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A computer simulation of a high performance two-stroke engine has been validated by a transient test method. The simulation included unsteady gas dynamics, together with detailed mechanical models for the reed valve, etc. The combustion model used Vibe coefficients derived directly from measured cylinder pressures. Cylinder scavenging characteristics which were measured on The Queen's University of Belfast (QUB) single-cycle rig were also incorporated in the simulation. Validation of the model involved use of an inertial dynamometer and data acquisition system which has been developed at QUB. This dynamometer incorporates a flywheel which is directly coupled to the engine. During a test, the engine is accelerated, and the torque and power are calculated from the flywheel speed characteristics. Further, at pre-determined engine speed intervals, the cylinder and exhaust pressures may be recorded. This testing system provided a convenient and rapid experimental method to acquire data.

The continued pursuit in Europe for lower emissions from transport vehicles now identifies several new areas to be targeted as their total emissions become ever more significant when compared to the continued decrease in automotive emissions. One such transport area that now faces pressure in the reduction of exhaust emissions, is the scooter/ moped market. The new ECE R47 cycle that governs the operational mode of the vehicle specifies a typical driving cycle over which the total emissions are collected and analysed. This paper evaluates a carburetted 50 cc moped over such a cycle and from the results ascertains the possibility of catalysing the exhaust gas to achieve acceptable limits. An empirical catalyst model is used to predict exhaust gas and substrate bed temperatures with the view to prolonging durability of the catalyst support. Results are presented for operating strategies which offer better long-term durability.

Small off-road engines (SORE) have been recognised as a major source of air pollution. It is estimated that non handheld SORE annually produce over 1 million tonnes of HC+NOx and over 50 million tonnes of CO2. The fuel system design and its operating AFR are of key importance with regard to engine operation and engine out emissions. The conventional low-cost float carburettors used in these engines are relatively ineffective at atomising and preparing the fuel for combustion requiring a rich setting for acceptable functional performance. EPA and CARB have confirmed that Phase 3 limits are achievable for a “durable” engine fitted with a conventional well calibrated and manufactured “stock rich setting” float carburettor together with catalytic oxidation after-treatment and passive secondary air injection.

In any internal combustion engine, the amount of heat rejected from the engine, and associated systems, is a result of the engine inefficiency. Successfully recovering a small proportion of this energy would therefore substantially improve the fuel economy. The Rankine Cycle system has been raising interest for its aptitude to produce systems capable of capturing part of this waste heat and regenerate it as electrical or mechanical power. By integrating these systems into existing hybrid engine environments, it has been proved that Rankine Cycle system, which is more than 150 years old, can play a major role in reducing fuel consumption. The use of such a system for waste heat recovery on a hybrid engine represents a promising compromise in transforming the thermal energy into electricity and feeding this electricity back to the vehicle drivetrain by using the in situ electrical motor system or storing it into batteries.

An experimental transient catalyst test rig has been developed and used to investigate the location and intensity of the reactions in a two-stroke oxidation catalyst as the inlet temperature is increased from ambient through light-off at a rate which is similar to that found in an engine exhaust after a cold start. The catalyst samples used in this apparatus are relatively large by plug flow reactor standards, (50mm diameter x 70mm long), which allows significant radial and axial variations in temperature and activity to occur. The gas and temperature readings recorded during these tests show that, even though the front face of the catalyst is hotter than the rear due to the transient temperature ramp, the highest reaction rate occurs in the rear half of the catalyst during the early stages of light-off. As the light-off process progresses, the reaction zone moves in a radial direction and migrates towards the front face.

This paper details a theoretical and experimental study of combustion phenomena within a two-stroke cycle, spark ignition engine. The theoretical part of the work involved the development of an improved quasi-dimensional combustion model. This model was incorporated into a computer program which was used to predict the thermodynamic and chemical changes occurring within a two-stroke engine during the closed cycle of the engine. The simulation uses a turbulent kinetic energy model to predict flame front velocity. Combustion chamber geometry is used to estimate entrained mass and mass fraction burned is calculated from a simple eddy-entrainment approach. The experimental work was undertaken to validate the combustion model. Two separate cylinder heads were designed with different combustion chambers and tested on a standard loop-scavenged engine over a range of operating conditions.

The internal combustion (IC) engines exploits only about 30% of the chemical energy ejected through combustion, whereas the remaining part is rejected by means of cooling system and exhausted gas. Nowadays, a major global concern is finding sustainable solutions for better fuel economy which in turn results in a decrease of carbon dioxide (CO2) emissions. The Waste Heat Recovery (WHR) is one of the most promising techniques to increase the overall efficiency of a vehicle system, allowing the recovery of the heat rejected by the exhaust and cooling systems. In this context, Organic Rankine Cycles (ORCs) are widely recognized as a potential technology to exploit the heat rejected by engines to produce electricity. The aim of the present paper is to investigate a WHR system, designed to collect both coolant and exhausted gas heats, coupled with an ORC cycle for vehicle applications.

The after-treatment of exhaust gas using 3-way catalytic converters is now normal practice in automotive applications. For other applications, such as outboards, motorcycles and utility engines, new legislation is now in place in both Europe and North America. Further reduction of the permitted emission levels require the use of catalysts for two-stroke engine applications. However, current automotive catalyst systems are not suitable for durable operation in most two-stroke engines and new analytical tools are required to aid the development engineers in the implementation of revised designs and operating strategies. This paper reviews the range of modeling techniques which have been developed for automotive uses and presents new and modified models suitable for two-stroke engines. This requires particular emphasis to be placed on the oxidation reactions that predominate in the two-stroke engine exhaust.

