Based on the fuel consumption analysis methods published on last year's SETC [1], we compared fuel economies of a typical 125cc production motorcycle equipped with either electronic (port) fuel injection (EFI/PFI) engine management system (EMS) or constant vacuum carburetor (Carb). In addition to earlier discussed PFI results, stationary engine map measurements of fuel consumption on an engine dynamometer (dyno) were conducted for the Carb engine.
The powerful development tool of fuel consumption test cycle simulation uses these stationary engine dyno results to calculate fuel consumption of real transient vehicle operation. Here it was employed to assess economy of both fuel system configurations under different driving conditions. Besides the Indian Driving Cycle (IDC) and the World Motorcycle Test Cycle (WMTC), we investigated real world drive patterns typical for emerging markets in terms of a Bangalore urban cycle and a Malaysian suburban cycle. The results reveal a considerable influence up to 50% of the drive pattern on fuel consumption of both PFI and Carb. We found real urban driving fuel economy to range between soft IDC and demanding WMTC. Comparing fuel systems across the real world drive patterns, the Carb showed 12 to 17% higher fuel consumption than the PFI at colder engine temperature. However, the fuel economy disadvantage diminished for hot engine.
To validate the test cycle simulation results, we conducted transient vehicle measurements of fuel consumption on the chassis dyno, for both vehicle configurations and selected urban drive patterns. These measurements confirmed that a) real world driving takes place at rather cold engine temperatures, and b) fuel economy benefit of PFI relevant for the majority of 2-wheeler end customers is really between 7 and 18%. Thus, the Carb in real world driving is not able to benefit from its theoretical lean combustion thermal efficiency potential.