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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 unsteady gas dynamic phenomena in a racecar airbox have been examined, and resonant tuning effects have been considered. A coupled 1D/3D analysis, using the engine simulation package Virtual 4-Stroke and the CFD package FLUENT, was used to model the engine and airbox. The models were experimentally validated. An airbox was designed with a natural frequency in the region of 75 Hz. A coupled 1D/3D analysis of the airbox and a Yamaha R6 4-cylinder engine predicted resonance at the single-cylinder induction frequency; 75 Hz at an engine speed of 9000 rpm. The amplitude of the pressure fluctuation was found to be influenced by the separation between the intake pipes in the airbox. For an n-cylinder even-firing engine, if the intakes are coincident in the airbox, then the fundamental and all harmonics of the forcing function, apart from the (n-1)th, (2n-1)th, etc. will cancel. That is, only the multi-cylinder induction frequency and its multiples will not cancel.

The unsteady gas dynamic phenomena in engine intake systems of the type found in racecars have been examined. In particular, the resonant tuning effects, including cylinder-to-cylinder power variations, which can occur as a result of the interaction between an engine and its airbox have been considered. Frequency analysis of the output from a Virtual 4-Stroke 1D engine simulation was used to characterise the forcing function applied by an engine to an airbox. A separate computational frequency sweeping technique, which employed the CFD package FLUENT, was used to determine the natural frequencies of virtual airboxes in isolation from an engine. Using this technique, an airbox with a natural frequency at 75 Hz was designed for a Yamaha R6 4-cylinder motorcycle engine. The existence of an airbox natural frequency at 75 Hz was subsequently confirmed by an experimental frequency sweeping technique carried out on the engine test bed.

Computational Fluid Dynamics (CFD) is frequently used to predict complex flow phenomena and assist in engine design and optimization. The scavenge process within a 2-stroke engine is key to engine performance especially in high performance racing applications. In this paper, FLUENT CFD code is used to simulate the scavenging process within a 125cc single cylinder racing engine. A variety of different port designs are simulated and scavenge characteristics compared and contrasted. The predicted CFD results are compared with measured scavenge data obtained from the QUB single-cycle scavenge rig. These results show good agreement and provide valuable insight into the effect of port design features on the scavenging process.

The single shot apparatus creates a pressure wave (compression or rarefaction) by releasing a pressure or vacuum from a blowdown cylinder. The wave is contrived to be representative of cylinder blowdown or the suction wave that emanates from an engine intake valve during induction. Generated waves may be fired into a quiescent pipe or system of pipes that represent the ducts found on an engine. The most significant features that distinguish the new apparatus from any previous are that it uses a poppet valve to release the wave and that the apparatus is largely automatic, enabling the generation of a new wave every 15 seconds or so. The particular version of the apparatus described here has been conceived to allow a low speed background flow to be maintained in the pipe system between waves. The purpose of this is to allow microscopic particles to be kept in suspension in the air to facilitate flow studies using Particle Image Velocimetry (PIV) or Laser Doppler Anemometry (LDA).

Engine cycle simulation is an essential tool in the development of modern internal combustion engines. As engines evolve to meet tougher environmental and consumer demands, so must the analysis tools that the engineer employs. This paper reviews the application of such a tool, VIRTUAL 4-STROKE [1], in the modelling of a benchmark 1.9 Litre TDI engine. In an earlier paper presented to the Society [2] the authors presented results of a validation study on the same engine under full load operation. This paper expands on that work with validation of the simulation model against measured data over a full range of part load operation.

This paper describes a technique whereby race car airbox performance can be assessed directly in terms of predicted engine performance by coupling a one-dimensional engine model on a timestep-by-timestep basis to a three-dimensional computational fluid dynamics (CFD) model of an airbox. A high-performance three-litre V10 engine was modelled using Virtual 4-Stroke unsteady gas dynamics engine simulation software, while two airbox configurations, representative of those used in FIA Formula 1 (F1), were modelled using general purpose CFD software. Results are presented that compare predicted engine performance for the two airbox geometries considered in the coupled simulations. Individual cylinder performance values are also presented and these show significant variations across the ten cylinders for each airbox simulated.

