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Vehicle manufacturers face mounting pressure to increase fuel economy and reduce vehicle tailpipe emissions in order to reduce the environmental impact of their vehicles and to meet ever more stringent regulations. Wrightbus have developed first generation single– and double–deck Hybrid Electric Vehicle (HEV) city buses, a number of which are in regular service in London and other cities. These buses utilise a series hybrid powertrain with a turbo-diesel engine, drive motors with total output powers between 120 kW and 170 kW and a DC electrical storage system. Fuel savings up to 30% have been achieved in service. This paper presents a literature review of hybrid vehicle modelling, and covers the work completed by Queen's University to create a software model of the Wrightbus HEV drivetrains in the Mathworks Mat-lab/Simulink environment. The model has been calibrated to several drivetrain configurations, including differing battery technologies, control systems and vehicle hardware.

The incorporation of one-dimensional simulation codes within engine modelling applications has proved to be a useful tool in evaluating unsteady gas flow through elements in the exhaust system. This paper reports on an experimental and theoretical investigation into the behaviour of unsteady gas flow through catalyst substrate elements. A one-dimensional (1-D) catalyst model has been incorporated into a 1-D simulation code to predict this behaviour. Experimental data was acquired using a ‘single pulse’ test rig. Substrate samples were tested under ambient conditions in order to investigate a range of regimes experienced by the catalyst during operation. This allowed reflection and transmission characteristics to be quantified in relation to both geometric and physical properties of substrate elements.

The most common mode of deactivation suffered by catalysts fitted to two-stroke engines has traditionally been thermal degradation, or even meltdown, of the washcoat and substrate. The high temperatures experienced by these catalysts are caused by excessively high concentrations of HC and CO in the exhaust gas which are, in turn, caused by a rich AFR and the loss of neat fuel to the exhaust during the scavenging period. The effects of catalyst poisoning due to additives in the oil is often regarded as a secondary, or even negligible, deactivating mechanism in two-stroke catalysts and has therefore received little attention. However, with the introduction of direct in-cylinder fuel injection to some larger versions of this engine, the quantities of HC escaping to the exhaust can be reduced to levels similar to those found on four-stroke gasoline engines.

A technique has been developed to study the axial static pressure profile through the channels of a 400 cells per square inch (cpsi) catalytic converter monolith. The shape of the profile proved different from the accepted laminar flow profile, although the flow conditions are clearly laminar within the channels of the converter. The fact that the inner surfaces of the channels are extremely rough, and that this roughness is highly irregular, is thought to have an effect on the developed pressure profile. The measured profile was compared against the pressure profiles predicted by the most popular models in the published literature. A two-point criterion was developed to distinguish among those models. It was observed that Shah's model [1]* for the pressure drop along a square duct is the most appropriate. Additional static pressure measurements were taken both before and after the catalyst element and used to calculate the entrance and exit total pressure loss coefficients.

Stratified scavenging has been applied to two-stroke engines to improve fuel consumption and reduce exhaust emissions. To evaluation how this is achieved a stratified scavenging process was simulated using a three-gas single-cycle scavenging apparatus. The experiment simulated the fuel stream entering the rear transfer port of a five port cylinder and air streams entering the remaining ports. The scavenging efficiency and fuel trapping are calculated after the cycle by examining the cylinder contents. The design of the apparatus is particularly suited to investigating cylinder design changes during the prototype stage of engine development. A simulation of the stratified scavenging experiment using the Computational Fluid dynamics (CFD) code VECTIS, showed good correlation with measured results. The simulation provides a real insight into the cylinder flow behaviour of the separate fuel and air streams entering the cylinder.

The advantages of high power to density ratio and low manufacturing costs of a two-stroke engine compared to a four-stroke unit make it currently the most widely used engine type for 50cc displacement 2-wheelers. This dominance is threatened by increasingly severe exhaust emissions legislation, forcing manufactures to develop their two-stroke engines to comply with the legislation. This paper describes a simple solution to reduce these harmful emissions in a cost effective manner, for a scooter application. The method of stratified scavenging is achieved by delivering the fuel into the rear transfer passage from a remote mechanical fuel metering device, operated by intake manifold pressure. Air only is delivered into the cylinder from the remaining transfer passages which are directed towards the rear transfer port, thus impeding the fuel from reaching the exhaust during the scavenging process.

