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Cycle-to-cycle variations in the pressure evolution within the cylinder of a spark ignition engine has long been recognized as a phenomenon of considerable importance. In this work, use of tools borrowed to the nonlinear dynamical system theory to investigate the time evolution of the cylinder pressure is explored. By computing a divergence rate between different pressure cycles versus crank angle, four phases during the combustion cycle are exhibited. These four phases may be identified with the four common phases evidenced by burn rate calculations [1]. Starting from phase portraits and using Poincaré sections, we also study correlations between peak pressures, IMEP and the durations from ignition to appearance of a flame kernel.

The performance of a four-valve engine operating with combustion in all cylinders has been determined in terms of indicated mean-effective pressure, drivability and concentrations of unburned hydrocarbon in the exhaust gases with a stoichiometric mixture of gasoline and air and four injectors including two with air assist. In addition, size and velocity characteristics of the fuel sprays were measured with a phase-Doppler velocimeter outside and inside the engine. With operation at a steady rotational speed of 1200 rpm, the indicated mean- effective cylinder pressure and its covariance were found to be nearly constant with the initiation of injection from 150 to 600 degrees of crank angle after top-dead-centre of intake.

Previous measurements of the velocity, size and number density of droplets have been reported in one cylinder of a production two-valve engine as a function of position, crank angle, injection timing, rotational speed, load and cooling water temperature. In this paper, similar measurements are reported in two cylinders of the same engine, this time with four cylinders firing, and with two manifolds and injectors. They were obtained with a phase-Doppler velocimeter with measurements ensembled in relation to an optical shaft encoder. The engine was also instrumented to provide air and fuel flow rates and temperatures. The results show that most of the droplets emerge in a comparatively small region of the inlet valve and that the characteristics of the spray are important mainly when injection takes place with the inlet valve open.

Fuel intake, start and propagation of combustion were studied in a Z-liter in-line four-cylinder SI engine. Two-dimensional laser induced fluorescence was used to characterize the performance of the engine. A tunable excimer laser at 248 nm and a broadband excimer laser at 308 nm were used to measure simultaneously distributions of hydroxyl radicals and fuel. LIF measurements of fuel (iso-octane) were performed by adding diethyl-ketone as fluorescence tracer to the iso-octane. The complementary information obtained from fuel and hydroxyl radical distributions is shown and differences are pointed out. Cycle to cycle variations and averaged results are discussed as function of equivalence ratio.

A rapid response air-to-fuel ratio sensor manufactured by Nissan has been evaluated for use as a diagnostic tool in engine research. The sensor was calibrated for use with methanol and the time response of the sensor was investigated. Using the sensor's capacity as an extended range oxygen sensor, it was used to monitor the exhaust of a methanol fueled, two-stroke research engine fitted with a prototype air-assisted direct-injection fuel injector. Measurements made at various locations in the exhaust line indicated high levels of short circuited intake air and revealed fluctuations in the measurements due to the sensor's sensitivity to temperature and pressure.