Exhaust gas recirculation study on dual-fuel methane combustion

Abstract

Currently, interest in different alternative transport fuels is growing. There are two main reasons for this motivation: the universal environmental concern, caused by the noticeable impact of petroleum fuels on the human health and environment, and the necessity of replacement due to the declining availability of petroleum.

Dual-fuel engines could mean a partial solution of these worries, since the primary fuel of this type of engines is natural gas, mostly formed by methane, which can derived from both renewable and fossil sources. Diesel consumption is reduced by the introduction of some gas fractions, and dual-fuel mode allows, mainly, fewer greenhouse gas emissions.

From the economic and environmental point of view, dual-fuel is, thus, highly desirable. However, from a technical standpoint, this technique has been proved to be difficult to realize and optimize. Therefore, this master’s thesis has the objective to serve as a support on dual-fuel research field, as far as the Exhaust Gas Recirculation (EGR) effect on combustion and emissions performance is concerned.

Emphasis on the thesis was set, thereby, on the EGR rate variation effect on different engine parameters, such as lambda, cylinder pressure, exhaust gas temperature, charge air temperature, heat release rate (HRR), cumulative heat release rate (HR) or ignition delay, as well as on the NOx, THC and CO emissions performance.

Based on the results of this master’s thesis it can be concluded that EGR rate raises lead on significant reduction of NOx emissions, as well as a slightly decrease of unburned hydrocarbons. CO emissions are not influenced at low EGR rates, performing a sudden increase for the highest ones, around 25-30%. At the same time, combustion efficiency seems to decline with EGR, as seen from HR curves and CO emissions, obtaining extremely rich mixtures.