Cold Start Diagnostics Of PFI Gasoline Engines

Vehicle cold-start problems often occur in winter.Many vehicles can’t start successfully before moved to distributor from assembly plant,especially in north cold area in China.In this paper,the cold start failure mechanism and its main impact factors are researched.First,the failure information including vehicle mileage,failure time,failure area,solutions are analyzed systematically.The results obviously show that,most of the cold-start problems occur before mileage reaching 20 km,especially in north cold winter.The main failure reason is spark plug fouling and most of the cold-start problems can be solved by changing spark plug,which is fail to initial a strong enough flame kernel to start engine because of fouling.A quick and repeatable test procedure called Three Pulses Test(TPT)has been developed to investigate cold-start spark plug fouling according to the cold-start failure work condition.Second,CFD simulation is conducted to investigate the spark plug fouling mechanism.The results show that the droplets produced by injectors may crash on the center-electrode of spark plug and form liquid film after intake valves open,and the distribution of liquid film is the same as carbon deposited on the top of spark plug.Therefore,author guesses that liquid film may be the main reason of spark plug fouling.CFD simulation also shows that optimizing spray targeting and shortening center-electrode of spark plug can reduce the quantity of liquid film crashed on the top of spark plug.Finally,the TPT is carried out to validate CFD simulation results.The results show that reducing liquid film is effective to suppress spark plug fouling.Injection calibration has strong influence on spark plug fouling.Spark plug core nose coated with silicone and gasoline additive 9522 C can also suppress spark plug fouling.