A study of in-cylinder fuel–air mixing distributions in a firing gasoline-direct-injection engine is reported using planar laser-induced fluorescence (PLIF) imaging. A multi-component fuel synthesised from three pairs of components chosen to simulate light, medium and heavy fractions was seeded with one of three tracers, each chosen to co-evaporate with and thus follow one of the fractions, in order to account for differential volatility of such components in typical gasoline fuels. In order to make quantitative measurements of fuel–air ratio from PLIF images, initial calibration was by recording PLIF images of homogeneous fuel–air mixtures under similar conditions of in-cylinder temperature and pressure using a re-circulation loop and a motored engine. This calibration method was found to be affected by two significant factors. Firstly, calibration was affected by variation of signal collection efficiency arising from build-up of absorbing deposits on the windows during firing cycles, which are not present under motored conditions. Secondly, the effects of residual exhaust gas present in the firing engine were not accounted for using a calibration loop with a motored engine.

A two-dimensional finite element model has been used to analyze the unsteady heat conduction behavior of an eroding type of surface thermocouple. The impulse response of the thermocouple was analyzed by using both a one-dimensional solution and a two-dimensional model. The experimental impulse response of the thermocouple was investigated by a laser impulse excitation experiment to validate the modelling results. The modelling results showed that there was a significant difference between the two-dimensional modelling and the one-dimensional analytical solution, especially before 1 ms. The two-dimensional modelling result is closer to the laser impulse experiment result, which implies the existence of a multi-dimensional effect on the transient heat conduction within the eroding thermocouple. Engine heat flux measurements were obtained using the impulse response analysis, and a comparison of the computed heat flux has been made using the experimental impulse response and the different models. The use of a laser impulse calibration is recommended. If a model is to be used then it should be a 2-D model, but if only a 1-D model is available, then the 1-D model should be based on the properties of the alumel.

Color-ratio pyrometry (CRP) is a technique for estimating the temperature and loading of soot, based on its thermal emission spectrum. This technique is contrasted with conventional two-color pyrometry which requires absolute measurements of the radiation intensity, either at two specific wavelengths or ranges of wavelengths. CRP uses two ratios, obtained by measuring the radiation intensity for three wavelengths or wavelength bands. CRP has been implemented here by using a digital CCD camera, and full details of the calibration are reported. Because of uncertainties in the emissivity of reference sources (such as tungsten ribbon lamps, in which the emissivity depends on temperature and wavelength), then a spectroscopic calibration of the CCD camera has been used. Use of a CCD camera is not straightforward because of internal digital signal processing (DSP), so full details are given of the calibration and technique implementation. Calibration results, together with an error analysis, showed an accuracy of ±50K within the combustion temperature range and a preference for the temperature estimates based on the red/green ratio over the red/blue ratio at low temperatures and the red/blue ratio over the red/green ratio at high temperatures. Temperature estimates are shown to be insensitive to the concentration of soot. Combustion imaging was later carried out on a sprayguided direction injection spark ignition engine with optical access. Temperature estimates under various imaging timings and mixture strengths are presented. With a fixed operating point the maximum in-cylinder temperature occurred just after top center, and this coincided with the maximum rate of heat release. When the mixture strength was varied, the maximum temperature (at a particular crank angle) was rich of stoichiometric. Finally, temperature and KL results using the variable KL algorithm were reported together with discussions about soot formation.