rates of heat release were obtained with the high volatility fuels (gasoline and Type I), and the lowest maximum rates of heat release were obtained with the low volatility fuels (Type II and Diesel No. 2).; From the rate of heat release diagram it was noticed that the rate of heat release for the two high volatility fuels was relatively greater than the heavy fuels, and occurs later in the cycle. (Abstract shortened with permission of author.)...