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Abstract



The art of injecting the correct amount of fuel


As my master thesis, I have studied a gaseous sequential injection system (GSI) consisting of a fuel tank, safety shut-off valves, a vaporiser/pressure regulator (V/P), injectors and an electronic control module. The aim of this study was to make a mathematical description of the behaviour of the GSI. The main question has been how to inject the correct amount of fuel. It was important that the developed models could be transformed into real-time running algorithms.

As the GSI injectors were still under development, no study of the injectors has been done. The work has instead been focused on determining the parameters that affect the actual injected amount of fuel, and how to derive them from the parameters measured by the available sensors.

Steady state models describing the pressures and outlet temperature of the vaporiser/pressure regulator, the temperature change of the fuel between the V/P and the injectors, outdoor temperature and tank temperature, have been made. The pressure models have been made by identification, while the models for the outlet fuel temperature of the V/P and the change in temperature before the injectors are based on physical knowledge. The models are all describing the measured data well.

Transient models have been made for the outlet temperature of the V/P and the change in fuel temperature between the V/P and the injectors. When making these models, emphasis was put on making the algorithms easy to calculate in the electronic control module. The transient behaviour has thus been approximated with first order filters and offsets, which gave rather good results.

The developed models can be transformed into real-time running algorithms.

There are some things left to be described, but it seems to be possible to make a real-time running software which calculates how to inject the correct amount of fuel from the information given by the available sensors.

Ylva Nilsson

1999

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