Exhaust gas recirculation in dual-fuel engine

Abstract

The efforts made during this thesis were pointed towards analyze and comprehend the effect promoted by exhaust gas recirculation systems within dual-fuel operation engines. The main outcomes of the study embrace the positive impact found in dual-fuel engines brought by low EGR rates regarding both thermal efficiency and exhaust emissions, as well as the effect promoted by changes of the methane share with respect the total amount of energy supplied.

The increase up to 50% of the diesel substitution rate leads to greater thermal characteristics, achieving higher cylinder pressure and cumulative heat release. Nevertheless, further increases of the methane share may produce significant reductions of the energy released associated to a poor combustion quality, as well as increase the likelihood of the onset of knocking.

The exhaust gas recirculation is mainly characterized by reductions of the oxygen content present within the intake mass flow. It is demonstrated how EGR rates below 15% bring notorious reductions of NOx without significantly compromising the thermal efficiency. Notwithstanding, when present to a large degree, the EGR may lead to erratic engine operation and, taken to the extreme, misfiring.