Study on the Ignition, Combustion and Emissions of HCCI Combustion Engines Fueled With Primary Reference Fuels 2005-01-0155
This article investigates the basic combustion parameters including start of ignition, combustion duration, and CO, UHC, and NOx emissions of HCCI combustion engines fueled with primary reference fuels and their mixtures. A single-cylinder HCCI combustion engine, which was converted from a four-cylinder high-speed diesel engine, was used to the tests. Two primary reference fuels, n-heptane and iso-octane, and their mixtures including RON25, RON50, RON75, and RON90 were evaluated. In addition, the effects of cooled EGR on the HCCI combustion and emissions were also studied.
The experimental results shown that, in the first-stage combustion, with the increase of the research octane number, the start of ignition retards, the combustion duration shortens, and the pressure rising and the temperature rising during the first-stage combustion decrease. Furthermore, the cumulative heat release in the first stage is strongly dependent on the concentration of n-heptane in the mixtures. The start of ignition of the second-stage combustion is linear with the start of the ignition of the fist stage. The combustion duration of the second stage decreases with the increase of the equivalence ratio and the decrease of the research octane number.
The EGR tests indicated that the combustion phasing of the first-stage and second-stage combustion retard, and the combustion duration prolongs with the introduction of cooled EGR. At the same time, a higher EGR rate can be tolerated for the HCCI combustion using a high cetane number fuels, such as n-heptane and RON25, but only 45% EGR rate for RON75 at 1800r/min. Furthermore, there is a moderate effect of EGR rate on CO and UHC emissions for HCCI engines fueled with n-heptane and RON25, but a distinct effect on emissions for higher octane number fuels