A Comparison of Different Warm-up Technologies on Transient Emission Characteristics of a Low-Compression Ratio Light-duty Diesel Engine 2022-01-0482

It is well established that reducing the compression ratio (CR) of a diesel engine leads to a significant increase in hydrocarbon (HC) and carbon monoxide (CO) emissions, especially in cold and transient conditions. Hence, it is essential to find new strategies to reduce the HC and CO emissions of a low compression ratio (LCR) diesel engine in transient conditions. In the present work, a detailed evaluation of different warm-up technologies was conducted for their effects on transient emissions characteristics of a single-cylinder naturally aspirated LCR diesel engine. For this purpose, the engine was coupled to an instrumented transient engine dynamometer setup. A transient cycle of 160 seconds with starting, idling, speed ramp-up and load ramp-up was defined, and the engine was run in automatic mode by the dynamometer. The experiments were conducted by overnight soaking the engine at a specified temperature of 25 deg.C.

In the first step, the engine was tested with the stock compression ratio of 18:1, followed by the LCR configuration with the reduced compression ratio of 14:1. The results obtained show a multi-fold increase in HC and CO emissions with significant transient spikes. In the next step, the experimental investigations were continued in the LCR engine with different warm-up technologies viz., double glow plug (DGP), supercharger (SC), split cooling system (SCS) and secondary exhaust valve opening (SEVO). The transient emission characteristics of different technologies were compared with the baseline tests with the stock compression ratio, and the observed trends were analyzed. It was observed that the double glow plug approach is not very beneficial in containing the cold emissions as the HC and CO emissions of the LCR engine could be reduced only by 20 %. The split cooling system and SEVO approach were effective as they could mitigate the HC and CO emissions by 40 to 50 %. The introduction of a supercharger was the best approach to mitigate the cold and transient emissions of the LCR engine since it could reduce the HC and CO by more than 80%. Overall, the present study provides a relative comparison of different warm-up technologies in containing the transient emissions.