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Previous papers from The Queen's University of Belfast have described a new non-isentropic branched pipe junction model for use in a one-dimensional gas dynamic simulation of a multi-pipe system subject to unsteady gas flow. Such assemblages are commonly found in the intake and exhaust systems of multi-cylinder engines. The model takes full account of the effect of pressure loss, due to change in flow direction, and tracks the properties and composition of gas mixtures through the junction. Although the validity of the model has previously been inferred by its use in a complete engine simulation, which accurately predicted parameter variation in a firing engine, the independent validation of the junction model by itself is only now demonstrated. To investigate the performance of the junction model a series of three-pipe junctions were tested by directing a single pressure wave through each of the previously quiescent junctions.

The improvement of computer simulation packages with experimentally validated sub-models has benefited the engine designer in reducing development time and costs. Such packages offer invaluable information regarding the internal gas dynamics and gas exchange characteristics. Presented are measured dynamometer results of a RS Honda 125 cm3 two-stroke single-cylinder motorcycle grand prix road-racing engine operating at full throttle from 9000 rev/min to 13000 rev/min. The engine is instrumented to provide in-cylinder and exhaust pipe pressure crank-angle histories. All relevant engine geometry, discharge coefficients, scavenging characteristics and combustion data are used to simulate the engine using a one-dimensional (1-D) engine simulation package. In-cycle crankshaft angular velocity fluctuations are also considered. Performance parameters such as power, BMEP and delivery ratio, together with pressure diagrams are compared to the measured data.

Previously, an initial investigation examined the effect of the catalytic substrate on the gas dynamics of the blowdown pulse on the QUB single shot rig. This initial investigation measured the resulting waves from the catalytic converter in the exhaust pipe. In this early study the substrate was at ambient temperature but it is recognised that after light-off higher reaction temperatures will result from the exothermic nature of exhaust gas oxidation and reduction. Therefore substantially different results will occur. This paper details a series of experiments which investigate the influence of an operating catalyst on the unsteady gas dynamics in an exhaust system using the QUB single shot rig. In addition to measuring the effect of temperature on the gas dynamics previous work is reviewed with emphasis now on specifically measuring the features present rather than having to decipher superimposed pressure traces.

The gas exchange process of the two-stroke engine is such that the flow of fresh air into the cylinder and exhaust gas out of the cylinder occur substantially together. It is therefore the case that not all of the air delivered will be trapped during this scavenge process. Extensive research has already been conducted into optimising the porting layouts of two-stroke engine cylinders. One of the techniques developed at The Queen's University of Belfast for evaluating scavenging is a unique experimental method described as the ‘single cycle scavenge test’. Although the test does not reflect the actual scavenge process in a firing engine, it is a sufficiently useful procedure to have become an industrial standard for scavenge evaluation. This paper discusses the application of that test procedure in the development of a multicylinder, externally scavenged, two-stroke automotive engine.

The performance characteristics of two-stroke engines are highly dependent upon the gas dynamic wave action in the exhaust system. In a tuned high performance exhaust system, negative suction pulses aid induction of charge into the cylinder, while positive waves aid its retention. The timing of these waves is closely related to the acoustic velocity, and is therefore dependent on the exhaust gas temperature (EGT). In advanced engine management systems, the control strategy may be tailored to influence the EGT, and to maximize the beneficial influence of the gas dynamics in the exhaust. Therefore, accurate measurement of EGT is required for development purposes, and real-time feedback could potentially be used as an input to the management system. However, accurate measurement of exhaust gas temperature is fraught with difficulties due to a number of sources of error.

Presented is a study that expands the body of knowledge on the effect of in-cycle speed fluctuations on performance of small engines. It uses the methods developed previously by Callahan, et al. (1) to examine a variety of two-stroke engines and one four-stroke engine. The two-stroke engines were: a high performance single-cylinder, a low performance single-cylinder, a high performance multi-cylinder, and a medium performance multi-cylinder. The four-stroke engine was a high performance single-cylinder unit. Each engine was modeled in Virtual Engines, which is a fully detailed one-dimensional thermodynamic engine simulator. Measured or predicted in-cycle speed data were input into the engine models. Predicted performance changes due to drivetrain effects are shown in each case, and conclusions are drawn from those results.

