An experiment has been carried out to investigate the combustion
process in an operating S.I. engine (MPI and Multi- valve), using
in-cylinder high speed gas sampling techniques.
Measurements have been made of local air fuel ratios and
time-resolved concentrations of combustion gases such as CO, CO2,
THC, NOx, and O2, particularly focused on spark plug location. The
effects of fuel injection timing, swirl generating air motion,
sampling location, spark timing, speed and load have been
considered.
With the end of fuel injection at 120° ATDC on the intake
stroke, A/F ratio at spark plug location has the leanest value for
standard inlet port, while it has the richest value for swirl
generating inlet port. The initial NOx concentration in the
unburned gas region, diluted by the residual gases, has been
substantially reduced between 5° BTDC and 15° ATDC crank angle
prior to combustion. It has also been found that in- cylinder high
speed gas sampling method is a useful tool to investigate the
combustion phenomena in an operating S.I. engine.