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Technical Paper

A Comprehensive Study of Wankel Engine Performance

An extensive experimental and analytical study of the performance of a Wankel engine is reported, with special emphasis on the combustion process. A one dimensional technique for calculating gas velocities in the combustion chamber under motoring conditions is described and this is then used to evaluate flame travel when combustion occurs. A novel three-zone combustion model is introduced. The effect of the position of the rotor recess is examined and shown to change the engine power output and hydrocarbon emissions.
Technical Paper

A Free-Piston Engine Hydraulic Pump for an Automotive Propulsion System

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.
Technical Paper

A Generalized Computer Aided Design Package for I. C. Engine Manifold System

A numerical scheme for a Computer Aided Design (CAD) package for the design and development of internal combustion engine intake and exhaust manifold is presented. The program is interactive and uses the graphical and visual display unit (VDU) facilities extensively. The basic concept of such a program was described in a previous SAE paper (Paper No. 790277) by one of the authors (SCL). The present program is written to handle a maximum of 10 cylinders and any imaginable configuration of intake and exhaust manifold. The input data, the preparation of which is usually a time-consuming process, are kept at a possible minimum with automatic generation of data from arbitrary drawings drawn manually on the VDU screen. The program is applied to a commercial 4 cylinder - 4 stroke spark ignition engine.
Technical Paper

A Simulation Model for Transient Operation of Spark-Ignition Engines

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.
Technical Paper

An Experimental and Theoretical Investigation of a Twin-Entry Radial Flow Turbine under Non-Steady Flow Conditions

One of the methods of representing a turbocharger-turbine in the exhaust system of internal combustion engines is by assuming quasi-steady flow at turbine boundaries, while taking into account the generation of pressure waves both upstream and downstream of the turbine due to non-steady flow conditions. This method relies substantially on steady flow turbine characteristics for the generation of boundary conditions. A method is presented to allow for wave action both upstream and downstream of a twin-entry radial inflow turbine. The method also allows for different flow rates in each entry to simulate the partial admission condition. Comparison is made between experimental results and theoretical analysis.
Technical Paper

Performance and Emission Predictions for a Multi-Cylinder Spark Ignition Engine with Catalytic Converter

A mathematical model is developed to represent an oxidizing catalytic converter in the exhaust system of a spark ignition engine in which the flow is non steady. By using the basic mass transfer, heat transfer and chemical reaction rate equations on the path lines the heat generated at the catalyst surface and the friction factor are allowed for in the generalized non steady flow relations using the method of characteristics. The model is included in a multi-cylinder engine simulation program. Secondary air injection into the exhaust system is represented by a simple mixing process without chemical reaction. A series of tests were carried out on a four cylinder two litre engine with a carbon monoxide and hydrocarbon oxidizing converter and secondary air injection. Comparison of results between experiments and computer calculations shows excellent agreement when the converter is new, but that if the catalyst surface is poisoned or aged the hydrocarbon prediction deteriorates.
Technical Paper

Performance and Emission Predictions of a Multi-Cylinder Spark Ignition Engine with Exhaust Gas Recirculation

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.
Technical Paper

Some Further Tests on a Computer Program to Simulate Internal Combustion Engines

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.
Technical Paper

Transportation of Liquid Fuel Droplets in the Pulsative Air Flow Within the S.I. Engine Intake Manifold

An extensive amount of research has been carried out by various authors on the entrainment of fuel droplets in a steady air flow, in order to understand the transportation of droplet fuel in the spark-ignition engine intake manifold system. However, the utility of this type of steady state model is very limited when applied to the real engine where the air flow is highly pulsative. The present work develops a theoretical model of the flow of fuel droplets entrained in a non-steady air flow which requires the solution of a set of unsteady one-dimensional two phase flow equations by a numerical technique. This model is then applied to a single-cylinder spark-ignition engine fitted with both intake and exhaust manifold systems and also a carburettor.