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The last decade has seen a rapid increase within industry of the use of computational fluid dynamics (CFD) to assist in the design and development phase of product manufacture. There have recently evolved many new commercial CFD codes, both general and problem specific, but little validation data is available with which the engineer may assess the code's ability to simulate accurately a given flow problem. Much doubt prevails about current methods of turbulence modelling yet without comparison with experimental data few firm conclusions may be drawn. The work described in this paper is an investigation into the highly turbulent air flow through a vehicle intercooler duct. The general purpose CFD code STAR CD was used to obtain a computational prediction of the flow field. These results were correlated with experimental values of velocity and turbulence levels obtained using a single component laser Doppler anemometry system.

In both the marine and power industries there are now a choice of off-the-shelf condition monitoring systems available that utilise artificial intelligence techniques to analyse engine performance data. These systems are proving to be a valuable aid in optimising performance and reducing down-time by assisting with maintenance planning. These systems rely on careful monitoring of an engine's performance, for instance engine speed, fuelling, boost pressure, turbine inlet pressure, turbocharger speed, and exhaust temperature. With this data, they utilise a variety of interpolation and pattern recognition algorithms to compare it with previously recorded data stored in lookup tables. This paper describes how a neural network approach can be used as a cheap alternative for the analysis of this data, greatly reducing the need for such large lookup tables and complex pattern recognition programs.

A Variable Valve Timing system has been designed and rig tested for application on a high speed marine diesel engine. It has been demonstrated that inlet valve phasing is an appropriate way of reducing the flow of exhaust gas residuals, particularly at light loads, into the inlet manifold during valve overlap. The system described controls the position of the roller follower by means of an eccentric to allow the inlet valve events to be retarded by up to 40° crank angle. A kinematic model has been constructed to examine the tappet motion, and comparisons are made with measured values. Modelling of the lubrication regime at the roller, cam and tappet contact points is presented, to examine the system wear characteristics. Roller follower speed is measured to examine the prevailing lubrication regime. Rig results show that the VVT system is reliable and that the desired phasing of the valve events is obtained.

A single cylinder research engine has been installed at Bath University for investigation of a stratified charge combustion system for a natural gas engine. The engine has simulated turbocharging and a compressed mains natural gas supply. A relatively complex fuelling system has been developed to enable independent control and measurement of air-fuel ratio to each of the engine's combustion chambers. Results indicate that the emission of oxides of nitrogen may be reduced to very low levels (1-2g/kWh) compared with conventional stoichiometric gas engines (10-2Og/kWh). It has been found that the operation of the prechamber can influence the level of exhaust emission and the cyclic dispersion. Optimum performance is achieved within a relatively narrow range of prechamber supply air:gas ratio from 3:1 to 8:1 by mass. A multi-dimensional fluid dynamic model of the prechamber was developed and used to study the in-prechamber flow structure and mixing processes.

The paper describes a compact low cost engine simulator used in a diagnostic system for marine diesel engines. It models normal and certain abnormal behaviour modes and can be used with an intelligent health monitor for fault recognition. The mathematical model used is the highly detailed ‘filling and emptying’ method wherein the first order equations which result from the principles of energy, mass and momentum conservation are solved on a degree by degree basis. This allows a number of faults to be simulated, for example, those which affect the airflow such as leaking intake or exhaust manifolds or fouled turbomachines or intercoolers. A multiprocessor Motorola 68020 computer system is used to allow concurrent solution of the equations for each of the thermodynamic control volumes.

The paper presents the first phase of a research project to study the relationship between valve design parameters and the performance of turbocharged truck engines. The results discussed were produced by computer simulation of the diesel engine and its associated intercooler and turbocharger. Three aspects of exhaust valve design are studied : the rate of valve opening, the size of the exhaust valve in relation to the inlet valve and the timing of the exhaust valve opening event. Rate of exhaust valve opening is found to be an important influence on exhaust pulse energy and may Drovide a means of increasing low-speed boost. Valve area ratio had only a small effect on engine performance over the range studied (0.8 ≤ AI /AE ≤1.2), whereas the timing of exhaust valve opening proved to be an important parameter, having a significant effect on the thermal efficiency of the system.

THE PAPER presents the findings of a combined experimental and theoretical investigation of jet mixing phenomena in quiescent or swirling flow fields, using the hydraulic analogue technique to simulate the Diesel injection process, with particular emphasis on the development of wall jets. The photographic records clearly indicate the propagation and mixing associated with the advancing jet and provide a basis for quantitative analysis of trajectories and entrainment rates. The mathematical models, while based on simplified solutions, nevertheless model the observed processes with satisfactory accuracy.