This paper describes an experimental investigation into the effect of bore/stroke ratio on a simple two-stroke engine. This was achieved with a special purpose engine of modular design. The engine allowed four combinations of bore and stroke to be contrived to yield a common swept volume of 400 cm3 with bore/stroke ratios of: 0.8, 1.0, 1.2 and 1.4. Other factors that might affect engine performance were standardised: the exhaust, intake and ignition systems were common, the combustion chamber designs were similar, scavenge characteristics were similar, port timings and time-areas were kept the same, and cylinder and crankcase compression ratios were also kept the same. The most important conclusions were: Engine power was greatest with the compromise bore/stroke ratio of 1.0 or 1.2. Combustion efficiency tended to decrease with increasing bore/stroke ratio. Mechanical efficiency tended to increase with increasing bore/stroke ratio.

Due to increasingly stringent emissions legislation the four-stroke engine is beginning to replace the two-stroke engine for motorcycle and scooter applications over 50cc. However, because of its comparatively poor performance, the four-stroke unit is not replacing the two-stroke for moped applications which are restricted to 50cc. To meet forthcoming European legislation the two-stroke moped engine requires an exhaust catalyst which presents considerable durability problems when applied to this type of engine. This would not be the case with a four-stroke unit, so if its performance could be improved it would be an attractive alternative. This paper illustrates the difficulties facing four-stroke engines of this size, the improvements required, the benefits (and problems) of a multi-valve approach and possible means of improving performance.

One-dimensional (1-D) modelling codes are now commonplace in engine simulation programs. Thermodynamic analysis associated with the unsteady gas flow through engine ducting is an important element within the modelling process. This paper reports on a new approach in analysing mass and energy transport through a pipe system using the mesh method. A new system has been developed for monitoring wave energy and gas properties, using a two-dimensional grid to represent the time-mesh boundary domain. This approach has allowed for refinement of the current mesh method by allowing more accurate monitoring of gas properties. The modified method was tested using measured results from a Single-Shot Rig. A CFD analysis was also conducted and compared with the new method. The new method performed very well on the range of pipe geometries tested.

With the legislative demands increasing on recreational vehicles and utility engined applications, the two-stroke engine is facing increasing pressure to meet these requirements. One method of achieving the required reduction is via the introduction of a catalytic converter. The catalytic converter not only has to deal with the characteristically higher CO and HC concentration, but also any oil which is added to lubricate the engine. In a conventional two-stroke engine with a total loss lubrication system, the oil is either scavenged straight out the exhaust port or is entrained, involved in combustion and is later exhausted. This oil can have a significant effect on the performance of the catalyst. To investigate the oiling effect, three catalytic converters were aged using a 400cm3 DI two-stroke engine. A finite level of oil was added to the inlet air of the engine to lubricate the internal workings. The oil flow rate is independent of the engine speed and load.

Washcoat sintering and substrate meltdown have traditionally been the principle deactivating mechanisms of catalysts fitted to two-stroke engines. The reduction of the excessively high HC and CO levels responsible for these effects has therefore been the focus of considerable research which has led to the introduction of direct in-cylinder fuel injection to some larger versions of this engine. However, much less attention has been paid to the effects of oil and its additives on the performance and durability of the two-stroke catalyst. The quantity of oil emitted to the exhaust system of the majority of two-stroke engines is much greater than in four-stroke engines of comparable output due to the total loss lubrication system employed. The fundamental design of the two-stroke also permits some of this oil to ‘short-circuit’ to the exhaust in a neat or unburned form.

Analysis of pressure traces from within the cylinder of IC engines is a long established technique, particularly in automotive applications. This approach allows burn rate data to be calculated from the shape of the pressure traces, providing direct combustion information to development engineers. With the proliferation of high-powered and low-cost computers, recording of pressure traces and analysis to give burn rates are now becoming standard measurements. However, this is still a complex technique, which is very open to error and prone to misinterpretation of results. This is particularly relevant for two-stroke engines where cyclic variations can be high and traces can be difficult to analyze. This paper considers the standard techniques available for pressure trace analysis, highlighting the areas for problems and outlining good practice for reliable and accurate measurement.

