Reduction of exhaust emissions and BSFC was studied for high pressure, wide range, and high EGR rates in a Super-clean Diesel six-cylinder heavy duty engine. The GVW 25-ton vehicle has 10.52 L engine displacement, with maximum power of 300 kW and maximum torque of 1842 Nm. The engine is equipped with high-pressure fuel injection of a 200 MPa level common-rail system. A variable geometry turbocharger (VGT) was newly designed. The maximum pressure ratio of the compressor is about twice that of the previous design: 2.5. Additionally, wide range and a high EGR rate are achieved by high pressure-loop EGR (HP-EGR) and low pressure-loop EGR (LP-EGR) with described VGT and high-pressure fuel injection. The HP-EGR can reduce NOx concentrations in the exhaust pipe, but the high EGR rate worsens smoke.
The HP-EGR system layout has an important shortcoming: it has great differences of the intake EGR gas amount into each cylinder, worsens smoke. The system layout can eliminate large differences of intake EGR gas amounts into each cylinder. The improved HP-EGR system layout achieves a wide range and high EGR more than the previous system. For engine speed of 1200 rpm and 40% load (BMEP0.83 MPa), the combined EGR of HP-EGR and LP-EGR can increase about twice EGR rate compared with the case of HP-EGR only and improve NOx to around half without BSFC deterioration. This system was evaluated practically to improve exhaust emissions in both steady-state and transient test conditions. Finally, the super-clean diesel engine is used with this system and checked experimentally using the JE05 transient test mode to meet the target performance.