This paper describes the development and on-vehicle validation testing of next generation parallel hybrid electric powertrain technology for use in urban buses. A forward-facing MATLAB/Simulink powertrain model was used to develop a rule-based deterministic control system for a post-transmission parallel hybrid urban bus. The control strategy targeted areas where conventional powertrains are typically less efficient, focused on improving fuel economy and emissions without boosting vehicle performance. Stored electrical energy is deployed to assist the IC engine system leading to an overall reduction in fuel consumption while maintaining vehicle performance at a level comparable with baseline conventional IC engine operation.

Since its inception, the internal combustion (IC) engine has undergone continuous improvements with respect to efficiency and performance. Future regulatory and environmental requirements are not only driving still further improvements, but also extending the propulsion system efficiency through hybridization and potentially obsolescing the IC engine with hydrogen fuel cells. This paper describes the potential IC engine improvements to meet tomorrow’s challenges and the associated business and technical challenges in obtaining these challenges. The future propulsion system portfolio mix will encompass gasoline engines, diesel engines, hybrids and fuel cells. The critical role of the IC engine in this portfolio mix is examined.

With a transition towards electric vehicles for the transport sector, there will be greater reliance put upon battery packs; therefore, battery pack modelling becomes crucial during the design of the vehicle. Accurate battery pack modelling allows for: the simulation of the pack and vehicle, more informed decisions made during the design process, reduced testing costs, and implementation of superior control systems. To create the battery cell model using MATLAB/Simulink, an electrical equivalent circuit model was selected due to its balance between accuracy and complexity. The model can predict the state of charge and terminal voltage from a current input. A battery string model was then developed that considered the cell-to-cell variability due to manufacturing defects. Finally, a full battery pack model was created, capable of modelling the different currents that each string experiences due to the varied internal resistance.

In this paper a dynamic, modular, 1-D vehicle model architecture is presented which seeks to enhance modelling flexibility and can be rapidly adapted to new vehicle concepts, including hybrid configurations. Interdependencies between model sub-systems are minimized. Each subsystem of the vehicle model follows a standardized signal architecture allowing subsystems to be developed, tested and validated separately from the main model and easily reintegrated. Standard dynamic equations are used to calculate the rotational speed of the desired driveline component within each subsystem i.e. dynamic calculations are carried out with respect to the component of interest. Sample simulations are presented for isolated and integrated components to demonstrate flexibility. Two vehicle test cases are presented.

This paper describes an experimental comparison of loop and cross scavenged single-cylinder research engines. The cross scavenged engines have employed the QUB type deflector piston. The initial results show that the QUB cross scavenged engine exhibited inferior performance characteristics. Utilizing the QUB single cycle test rig, a study of the QUB cross scavenging system has shown that the bore-to-stroke ratio significantly influences the scavenging behaviour; reduction of the bore-to-stroke ratio from over-square values gave improved characteristics. On the basis of this finding, a new cross scavenged cylinder barrel was designed. In a subsequent series of dynamometer tests, improvements in power, fuel economy and emission characteristics were recorded for the new cylinder. These improved results approximate closely to those recorded for the loop scavenged engine and are considerably superior to those of the original cross scavenged cylinder.

The improvement in both performance and thermal efficiency of internal combustion engines at higher compression ratios is a well known phenomena. Indeed, a simple Otto Cycle analysis show a potential efficiency improvement of 13% by increasing the compression ratio from 9:1 to 15:1. However, the dilemma for engineers has always been in the realization of a practical operational mechanism. This paper describes the ECCLINK VCR mechanism which enables compression ratio to be altered within given limits on a running engine. A single cylinder 500 cm3 four-stroke research engine, incorporating the ECCLINK mechanism, has been built and tested. Results are presented at both full load and part load over a range of compression ratios, showing improvements in performance and fuel economy. Of particular interest is the fact that full load bsfc improvements equate to typical Otto cycle values.

This paper demonstrates the very useful technique of calculating air-to-fuel ratio, AFR, from exhaust gas emissions for a two-stroke cycle engine. Such methods are widely used for four-stroke engines where direct air flow measurement has now become redundant. Two modified methods are presented and compared with three standard methods, showing the accuracy to be quite good for a large set of test data from a standard two-stroke engine. A procedure for estimating AFR of the in-cylinder burning region, using trapping efficiencies, is presented for stratified charge engines, such as those with direct fuel injection. Accuracy of emissions measurement is assessed by calculating the total dry exhaust emissions, a method which could easily be automated for general test cell use. Finally, exhaust gas molecular weight and wet/dry ratio calculations are considered.

A mathematical model has been developed which predicts the tailpipe exhaust emissions of two-stroke cycle engines utilising an oxidising catalytic converter. This model is currently one-dimensional and has been developed as an aid to the design of engine/exhaust systems. The experimental rig employed has a two-fold function, its primary task was to aid in the validation of the model. Secondary to this it was used to simulate the gaseous properties of the exhaust gas at various positions in the exhaust system. The validation exercise is currently proceeding utilising metallic substrate technology with preliminary results indicating that the model is showing good correlation to measured values.

A quasi-dimensional computer simulation model is presented to simulate the thermodynamic and chemical processes occurring within a spark ignition engine during compression, combustion and expansion based upon the laws of thermodynamics and the theory of equilibrium. A two-zone combustion model, with a spherically expanding flame front originating from the spark location, is applied. The flame speed is calculated by the application of a turbulent entrainment propagation model. A simplified theory for the prediction of in-cylinder charge motion is proposed which calculates the mean turbulence intensity and scale at any time during the closed cycle. It is then used to describe both heat transfer and turbulent flame propagation. The model has been designed specifically for the two-stroke cycle engine and facilitates seven of the most common combustion chamber geometries. The fundamental theory is nevertheless applicable to any four-stroke cycle engine.