A study of gasoline lift-off combustion in a spark ignition engine

The aim of this study is to demonstrate the concept of gasoline lift-off spray combustion in which the burning velocity is controlled by the rate of mixture supply to the flame zone. With this concept, gasoline fuel is injected under high pressure to promote atomization, evaporation and mixing with the air, thereby quickly forming a homogenous mixture extending to the flame downstream of the spray. As a result, the injected fuel is burned sequentially. In this study, a constant-volume combustion vessel was used to visualize and analyze spray combustion. The experimental results made clear the effects of the initial conditions (e.g., injection pressure and nozzle hole diameter) and the ambient conditions (e.g., temperature and pressure) on the flame lift-off length and soot formation. In addition, the conditions facilitating this combustion concept were examined by conducting combustion simulations with the KIVA-3V code, taking into account the detailed chemical reaction mechanisms. Both the experimental and simulation results showed that the nozzle hole diameter and injection pressure are important factors for enhancing mixture formation rate in the spray and avoiding an over-rich mixture in gasoline lift-off combustion. Based on these findings, experiments were then carried out using a single-cylinder experimental engine. The results obtained under a limited condition of a single-hole nozzle spray confirmed that the combustion period can be controlled by means of the injection duration. It was also confirmed that sootless spray combustion was accomplished with little emission of unburned hydrocarbons.