Laser induced fluorescence for the measurement of air-to-fuel ratios in gasoline direct injection engines
In view of current and future legislation, gasoline direct injection engines have been
developed as a means of lowering fuel consumption and pollutant emission. These objectives
are achieved through the use of a `lean-burn' technique, where the fuel concentration inside
the cylinder is significantly lower than stoichiometric. This low fuel concentration is
compensated by a stratification process where the fuel is concentrated around the spark plug,
so that ignition is still possible. In order to advance the development of gasoline direct
injection engines, it is important to understand the fuel distribution process itself.
Standard fuel concentration measurement techniques such as exhaust valve sampling or
catalytic hot wire probes can only provide time- and space-averaged data. On the other hand
optical laser techniques can provide the same information with a much greater spatial and
temporal resolution. Among these techniques Laser-induced fluorescence (LIF) allows the
measurement of 2-dimensional molecules distribution and is traditionally used to measure in cylinder
fuel concentration qualitatively.
The LIF signal is directly proportional to the concentration of the fluorescing tracer. However
it is also dependent on pressure, temperature and surrounding species, parameters which are
difficult to quantify in an engine. Consequently most LIF measurement can only be performed
qualitatively. Performing quantitative measurements is however a much tougher challenge.
The main objective of this thesis is to present the development of a new technique for the
calibration of LIF measurement of fuel concentration in the cylinder of a direct injection
engine and to apply this method for gaining an understanding of the air and fuel mixing