A second law-based framework to identify high efficiency pathways in dual fuel low temperature combustion

While dual fuel low temperature combustion (LTC) has been studied before, a detailed second law analysis of dual fuel LTC is not yet available in the open literature. To address this gap, a previously validated, closed-cycle, multi-zone, simulation of diesel-natural gas dual fuel LTC was used to perform a second law analysis. For the present study, a 2.4-1 single-cylinder research engine operating at a nominal load of 6 bar BMEP and 1700 rpm was used. Zone-wise thermodynamic irreversibilities as well as total cumulative entropy generated and lost available work over the closed cycle were quantified. Subsequently, two convenient second-law parameters were defined: (1) the "lost available indicated mean effective pressure" (LAIMEP), which can be interpreted as an engine-size-normalized measure of available work that is lost due to thermodynamic irreversibilities (analogous to the relationship between indicated mean effective pressure and indicated work); (2) fuel conversion irreversibility (FCI), which is defined as the ratio of lost available work to total fuel chemical energy input. Finally, parametric studies were performed to quantify the effects of diesel start of injection, intake manifold temperature, and intake boost pressure on LAIMEP and FCI. The results show that significant entropy generation occurred in the flame zone (52-61 percent) and the burned zone (31-39 percent) while packets account for less than 6 percent of the overall irreversibilities. Parametric studies showed LAIMEPs in the range of 645-768 kPa and FCIs in the range of 32.8-39.2 percent at different engine operating conditions. Although the present study focused on dual fuel LTC, the conceptual definitions of LAIMEP and FCI are generally applicable for comparing the thermodynamic irreversibilities of IC engines of any size and operating on any combustion strategy. (C) 2017 Elsevier Ltd. All rights reserved.