a b s t r a c t
This study was conducted to investigate the combustion and emissions characteristics of the
first-combustion cylinder in a direct-start process. The explosive energy of the first combustion is important
for the success of a direct start, but this combustion was rarely addressed in recent research. For a
2.0 L direct-injection spark-ignition engine, the in-cylinder mixture concentration, cylinder pressure,
engine speed and exhaust hydrocarbon concentration were detected to analyze the fuel evaporation,
combustion, engine movement and engine emissions, respectively. In the first-combustion cylinder of
the direct-start process, the injected fuel was often enriched to ensure that an appropriate mixture concentration
was obtained for ignition without misfiring. Approximately one-third of the injected fuel
would not participate in the combustion process and would therefore reduce the exhaust hydrocarbon
emissions. The start position determined the amount of the total explosive energy in the
first-combustion cylinder, and an optimal start position for a direct start was found to be at a 70–80!
crank angle before the top dead center to obtain a better combustion performance and lower emissions.
A lower coolant temperature increased the maximum explosion energy of the first combustion, but additional
hydrocarbon emissions were generated. Because there was almost no problem in the direct-start
capability with different coolant temperatures after an idling stop, it was necessary to maintain the coolant
temperature when the engine was stopped.