Search Results

A generalized computer model for analysis of multicylinder spark-ignition engines under transient conditions is presented. The model utilizes a two-zone combustion submodel based on flame propagation. It accounts for heat transfer and uses a chemical-kinetics-based procedure for the prediction of nitric oxide and carbon monoxide concentrations. Non-linear wave interactions in the exhaust and intake manifolds are considered. For the transient analysis, a vehicle model is coupled to the engine via a geartrain. The model was used to predict the behavior of two four-cylinder engines under a variety of transient operating conditions. The simulation enabled systematic analysis of the interaction between various dynamic, thermodynamic, and emission variables under transient operating conditions of the engines.

A free-piston engine hydraulic pump (FPEHP) is considered as a power source in the propulsion system of an automotive vehicle. The propulsion system uses a two-stroke spark-ignited free-piston engine coupled to a hydraulic pump and an accumulator where high pressure hydraulic fluid is stored for transmission of power. The energy in the accumulator is transmitted to hydraulic motors which provide the tractive effort. A mathematical model was developed for the FPEHP and computer simulation studies were performed. A particular free-piston engine hydraulic pump concept was simulated at various operating conditions and compared with a similarly-sized conventional engine. We can conclude that the FPEHP engine has no thermodynamic advantage over a conventional engine, but there are reduced nitric oxide emissions. Also, the FPEHP has a limited range of engine speed and a narrower range of ignition timing than a conventional engine.

A multi-cylinder four stroke cycle spark ignition engine equipped with an exhaust gas recirculation (EGR) system to reduce nitric oxide emission has been comprehensively simulated in a computer program including intake and exhaust manifolds. The program was tested against experiments performed on a standard production four cylinder four stroke engine equipped with a simple laboratory made EGR system. A nitric oxide emission reduction of about 50% was obtained at the peak NO condition. In spite of simplified assumptions the comparison between prediction and measurement of some major engine variables was good. The simulation program holds promise as a tool for engine development work. An appendix is added giving the outline of the calculation procedure.

Comparison is made between the transient response of a medium-speed, turbocharged diesel engine subjected to sudden load changes on a test bed and the response of a computer simulation model of the engine. Brief details are given of the simulation techniques involved and the data required to set up the model. Despite close agreement of model and engine steady-state results over the whole normal operating range, the transient responses of the model were initially found to be much faster than the test-bed responses. It is shown that the most important factor causing this difference is the lack of knowledge of the combustion at low air-fuel ratios and hence prediction of engine exhaust temperature during transient operation. Good agreement was obtained when this was modified.

The results are presented of an extensive series of tests on a turbocharged 4-stroke diesel engine in which the test results are compared with predictions using a generalized computer program. An examination is made of the influence of the cylinder heat transfer coefficient, the cylinder wall temperature, the exhaust pipe wall temperature, and the air valve flow areas on the engine and turbocharger performance predictions in order to establish the limits of accuracy required for these data. The effect of including the intake system in the calculation is also examined. Results are presented comparing the actual performance of the turbocharger with the predicted performance using steady flow data.

A simulation model of a turbocharged diesel engine has been set up on an analog computer for studying the performance under transient load conditions. The method uses simplified compressor and turbine characteristics and empirical relationships for the engine thermodynamics. Steady-state results and transient responses for various load changes are compared with corresponding results from a similar digital model and with test-bed results where available. Proposed improvements to the analog model include the transfer of the compressor and turbine characteristics to the digital section of a hybrid computer which will allow a considerably better representation of the turbocharger to be obtained.