As part of efforts to mitigate climate change by reducing fuel consumption in the transport sector in the Philippines, this paper presents the initial results of an investigation on the effects of engine tuning on fuel economy for different drive cycles using a commercially available piggyback tuning “chip” to modify fuel rail pressure from stock settings of a CRDI diesel passenger van. The drive cycles used in this study were the Japanese 10-15 Mode, US highway fuel economy test (HWFET), and one labeled “SMN” based on a Metro Manila local route. An initial steady state vehicle fuel economy performance map at five speeds per gear position and stock tuning was obtained from chassis dynamometer tests. The same series of tests were done with the tuning chip’s settings of progressively lower rail pressure to identify the setting giving lowest fuel consumption at each gear. Fuel consumption reduction of up to 47% was observed although not all speeds at a given gear and tuning setting gave reduced values. These lowest fuel settings were applied to corresponding gear positions in each of the selected drive cycles resulting to “specific tuning maps” per drive cycle. The test vehicle was then driven with these drive cycle-specific tuning maps and the fuel economy measured. It was found that overall fuel economy decreased with drive cycle-specific tuning settings.

It was then decided to try using a constant tuning setting throughout a drive cycle to see if fuel economy improved. Trials with the Japanese 10-15 Mode cycle at different constant lower rail pressure settings likewise gave overall lower fuel economy. However, a more detailed look showed that in the constant-speed portions of the cycle, fuel consumption savings of up to 35% were realized while it worsened in the accelerating and decelerating sections.

The drive cycle test results indicate that the engine ECU compensated for the lowered rail pressure, maybe with increased injection duration, to increase the amount of fuel injected to meet the road-load requirements imposed by the drive cycle. Control response instabilities may have also contributed to higher fuel consumption. Engine tuning by rail pressure reduction only was most effective in reducing fuel consumption for steady state driving and ineffective for transient driving under the conditions and methodology of this study.

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