This paper describes the preliminary stages in the design of a low emission, multi-cylinder two-stroke engine for application in a luxury passenger car. A crankshaft driven compressor is used to provide scavenge air, exhaust timing edge valves are specified and also a valve able to disable transfer ports. Fuelling is provided by injection directly into the cylinder head. Rationale is given for the choice of the engine configuration, the scavenge system used and the definition of key features. A parametric investigation, performed by gas dynamic simulation, is presented illustrating the influence on the engine of: compressor speed ratio, exhaust manifold branch lengths, exhaust pipe lengths, and transfer and exhaust port timings. Finally, details are given of the design of the cylinder block, the exhaust valve and the intake valve.

Coefficient of discharge for a particular flow discontinuity is defined as the ratio of actual discharge to ideal discharge. In an engine environment, ideal discharge considers an ideal gas and the process to be free from friction, surface tension, etc. Discharge coefficients are widely used to monitor the flow efficiency through various engine components and are quite useful in improving the performance of these components. In modelling the flow through internal combustion engines it is equally important to have accurate values for coefficients of discharge through the combinations of valves, ports and ducts. It is especially important when modelling high performance two-stroke engines, due to the relatively high flow rates and the rapidly changing flow directions. Such an engine relies on the plugging pulse from the tuned exhaust system to ram escaped fresh charge back into the cylinder, prior to exhaust port closure.

This paper details an investigation of the output performance of an externally scavenged, single cylinder, two-stroke cycle engine. The engine was of the loop scavenged type with scavenge air supplied by a crankshaft driven supercharger. The main emphasis was to investigate the effects of exhaust and transfer port timings and also to evaluate the effectiveness of different supercharger drive ratios. The engine was run using two different fuel systems; one being a high pressure liquid system injecting directly into the cylinder head and the other being a low pressure liquid system injecting into the intake system. Provision was provided for four different timing edges for both exhaust and transfer ports. In each configuration the engine was performance tested over a range of operating conditions while the fuel efficiency, brake specific emissions and air flow characteristics were recorded.

A single-cylinder, 500cc research engine was tested under Spark-Ignition (SI) and Controlled Auto-Ignition (CAI) operation with similar load and speed conditions. Camshafts with low-lift and short duration, run with a negative valve overlap, were used to obtain CAI at wide open throttle. Two different camshaft profiles were tested in order to get a wide span of loads at 1200 and 2000rpm. The SI engine was Port Fuel-Injected (PFI) while the CAI engine was tested with both PFI and an Orbital Air-Assist Direct-Injection (DI) system. To reduce the high Indicated Specific Nitrogen Oxide (ISNOx) emissions at λ=1, 10% External Exhaust Gas Residuals (EEGR) was applied to the SI engine. EEGR reduced ISNOx emissions and there was slight reduction in ISFC. However, when the engine was tested in CAI mode, both ISNOx and ISFC were lower than the SI engine.

The performance of two-stroke, high specific output engines, is largely dependent on the exhaust system. This paper describes an experimental study on the effect of each of the exhaust pipe sections on the actual engine performance. The exhaust system has been designed with interconnecting flanges that allow the various sections to be bolted together for testing on a dynamometer. This allows numerous combinations of various section designs to be evaluated. In an effort to understand the exact mechanisms involved in the pressure wave action within the engine, several pressure transducers have been located in the intake, crankcase, cylinder and exhaust.

A drivetrain model incorporating detailed crankshaft and drivetrain dynamics has been incorporated into an unsteady gas dynamic computer simulation of a single-cylinder two-stroke engine. This study examines the change in predicted engine performance caused by relaxing the conventional assumption of constant crankshaft velocity, and a comparison of results is presented. Relaxing the assumption changed the predicted brake mean effective pressures by over 10%. Experimental validation of the simulation involved mounting an engine to a test bed and driving an inertia wheel through a fully characterized drivetrain. A high-speed data acquisition system measured signals from a position encoder mounted on the crankshaft and from a non-contact torque transducer. The time and position data were used to calculate instantaneous crankshaft speed, and these results were compared to the predicted profiles. Simulation results and experimental measurements are presented and discussed.