The Effects of Intake Throttling With Hot and Cold EGR in a CNG/Diesel Dual Fuel Engine

Abstract

Abstract Compressed natural gas (CNG)-diesel dual fuel engines produce lower emissions of nitrogen oxides (NOx) and particulate matter over conventional diesel engines. However, their major limitations are poor combustion stability at low and intermediate loads with high total hydrocarbon (THC) and carbon monoxide (CO) emissions. The limitations of poor combustion stability and high combustion by-products (THC and CO) emissions are exacerbated at high engine speeds. In this study, the authors attempt to reduce the THC and CO emissions at an intermediate load, corresponding to 6 bar gross indicated mean effective pressure (IMEP), at two engine speeds of 1500 rpm and 2800 rpm through intake throttling and using hot and cold exhaust gas recirculation (EGR) strategies in a CNG/diesel dual fuel engine. Experimental investigations are carried out at a 70% premixed ratio for the dual fuel engine. The results show that intake throttling has the potential to reduce THC and CO emissions by ∼37% and 15% at 1500 rpm and by ∼22% and 10% at 2800 rpm compared to the baseline dual fuel operation. However, NOx emissions increased as a trade-off. Further, implementing hot and cold EGR strategies to intake throttling, a significant reduction in NOx (∼72–78%) emission is observed, while THC and CO reductions are marginal at high speed. It is found that throttling the intake air in combination with hot EGR is more effective in reducing THC, CO and NOx emissions as compared to throttling with cold EGR strategy, while maintaining a similar power density as the baseline dual fuel engine.