Simultaneous Quantitative Measurements of Temperature and Residual Gas Fields Inside a Fired SI-Engine Using Acetone Laser-Induced Fluorescence

In most optimization strategies of combustion processes in gasoline IC engines, spatial inhomogeneities of the temperature, of the residual exhaust gas and of the fuel-air distribution play a major role. Hence, the development of experimental methods for the simultaneous quantification of both, concentration and temperature fields, is highly desirable. One method which is in particular suitable for measuring these quantities is the technique of two-laser excitation of the fluorescence of ketones like 3-pentanone and acetone. Different groups have used 3-pentanone for the measurement of fuel concentration. In this work we present the determination of the exhaust gas concentration field simultaneously with the temperature field using acetone as an intake air tracer. Acetone is a more suitable gas tracer than 3-pentanone due to its higher vapor pressure and its better stability regarding thermal decomposition.

In the first part of this work results from the calibration of the fluorescence behavior of acetone are presented. Relative signal intensities for the excitation wavelengths 248 nm and 308 nm are given with respect to standard conditions of 295 K and 0.1 MPa. Also the directly measured intensity ratio of both wavelengths for temperature measurements is given. The results are presented for two bath gases, air and a synthetic exhaust-gas-air-mixture. Temperatures and pressures are varied simultaneously in the range from 295 K to 728 K and 0.05 MPa to 2 MPa, respectively. In the second part, two-dimensional in-cylinder measurements of temperature and exhaust gas fraction are presented for the intake and compression stroke in a fired SI-engine with optical access. The temperature measurements during compression stroke match very well a polytropic approximation. Simultaneously acquired temperature and exhaust gas fields during intake stroke are presented. Additional information is given on the achievable accuracy and precision of these in-cylinder measurements.