Calculation studies of the influence of exhaust gas recirculation on the characteristics of the natural gas-fueled diesel engine

Abstract

When converting diesel engines to run on natural gas on the gas-diesel cycle, additional problems arise associated with the high thermal stress of the exhaust valves and valve seats at high loads and engine speeds. There is also an increase in NOx emissions due to higher combustion temperatures of natural gas. One of the ways to improve the economic and environmental performance of engines operating on a gas-diesel cycle with a lean air-fuel mixture is to optimize the combustion of the air-fuel mixture by using an exhaust gas recirculation system (EGR). The principle of operation of this system is as follows: exhaust gas entering the intake manifold and further into the combustion chamber reduces the oxygen concentration in the air-fuel mixture, which leads to a dilution effect and, accordingly, to a decrease in combustion temperature and a decrease in NOx content. In order to study the influence of EGR on the dual-fuel gas and diesel engine parameters in the AVL Boost software package, a computer model of the existing 6ChN13/15 engine was developed. A low-pressure EGR system with an exhaust gas cooler was simulated on this engine. Values of NOx emissions, brake specific fuel consumption (BSFC) and brake efficiency have been obtained at different recirculation rate by calculation method. These values allow to estimate the feasibility of using a cooled EGR in a natural gas-fueled diesel engine.