Effects of insulation on exhaust temperature and subsequent SCR efficiency of a heavy-duty diesel engine

Ammonia/urea selective catalytic reduction (SCR) is an efficient technology to control NOx emission from diesel engines. One of the critical challenges of SCR systems is its lack of catalytic activities in low temperature conditions such as cold start or warm-up periods. In this study, the effect of pipe insulation on the reduction of exhaust temperature drop was experimentally investigated based on dynamometer tests with a heavy-duty non-road diesel engine. The temperature drop of exhaust gas was measured with and without applying pipe insulation. Measurement results revealed that the effect of insulation on the mitigation of temperature loss becomes significant as engine brake power decreases. Thus, it is expected that the need for pipe insulation would be increased to keep SCR deNOx efficiency high, especially at low temperature conditions. Also, this study carried out numerical simulations to quantify the impact of pipe insulation on NOx conversion efficiency of a commercial SCR catalyst over a scheduled non-road transient cycle (NRTC) mode. Under the current heavy-duty non-road engine and SCR conditions, the application of pipe insulation would reduce 19.5 % of total cumulative tail-out NOx emission over NRTC hot mode. These results led to the cycle-averaged SCR efficiency of 98.2 % for 'with insulation', while it was predicted to be lowered to 97.6 % for 'without insulation'.