The Dilution, Chemical, and Thermal Effects of Exhaust Gas Recirculation on Disesel Engine Emissions - Part 4: Effects of Carbon Dioxide and Water Vapour

An investigation was conducted with the aim of identifying and quantifying the effects of exhaust gas recirculation (EGR) on diesel engine combustion and exhaust emissions. Five effects of EGR were identified and investigated experimentally: the reduction in oxygen supply to the engine, participation in the combustion process of carbon dioxide and water vapour present in the EGR, increase in the specific heat capacity of the engine inlet charge, increased inlet charge temperature and reduction in the inlet charge mass flowrate arising from the use of hot EGR. The experimental methodology developed allowed each one of these effects to be investigated and quantified separately. The investigation was carried out on a high-speed, direct injection diesel engine, running at an intermediate speed and load. A limited number of tests were also conducted in an optically accessible diesel engine, which established the effects of EGR on local flame temperature. Finally, tests were conducted with simulated EGR being used additionally to the engine air supply. This contrasts with the conventional use of EGR, whereby EGR replaces some of the air supplied to the engine. It was found that the first effect of EGR (reduction in the oxygen flowrate to the engine) was substantial and resulted in very large reductions in exhaust NOx at the expense of higher particulate emissions. The second and third effects (participation of carbon dioxide and water vapour in the combustion process and increase in the charge specific heat capacity) were almost insignificant. The fourth effect (higher inlet charge temperature) increased both exhaust NOx and particulate emissions. The fifth effect (reduction in the inlet charge due to thermal throttling) reduced NOx but raised particulate emission. Finally, when EGR was used additionally to the inlet air charge (rather than displacing air), substantial reductions in NOx were recorded with little increase in particulate emission.

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

Proceedings of the Institution of Mechanical Engineers Part D Journal of Automobile Engineering ◽

10.1243/0954407981525777 ◽

1998 ◽

Vol 212 (1) ◽

pp. 25-42 ◽

Cited By ~ 73

Author(s):

N Ladommatos ◽

S M Adelhalim ◽

H Zhao ◽

Z Hu

Keyword(s):

Carbon Dioxide ◽

Diesel Engine ◽

High Speed ◽

Combustion Process ◽

Dilution Effect ◽

Exhaust Gas Recirculation ◽

Chemical Effect ◽

Particulate Emissions ◽

Exhaust Gas ◽

Gas Recirculation

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.

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The Effects of Exhaust Gas Recirculation and Residual Gas on Engine Emissions and Fuel Economy

10.4271/750414 ◽

1975 ◽

Cited By ~ 6

Author(s):

Yasuo Kaneko ◽

Hiroyuki Kobayashi ◽

Reijiro Komagome

Keyword(s):

Fuel Economy ◽

Exhaust Gas Recirculation ◽

Exhaust Gas ◽

Engine Emissions ◽

Residual Gas ◽

Gas Recirculation

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