Effects of injection pressures on diesel combustion characteristics at low temperature combustion conditions in a constant volume combustion chamber

This experimental research seeks to explore how varying injection pressures impact the combustion characteristics of diesel fuel under low-temperature combustion (LTC) conditions. The experiments were carried out in a constant volume combustion chamber (CVCC) system equipped with a high-pressure common rail injection system. The ambient temperature of 800 K represents the LTC condition within the chamber, generated using a pre-combustion technique. The combustion pressure, heat release rate, and ignition delay were derived from the combustion pressure data recorded by a piezoelectric transducer sensor. The combustion characteristics of low-temperature conditions were compared with those of conventional diesel combustion engine conditions (1000 K) at high fuel injection pressures (800 bar and 1200 bar). The results indicated a higher maximum combustion pressure and a peak in the heat release rate under LTC conditions, primarily due to an extended ignition delay, which resulted in a greater accumulation and combustion of fuel during the uncontrolled combustion phase. However, the chemical combustion rate under LTC conditions deteriorates with increased fuel injection pressure, attributed to the longer liquid penetration length and higher latent heat effects of fuel vaporization. Therefore, reducing the injection pressure has significant potential to enhance combustion efficiency and shorten combustion duration, but it would also retard the combustion phase away from the start of injection.