CARE - CAtalytic Reformated Exhaust Gases in Turbocharged DISI-Engines

Today's car manufactures inevitably have to focus on the reduction of fuel consumption while maintaining high performance standards. In this respect, the downsized turbocharged DISI (Direct Injection Spark Ignition) engine represents an appealing solution. However, downsizing is limited because of knocking phenomena occurring at high- and full-load conditions due to autoignition of the unburned mixture ahead the flame front. A common way of reducing knock tendencies is provided by Exhaust Gas Recirculation (EGR). However, EGR modifies the chemical composition of the cylinder charge and recirculated species like nitric oxide (NO) or unburned Hydrocarbons (HC) particularly increase the reactivity of the unburned mixture. In other words, the EGR influences the Octane Number (ON) of the in-cylinder gases. This paper proposes a new EGR concept in which a catalytic converter is introduced into the EGR system in order to minimize the NO and HC concentrations and thereby to reduce the reactivity of EGR. Pressure trace and infrared-spectral measurements are carried out on an engine test bed including a standard three-way-catalyst in the high- pressure EGR pipe of a turbocharged DISI engine. Pressure trace measurements allow thermodynamic analysis, while IR-spectral analysis identifies the concentrations of EGR species in the EGR pipe. Furthermore, a zero-dimensional reactor-network modeling the EGR pipe and the combustion chamber is used to numerically investigate the influence of EGR species on the autoignition processes. Both experimental and numerical results show a potential benefit introduced by catalytic reformation of exhaust gases for turbocharged DISI engines in terms of reduced fuel consumption.