Exhaust gas recirculation (EGR) is a common state of the art technology to reduce NOx emissions in internal combustion engines. Owing to the exponential dependency of NOx formation on temperature, the effect of EGR is to increase combustion duration and thus, to reduce the peak temperature in the combustion chamber. The variation of EGR rates has effects on the combustion process and NOx formation. Furthermore, according to the setup of the EGR system, the EGR supplied interferes with the air dynamics at the intake manifold affecting the delivery ratio, especially in a naturally aspirated combustion engine. Depending on the setup of the EGR line, it is possible to condense out a major amount of water, which effects the caloric mixture properties.

Hence, the scope of this paper is to identify the difference between two types of EGR setups by using a modified single cylinder gas engine fed with hydrogen. In this investigation, emissions and performance parameters are measured and compared for a wet EGR setup and a dry EGR setup. Using dried EGR the NOx emissions decrease with the increase of the EGR rate. The exhaust gas temperature and the efficiency are nearly constant with the increase of EGR rate. Using wet EGR the NOx emissions increase at low EGR rates and decrease at high EGR rates.

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