The effects of carbon dioxide in exhaust gas recirculation on diesel engine emissions

Abstract

The investigation was conducted on a high-speed direct injection diesel engine and was concerned with the effects of exhaust gas recirculation (EGR) on diesel engine combustion and emissions. In particular, the effects of carbon dioxide (CO2), a principal constituent of EGR, on combustion and emissions were analysed and quantified experimentally. The use of CO2 to displace oxygen (O2) in the inlet air resulted in: reduction in the O2 supplied to the engine (dilution effect), increased inlet charge thermal capacity (thermal effect), and, potentially, participation of the CO2 in the combustion process (chemical effect). In a separate series of tests the temperature of the engine inlet charge was raised gradually in order to simulate the effect of mixing hot EGR with engine inlet air. Finally, tests were carried out during which the CO2 added to the engine air flow increased the charge mass flowrate to the engine, rather than displacing some of the O2 in the inlet air. It was found that when CO2 displaced O2 in the inlet charge, both the chemical and thermal effects on exhaust emissions were small. However, the dilution effect was substantial, and resulted in very large reductions in exhaust oxides of nitrogen (NO x) at the expense of higher particulate and unburned hydrocarbon (uHC) emissions. Higher inlet charge temperature increased exhaust NO x and particulate emissions, but reduced uHC emissions. Finally, when CO2 was additional to the inlet air charge (rather than displacing O2), large reductions in NOx were recorded with little increase in particulate emissions.

Effects of Buffer Gas Composition on Autoignition of Dimethyl Ether

“…In the work by Ladommatos et al [1], the authors separately studied the thermal, chemical and dilution effects of EGR on the ignition delay on a high-speed direct injection diesel engine. The authors found that the dilution effects have the largest impact on the ignition delay and exhaust gas emissions.…”

Control of NOx from A DI Diesel Engine With Hot EGR And Ethanol Fumigation: An Experimental Investigation

“…EGR involves routing a fraction of engine exhaust gas into the intake manifold where it mixes with the incoming fresh air before being taken in to cylinder [4][5][6]. Peak combustion temperatures are one of the main factors for the formation of NOx and it can be greatly suppressed when the O 2 concentration in the combustion chamber is reduced.…”

“…It is a result of condensation of hydrocarbon. Presence of soot is mostly through incomplete combustion of fuel, condensation of hydrocarbons due to decreased combustion temperatures with small contributions from the lubricating oil [32]. More difficult pulverisation of the heavy fuel droplets and non-homogeneous mixing leads to incomplete combustion resulting into emission of smoke and HC.…”

The Effects of EGR on the Performance and Exhaust Emissions of a Diesel Engine Operated on Diesel Oil and Soybean Oil Methyl Ester (SOME)

“…They noticed a large reduction in NOx emissions at the expense of higher particulate and un-burnt hydrocarbon emissions. [1]. D. Agarwal (2006) suggested that controlling the NOx emissions primarily requires reduction of in-cylinder temperatures.…”