Operating Range of Low Temperature Diesel Combustion with Supercharging

Low temperature diesel combustion with a large amount of exhaust gas recirculation in a direct injection diesel engine was investigated. Tests were carried out under various engine speeds, injection pressures, injection timings, and injection quantities. Exhaust emissions and brake specific fuel consumption were measured at different torque and engine speed conditions. High rates of exhaust gas recirculation led to the simultaneous reduction of nitrogen oxide and soot emissions due to a lower combustion temperature than conventional diesel combustion. However, hydrocarbon and carbon monoxide emissions increased as the combustion temperature decreased because of incomplete combustion and the lack of an oxidation reaction.

To overcome the operating range limits of low temperature diesel combustion, increased intake pressure with a modified turbocharger was employed. As a result of adopting increased intake pressure in low temperature diesel combustion, wider operating range was achieved compared with naturally aspirated condition. This is because relatively complete combustion occurred because of more air utilization under these conditions. Moreover, increased intake pressure resulted in lower hydrocarbon and carbon monoxide emissions due to a higher oxygen rate, which induced higher combustion temperatures. The effect of increased intake pressure on nitrogen oxide emission was found to be negligible. In contrast, soot emission was significantly reduced when intake pressure was increased.