Residual gas fraction in an engine cylinder affects engine performance, efficiency and emission characteristics. With high residual gas fractions, flame speed and maximum combustion temperature are decreased and these are deeply related with combustion stability especially at idle condition and NOx emission at relatively high engine load.
In this work, the residual gas fraction was measured in an heavy duty LPG liquid injection engine under various rpm and torque conditions. GC(Gas Chromatography) was used for measurement of $CO_2$ concentration and high speed solenoid valve was used for sampling of $CO_2$ in the cylinder.
Residual gas fraction was increased as engine speed and torque were decreased. Those phenomena were related with back flow which was generated by difference between intake and exhaust pressure during valve overlap time.
In exhaust gases, THC was decreased with high rpm and high torque while NOx, CO2 and exhaust gas temperature were increased.
A comparison between experimental and computational calculation results was made and also compared with a commercial 1-D calculation, which was called WAVE. Both computational calculation and WAVE showed same tendency with experimental result, with some discrepancies.