The two-stroke engine, by its nature is very dependent on the unsteady gas dynamics within an exhaust system. This is demonstrated by the tuning effects on two-stroke engines, which have been well documented. In consideration of current emissions legislation, a two-stroke engine can be fitted with a catalytic converter for the outboard, utility or automotive markets. The catalytic substrate represents a major obstruction to the flow of exhaust gas, which hinders the progression of the main exhausted pulse, and in turn effects the scavenging of the cylinder and ultimately the performance of the engine. Within this investigation, a 400 cc direct injection two-stroke engine was used with various catalysts positioned at different distances from the exhaust manifold. Comparison tests were performed between a fully lit off catalyst and a non-operational bare substrate.

This paper details the investigation of the properties of inlet gases and shows how they affect the flow patterns immediately in front of the catalyst and the subsequent loss of efficiency. A thorough analysis of the flow distribution at the inlet of the catalyst enabled the effective catalyst diameter to be calculated. Subsequent calculations were then carried out to determine the loss of catalyst function through flow maldistribution. Experimental work involved flowing engine proportioned amounts of air through canisters of a fixed geometric profile containing a catalyst. Inlet cones of angles 10°, 15° and 45° were flowed to estimate the effect of the cone design on the velocity distributions at the face of the catalyst. Simple geometric profiles were investigated to allow a thorough understanding of the mechanism of flow to be comprehended and its affect on catalyst conversion to be analysed.

The emissions produced from a simple carburetted crankcase scavenged two-stroke cycle engine primarily arise due to losses of fresh charge from the exhaust port during the scavenging process. These losses lead to inferior fuel consumption and a negative impact on the environment. Pressure on exhaust emissions and fuel consumption has reduced the number of applications of the two-stroke cycle engine over the years, however the attributes of simplicity, high power density and potential low manufacturing costs have ensured its continuing use for mopeds and motorcycles, small outboard engines and small utility engines. Even these last bastions of the simple two-stroke engine are being challenged by the four stroke alternative as emissions legislation becomes tighter and is newly formulated for many categories of engines. A simple solution is described which reduces short circuit and scavenge losses in a cost effective way.

This paper reports on the preliminary investigation of the identification of a method to model the transient operation of a single cylinder four-stroke gasoline engine. During a transient the response of an engine and the actual fuel mixture delivered to the engine are significantly affected by the behaviour of the fuel injected into the inlet manifold. In the past, different wall-wetting theories have been developed to model and attempt to resolve this problem and one of the most definitive is investigated here along with two other theories developed at QUB. A steady state computer model of a single cylinder four-stroke spark-ignition research engine was written and validated. The three different wall-wetting theories were studied and each individually integrated into the steady state model. This allowed simulated transients to be performed on the computer and the results generated to be compared with firing transient tests.

Anaerobic digestion is a popular method of treating sewage sludge. Biogas or sewage gas is a by-product of this process. Significant volumes of biogas are produced at many sewage treatment works and also at some landfill sites from the natural breakdown of municipal waste. This biogas can be used as a fuel for an engine and generating set, producing electrical power and heat. A multi-cylinder two-stroke cycle system, capable of being retrofitted to current production four-stroke cycle engines, is proposed, primarily for the combustion of biogas in combined heat and power applications. The engine incorporates features to give good tolerance to the corrosive agents associated with biogas. This paper describes the design and initial development of a purpose built single cylinder research engine to investigate this concept. A low pressure direct injection system which has been developed for use with the engine is also outlined.

A study of fuel injection during the open cycle of a small spark ignition two-stroke cycle engine has been carried out. A manually controlled electronic fuel injection system has been used as this appears to have many advantages over mechanically controlled equipment. Various injection locations were considered and injection timing and air/fuel ratio varied at each position to determine optimum power and bsfc requirements. The results presented are compared with baseline carburation and with fuel injection into the intake to assess the potential improvements gained from each injector location.

This paper deals broadly with three aspects of the fatigue substantiation of general aviation aircraft structures. It describes the development of the Australian fatigue substantiation requirements for general aviation aircraft; it presents the results of local work in the acquisition of loads spectra for a range of aircraft, including pressurized and nonpressurized light twins, and it discusses some specific problems affecting the safe life and fail-safe substantiation of general aviation aircraft structures. Recent Australian work on ground taxi load spectra and on the endurance and radiographic inspectability of laminated spar caps is described.