Abstract
Combustion with significantly low Emission matter (EM) and excellent thermal efficiency was achieved by means of a large amount of Exhaust Gas Recirculation (EGR) and excessive cooled intake gas. Engine test was conducted on the 2.0 litres 4-cylinders engine at 1500rpm-20% load in order to select the optimum combustion conditions (how much EGR amount and how much cooled intake gas.) The results indicated that the optimum combustion enables to reduce both NOx and Smoke significantly with restraining CO, HC, and combustion noise, while ignition timing near to TDC is under the control and fuel economy is excellent.
The findings about the optimum combustion mechanism, with analyzed Computational fluid dynamics (CFD) -T distributions, can be summarized as follows:
- A large amount of EGR effectively reduced NOx by lowering combustion temperature.
- Excessive cooled intake gas, in addition to the EGR, effectively reduced Smoke, because the moderate ignition delay (the ignition occurs after the end of injection, so-called "PCCI") and high over all (sufficient excess oxygen) enable to cope with both the restraint of Soot generation and the acceleration of Soot oxidation.
- The combination of excessive cooled intake gas and large amounts of EGR also restrained CO and HC since the mixture became leaner and the local combustion temperature did not drop too much in the latter combustion period (due to PCCI and high .)
The application of this low EM mechanism was further expanded by adding methods that accelerate mixing without lowering (e.g., compression ratio reduction and multiple injections) to an upper limit of 2000rpm-40%load.
Keywords:Diesel engine, Combustion, Computational fluid dynamics, EGR, Intake gas temperature, NOx, Soot, Fuel consumption