Ignition quality and composition of fuel volatile fraction: Effects on diesel combustion

An experimental study was conducted to discern the nature of the mixture formation process in high and low swirl direct injection diesel engines. The study focussed on the order of fuel component vaporization and burning. These tests were motivated by reports of distillation-like droplet vaporization in out-of-engine experiments. The principal parameters varied were ignition quality and aromatics content of the fuel volatile fraction, and swirl ratio. The effect of fuel sulfur-bearing component volatility on exhaust smoke was investigated.; Two sets of fuels were used to test fuel physical and chemical property effects. One fuel set was blended to have smooth boiling curves and bulk properties like typical D-2 fuels, but with modification of volatile fraction ignition quality and aromatics content. The second set had a radically changed volatile fraction ignition quality. This set consisted of D-2 fuels blended with n-octane, a volatile, high ignition quality hydrocarbon. These fuels did not have smooth boiling curves. The sulfur study used a D-2 fuel doped with two sulfur-bearing hydrocarbons of different volatilities.; The experimental data included cylinder pressure, gaseous emissions, and smoke; it showed that ignition delay and emissions were insensitive to the fuel volatile fraction changes of the smooth boiling fuels in both engines. The low swirl engine was relatively insensitive to the changes of the n-octane blends. The ignition delays of the smooth boiling fuels correlated well with cetane number. This was not always true for the n-octane blends. Comparisons of smoke for the sulfur-doped fuels in the low swirl engine showed that fuel sulfur does change smoke. The more volatile dopant changed smoke more.; The bulk fuel cetane number is a valid indicator of ignition quality for the smooth boiling fuels set. The volatile fraction ignition quality is not disproportionately significant. Mixture formation was found not to be governed by fuel volatility. The order of fuel component vaporization was not rigorously determined, and will likely not be determined with this methodology.