Transient Emission Characteristics of a Light Duty Commercial Vehicle Powered by a Low Compression Ratio Diesel Engine 2021-01-1181

Adopting a low compression ratio (LCR) is a viable approach to meet the stringent emission regulations since it can simultaneously reduce the oxides of nitrogen (NO_x) and particulate matter (PM) emissions. However, significant shortcomings with the LCR approach include higher unburned hydrocarbon (HC) and carbon monoxide (CO) emissions and fuel economy penalties. Further, poor combustion stability of LCR engines at cold ambient and part load conditions may worsen the transient emission characteristics, which are least explored in the literature. In the present work, the effects of implementing the low compression ratio (LCR) approach in a mass-production light-duty vehicle powered by a single-cylinder diesel engine are investigated with a major focus on transient emission characteristics. The experimental investigations were conducted in a chassis dynamometer with the stock compression ratio of 18:1 followed by the reduced compression ratio of 14:1, and the results are quantified for the regulatory modified Indian drive cycle (MIDC). The results obtained show that the LCR approach led to a significant reduction of 25% and 72% in NO_x and PM emissions, respectively, along with increased HC and CO emissions by 10 and 2 fold. Further, there is a fuel economy penalty of up to 11.7% during the overall cycle. The HC, CO, and fuel economy penalties are extremely high in the initial phase of the MIDC cycle when the engine is not warmed up. The HC and CO emission penalty could be contained to 96% and 54%, respectively, by optimizing the injection settings. Moreover, the fuel economy penalty could also be reduced to 3.5%. The reasons behind the investigated single-cylinder diesel engine's transient emission and fuel consumption trends operated in the MIDC cycle are discussed in detail.