Comprehensive Correlation for the Prediction of the Heat Release Characteristics of Diesel/CNG Mixtures in a Single-Zone Combustion Model

Abstract

Fuel combinations with substantial differences in reactivity, such as diesel/CNG, represent one of the most promising alternative combustion strategies these days. In general, the conversion from diesel to dual-fuel operation can be performed in existing in-use heavy-duty compression-ignition engines with minimum modifications, which guarantee very little particles, less nitrogen oxide (NOx), and reduced noise by half compared to diesel. These factors make it feasible to retrofit a CNG fuel system on an existing diesel engine to operate it in dual fuel mode. However, the single-zone combustion models using the traditional single-Wiebe function are exceptionally adopted to assess the dedicated dual fuel engines, whereas the heat loss to the walls is estimated by using the Woschni heat loss formulation. It means that the fast and preliminary analysis of the unmodified engine performance by 1-zone models becomes complicated due to the obvious deterioration of the energy parameters, which, in turn, was predetermined from the deviation in the thermodynamic cycle variables as the calculation outcome. In this study, the main novelty lies in the fact that we propose a novel composition-considered Woschni correlation for the prediction of the heat release duration characteristics of diesel/CNG mixtures for the unmodified diesel engine. The elimination of former deficiencies distinctive to a single-zone thermodynamic model by applying the interim steps described became the core of the research presented in this paper. It led to successful derivation of the necessary correlation for modelling the heat release duration characteristics of an ICE operated in the dual fuel mode.