Development of a High-Power Density Diesel Engine with a Heat-Insulation Coating: Application of Ultrahigh-Pressure Fuel Injection

Thermal insulation coating is considered a low heat rejection technology for improving the thermal efficiency of engines in the future. A thermal-insulation-coated piston was used to reduce an engine's heat loss; however, the piston temperature was increased notably for high-power engines. This increased wall temperature causes burning of the diesel spray. In order to analyze and improve the combustion quality of a high-power engine compounded with a thermal-insulation-coated piston, experiments and simulation methods were used in this research. The ultrahigh-pressure fuel injection system (up to 250 MPa) was applied to study the effect on combustion under high wall temperature and high-power conditions. A high wall temperature environment combustion image was achieved by visualization experiment in the constant volume combustion bomb. The thermal-insulation-coating and high-power engine condition can lead to ultrahigh wall temperatures. To study this kind of high wall temperature environment, the constant volume combustion bomb model was founded and calibrated. The effects of ultrahigh-pressure fuel injection and spray impingement distance on the combustion of high wall temperature were studied. The simulation results showed that the ignition delay is shortened, leading to more soot and longer combustion duration, which caused the combustion deterioration. With an increased fuel injection pressure and longer impinging distance, the combustion was improved. Moreover, the effect of increasing injection pressure on combustion is more obvious.