Experimental investigation on the time resolved THC emission characteristics of liquid phase LPG injection (LPLi) engine during cold start

This work investigates the total hydrocarbon (THC) emission characteristics in a liquid phase LPG injection (LPLi) engines during cold start operation. To clarify the THC formation mechanism of the LPLi engines, the effect of various spark timings during cold start was investigated using a fast response THC analyzer and combustion analyzer. A cycle-to-cycle combustion analysis showed that the majority of THC emissions are emitted within the first few seconds after engine start. The emission results for vehicle test indicated that exhausted THC during phase 1 of FTP-75 mode decreased by 23% at top dead center (TDC) spark timing and by 31% at after top dead center (ATDC) 10° crank angle (CA) compared to that with a conventional spark timing of before top dead center 10° CA. In addition, catalyst light off times were shortened by 7 and 10 s in case of TDC and ATDC 10° CA spark timings, respectively. Consequently, it was founded that the control strategy of retarding spark timing during cold start in the LPLi vehicle was a very effective method to reduce THC emissions.