Tong, L., Liu, H., Zheng, Z., and Yao, M., "The Design and Optimized Combination of Combustion Modesover Full-Load Range in a Multi-cylinder Light-duty Engine," SAE Technical Paper 2013-01-2623, 2013, doi:10.4271/2013-01-2623.
In order to achieve high efficiency and clean combustion indiesel engines, many advanced combustion concepts have been developed to simultaneously reduce NOx and soot emissions with high efficiency. However, the benefits of these combustion modes are limited to low loads because the energy release ratesaretoo fast at high loads. Recently, Dual-fuel highly premixed charge combustion (HPCC) strategies with the port injection of gasoline and direct injection of diesel have demonstrated advantages in terms of extending the operating range by the flexible control of fuel chemical reactivity and charge stratification. However, the extension to high-load in a turbocharged multi-cylinder diesel engine with the HPCC is a critical challenge due to excessive pressure rise rates. Mean while it suffers from the excessive of CO/HC emissions at low loads. Therefore, an effective optimization of combustion modes based on different operating conditions is very important for high-efficiency and clean combustion in diesel engines. In this work, experiments were carried out on a multi-cylinder turbocharged light-duty diesel engine equipped with a dual-fuel system to develop optimized combustion modes at different engine loads. The high pressure EGR (HP -EGR) and low pressure EGR (LP-EGR) systems were employed to ensure the damand of exhaust gases. Different combustion modes were investigated under the typical engine loads. The geometric compression ratio was changed to14:1 and the engine speed was set to 1900r/min. The results showed that, compared to HPCC mode, PCCI strategy reduced CO/UHC emissions and BFSC, while the NOx and soot emissions were similar to HPCC at the low load condition (0.25MPa BMEP). At the medium load conditions (0.59MPa and 0.85MPa BMEP), HPCC achieved the ultra-low NOx and soot emissions targets with improved BFSC, while additional LP-EGR was required as the BMEP exceeded0.85MPa. At higher load(1.05MPa BMEP), to suppress the rapid pressure rise rate, the in-cylinder late-injection and LP-EGR must be required. Additionally, by optimizing the turbocharger, the high load limit of HPCC mode was extended to 1.51MPa BMEP, thus achieving the full load of the original engine. Based on these results, experiments over a wide speed-load were conducted by the combination of optimized combustion modes. The results indicated that the diesel engine with hybrid combustion mode achieves ultra-low NOx and soot emissions and improved fuel economy over the full-load range compared to the original engine.