A Comparison of Gasoline Direct Injection Part I - Fuel System Deposits and Vehicle Performance

Four 1998 Mitsubishi Carismas, two equipped with direct injection and two with port fuel injection engines, were tested in 20,100 km intervals to determine the effect of mileage accumulation cycle, engine type, fuel and lubricant on vehicle deposits and emissions, acceleration and driveability performance. The program showed that engine fuel system deposits, including specifically those on intake valves, combustion chambers and injectors are formed in higher amounts in the GDI engine than the PFI engine. The fuel additive used reduced injector deposits and combustion chamber deposits in the GDI, but had no significant effect on intake valve deposits, which are affected by crankcase oil formulation. In GDI vehicles, deposited engines were found to have increased hydrocarbon and carbon monoxide emissions and poorer fuel economy and acceleration, but lower particulate emissions. Effects in PFI engines were directionally the same for NOx and particulates but the opposite for HC and CO emissions and fuel economy. In terms of specific deposit effects in the GDI engine, CCD is correlated with poorer acceleration, HC and CO emissions, while injector deposits correlate with NOX formation.