Recent environmental legislation to reduce emissions and improve efficiency means that there is a real need for improved thermodynamic performance models for the simulation of direct-injection, turbocharged diesel engines, which are becoming increasingly popular in the automotive sector. An accurate engine performance simulation software package (VIRTUAL 4-STROKE) is employed to model a benchmark automotive 1.9-litre Turbocharged Direct Injection (TDI) diesel engine. The accuracy of this model is scrutinised against actual test results from the engine. This validation includes comparisons of engine performance characteristics and also instantaneous gas dynamic and thermodynamic behaviour in the engine cylinders, turbocharger and ducting. It is seen that there is excellent agreement in all of these areas.

The paper discusses the application of maps of measured discharge coefficients for poppet valves, cylinder ports, and in-pipe throttles within a theoretical simulation of the unsteady gas flow through an internal combustion engine. The maps provided cover both inflow and outflow at the discontinuity being discussed and are displayed as contour maps of the discharge coefficient as some function of the geometrical flow area of that discontinuity and of the pressure ratio across it up to a maximum value of 2.0. An engine simulation package is used for both a four-stroke and a two-stroke engine to determine the typical pressure ratio and area ratio characteristics which pertain at all such discontinuities at representative engine speed and load conditions.

At the 1999 SETC meeting, a paper presented a simple, tuned and silenced exhaust system for a two-stroke engine which theoretically reduced both noise and exhaust emissions and increased engine power and fuel efficiency. In this paper that design concept is applied to a small 56 cc industrial engine and experimentally shown to deliver the projected behaviour which was predicted in that earlier publication. Experimental test results are presented for power output, fuel consumption, and exhaust emissions to illustrate these statements. An accurate engine simulation software package (VIRTUAL 2-STROKE) is employed to model the entire two-stroke engine and to demonstrate not only its effectiveness as a design tool in this area but also that it can accurately predict the above-mentioned performance and emission characteristics.

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.

An experimental and theoretical investigation to minimise the hydrocarbon emissions from a 25 cm3 two-stroke engine with finger transfer ports is described. Finger ports have the side of each passage closest to the cylinder axis open to the cylinder bore making it possible to produce high-pressure die castings with the simplest of dies. Cylinders utilising this type of porting are believed to have inferior scavenging characteristics compared to those using closed or cup-handle porting. The effects of cylinder scavenging characteristics and port optimisation on engine performance were examined using a computer simulation. It is concluded that there is potential for a 70% reduction in exhaust hydrocarbon emissions through scavenging efficiency improvements and port optimisation, provided the cylinder scavenging can be developed to match that of the best existing unconventional crossflow scavenged designs.

A combined one-dimensional, multi-dimensional computational fluid dynamic modelling technique has been developed for analysis of unsteady gas dynamic flow through automotive mufflers. The technique facilitates assessment of complex designs in terms of back-pressure and noise attenuation. The methodology has been validated on a number of common exhaust muffler arrangements over a wide range of test conditions. Comparison between measured and simulated data has been conducted on a Single-Pulse (SP) rig for detailed unsteady gas dynamic analysis and a Rotary-Valve (RV) rig in conjunction with an anechoic chamber for noise attenuation analysis. Results obtained on both experimental arrangements exhibit excellent gas dynamic and acoustic correlation. The technique should allow optimisation of a wide variety of potential muffler designs prior to prototype manufacture.

One-dimensional (1-D) unsteady gas dynamic models of a number of common muffler (or silencer) elements have been incorporated into a1-D simulation code to predict the impact of the muffler on the gas dynamics within the overall system and the radiated Sound Pressure Level (SPL) noise spectrum in free-space. Correlation with measured data has been achieved using a Single-Pulse rig for detailed unsteady gas dynamic analysis and a Rotary-Valve rig in conjunction with an anechoic chamber for noise spectra analysis. The results obtained show good agreement both gas dynamically and acoustically. The incorporation of these models into a full 1-D engine simulation code should facilitate the rapid assessment of various muffler designs prior to prototype manufacture and testing.

