Knock Reduction Measures in the Gas Fuelled Internal Combustion Engine

Abstract

Studies on the influence of applying various technologies for combustion knock reduction have been presented in the paper. Among others, investigation concerning the following: overexpanded cycle, variable valve timing, internal and exhaust gas recirculation, leaning the combustible mixture and cooling the incylinder charge were of the interest. The research works were focused on impact of these technologies on both knock intensity reduction, and engine performance and toxic emissions. Results presented in the paper were coming from experimental investigation based on incylinder combustion pressure data acquisition. Additionally, knock intensity calculation methods were discussed. They are based on incylinder combustion pressure pulsations. Combustion knock intensity expressed by the maximum peak of the in cylinder pressure pulsations shows a strong negative correlation with both the EGR ratio and relative equivalence ratio – lambda. With respect to a catalytic converter installed on the exhaust pipe line, applying EGR appears as better solution for knock reduction then leaning the combustible mixture because the catalytic converter needs stoichiometric mixture for effective NOx reduction. Furthermore, application of the overexpanded cycle to the hydrogen or coke gas fueled IC engine significantly reduces intensity of potential knock by 50 % in comparison to Otto cycle for all loads. Additionally, overexpanded cycle contributes to increase in engine thermal efficiency. Summing up, all the presented measures and technologies can be successfully implemented into practice in stationary engines as well as in traction engines, both of them working on either natural gas or gaseous renewable fuels.