Effects of high intake-air temperature on emission characteristics under constant charging efficiency

Abstract The purpose of study is to analyze effect of intake air temperature in accordance with injection timings on combustion and emission characteristics. The operating conditions were fixed engine speed was 1800 rpm, and injection quantity was 17 mg. The injection timing was advanced from BTDC 6° to BTDC 24° at intervals of 3°. When the intake air flow rate was fixed before controlling intake air temperatures, the charging efficiency did not change with intake air temperature. Hence, the effect of only the intake air temperature was analyzed. When the intake air temperature was 100 °C compared to 20 °C, the IMEPnet increased by about 14.5% (0.55 MPa → 0.63 MPa) at the optimum injection timing (BTDC 6°, 9°). Because this high temperature reduced the ignition delay and advanced the ignition timing close to the TDC resulting in reducing negative work. In addition, the difference in NOx emission for different intake air temperatures was insignificant. When the intake air temperature was 100 °C compared to 20 °C, the high intake air temperature reduced the emissions of THC by about 41.3% (0.196 g/kWh → 0.115 g/kWh) and nanoparticles by about 60.5% (1188 μg/m3 → 468.6 μg/m3) by improving the evaporability of the fuel. In addition, carbon monoxide (CO) emissions decreased by about 45.3% (3.86 g/kWh → 2.11 g/kWh) in the case of 80 °C compared to 20 °C. Thus, the increase in the intake air temperature under constant intake air mass flow rate improved the combustion efficiency and reduced emission of THC, CO, and nanoparticles without increasing NOX emissions.