This paper reports on the experimental evaluation of certain aspects concerning the mathematical modelling of pressure wave propagation in engine ducting. A particular aspect is the coefficient of discharge of the various ports, valves or apertures of the ducting connected to the cylinder of an engine or to the atmosphere. The traditional method for the deduction of the coefficients of discharge employs steady flow experimentation. While the traditional experimental method may well be totally adequate, it is postulated in this paper that the traditional theoretical approach to the deduction of the discharge coefficient from the measured data leads to serious inaccuracies if incorporated within an engine simulation by computer. An accurate theoretical method for the calculation of the discharge coefficient from measured data is proposed.

This paper reports on the first phase of an experimental evaluation of four different methods for the mathematical modelling of unsteady gas flow in a pipe system containing an area discontinuity. The four methods under investigation are the non-homentropic method of characteristics, the two-step Lax-Wendroff method with flux corrected transport, the Harten-Lax-Leer upstream difference method and the GPB finite system method. The experimentation is conducted using the QUB SP (single-pulse) pressure wave generator consisting of a cylinder, connected via a sliding valve to a long duct. The pressure waves it creates closely mimic those to be found in i.c. engines. The initial cylinder pressure may be set to simulate either an induction or an exhaust process. Various ducts are attached to the pressure wave generator to simulate both sudden and gradual area changes. Each duct is sufficiently long as to permit pressure wave observation without superposition effects.

This paper reports on the experimental evaluation of certain aspects of the mathematical modelling by the GPB method of pressure wave propagation through finite systems, of unsteady gas flow in engine ducting. The aspects under examination are the propagation of pressure waves through a pipe which contains gases of dissimilar properties. In this case the gases are carbon dioxide and air. The experimentation is conducted using the QUB SP (single pulse) pressure wave generator consisting of a cylinder, connected via a sliding valve to a long duct. The pressure waves it creates closely mimic those to be found in i.e. engines. The initial cylinder pressure may be set to simulate either an induction or an exhaust process, but the experiments reported here are of compression waves only. The duct attached to the pressure wave generator is a straight pipe. The cylinder and part of the pipe are filled with carbon dioxide and air.

This paper reports on the use of mathematical modelling by the GPB method of pressure wave propagation through finite systems, for the design of prototype exhaust systems and silencers for a Harley-Davidson motorcycle. The motorcycle engine is the classic 1340 cm3 45° V-twin power unit. The design objectives were to gain mid-range power and torque without loss of performance at either end of the speed range and to design silencers which would enhance the performance and the noise image of the machine. The Queen's University of Belfast (QUB) (3)* employed their unsteady gas flow modelling techniques to the design of the system and its silencers to complement a new camshaft design from Crane Cams. The results of the use of these computer based design techniques are reported as performance characteristics of power and torque for the new design by comparison with the stock system.

This paper reports on the first phase of an experimental evaluation of five different methods for the mathematical modelling of unsteady gas flow in engine ducting. The five methods under investigation are the homentropic method of characteristics, the non-homentropic method of characteristics, the two-step Lax-Wendroff method with flux corrected transport, the Harten-Lax-Leer upstream difference method and the Blair method of pressure wave propagation through finite spaces. A single cycle pressure wave generator consisting of a cylinder, connected via a sliding valve to a long duct, has been designed and built. The pressure waves it creates closely mimic those to be found in i.e. engines. The cylinder and the ducts of the device can be filled with any gas and at elevated temperatures. A perfect seal exists between the cylinder and the valve thus enabling mass- flow correlation. The initial cylinder pressure may be set to simulate an induction or an exhaust process.

LDV is used to measure steady flow in a two port loop scavenged model two-stroke engine cylinder. The model cylinder, machined from acrylic for maximum optical access, is geometrically identical to that used in a previous dynamic study of transfer port efflux vectors. The measured flow field is compared with a CFD prediction which employs experimentally measured velocity, mass flow rate, and turbulence intensity as the inlet boundary condition at the transfer port. The finite volume prediction, using the PHOENICS general purpose code recreates the global flow pattern well, but shows some local discrepancies in flow direction and magnitude. Levels of turbulent kinetic energy were poorly recreated using a k-ϵ model of turbulence, especially around impingement of the incoming jets where local errors of up to 60% were seen.