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This paper has two parts. The first compares the measured burned gas temperature using Coherent Anti-Stokes Raman Scattering (CARS) with the predictions of a multiple zone computer simulation of combustion. The second part describes a system that is capable of determining the heat flux into the combustion chamber by means of measuring the chamber surface temperature. It is shown that the multi-zone computer simulation can accurately predict the burned gas temperature once the fuel burn rate has been analyzed and the model tuned correctly. The effect of different fuels (methane and iso-octane) on the burned gas temperature is reported. A high burn rate or more advanced ignition timing gave a lower burned gas temperature towards the end of the engine cycle. The surface heat flux was deduced from measurements of the surface temperature by using a finite difference method.

A review of cycle-by-cycle variations in combustion and early flame histories is used to discuss the origins of cyclic variations in spark ignition engines. The hypothesis that cyclic variations are caused by the displacement of the flame kernel, is tested by means of a phenomenological turbulent entrainment combustion model. The model results are compared with experimental cycle-by-cycle combustion data, from a range of operating conditions that covers changes in: fuel, air fuel mixture, ignition timing and throttle setting. The combustion is characterised by the cycle-by-cycle variations in: the indicated mean effective pressure, the maximum pressure, the maximum rate of pressure rise, the burn rate and the flame speed. The model predicts correctly the effect of changes in the engine operating point on the cycle-by-cycle variations in combustion, and in many cases there is also good numerical agreement.

A phenomenological model of turbulent combustion has been developed and validated against data from wide ranging tests on a Ricardo E6 engine. Most tests used iso-octane, with a range of air fuel ratios and ignition timings, for tests at full throttle (with and without knock) and at part throttle. Some full throttle tests were also conducted with methanol and toluene. The engine performance was characterised by mean and coefficient of variation (CoV) of: the peak pressure, the maximum rate of pressure rise, the i.m.e.p., the burn rate and flame speed measurements. The results have been used to argue that the cycle-by-cycle variations in combustion should be characterised by the CoV of i.m.e.p. in preference to the CoV of the maximum cylinder pressure. Evidence is also presented to support the observation that the cycle-by-cycle variations in combustion are lower when the early combustion is more rapid.

This study investigates the wear characteristics of a variable valve timing (VVT) system used to vary the phasing of the inlet valve events on a medium speed marine diesel engine. The running-in properties of critical components within the system are examined. The effect of surface finish and surface hardness upon wear is examined. It was found that in order to prevent excessive wear between the roller and tappet follower then the roller should be harder than the tappet. Tappet and roller hardness values of 60 and 70 Rockwell Hardness ‘C’ (HRC) respectively were found to be satisfactory.

A program is described here that analyzes the behaviour of roller-follower valve gear. The motion is computed from a kinematic analysis; the instantaneous radius of curvature and the pressure angle are determined, so that the contact force and stresses can be evaluated at the cam/follower interface. The validation of the software is discussed. Also analyzed, is the hydrodynamic lubrication of the roller-follower journal bearing. A case study is described in which journal and bearing wear are attributed to inappropriately sited oil feed holes. It is shown that there is a region where no hydrodynamic pressure develops, thus providing an appropriate location for the oil feed holes. The assumptions in the hydrodynamic analysis are discussed.

A programme of work is being undertaken to improve the performance of a spark-ignited natural gas engine, that has been converted from a diesel engine. The aim of this work is to reduce the fuel consumption and NOx emissions. All experimental data and predictions refer to full throttle operation at 1500 rpm. The work to be reported here will include baseline tests that have been used to calibrate a two-zone combustion model. Particularly important are the predictions of the NOx emissions. The simulation has then been used to predict the effects of using: a higher compression ratio, and a faster burn combustion system. The design philosophy of the resulting fast burn combustion system is discussed, and some preliminary results are presented. There will be a discussion of the ignition parameters that affect the lean burn operation, and the effect of the spark plug gap position is discussed in the context of results from a phenomenological model of turbulent combustion.

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.

The influence of swirl on combustion in diesel and spark ignition engines is reviewed briefly, and this leads to a resumé of the swirl measuring techniques. The numerous ways of analysing swirl data are summarised and the relations between the different swirl parameters are presented. Experimental results are presented from a diesel engine in which the flow has been measured by a hot wire anemometer, a paddle wheel and a swirl torquemeter. The performance of the different measurement techniques is compared. Further results are presented (from a spark ignition engine) which illustrate the influence of the inlet port, manifold and entry conditions on the swirl measurements. Integration techniques are reviewed for producing a single swirl parameter to characterise the combined performance of the inlet port, valve and camshaft. Finally, the difficulty in standardising measurements of barrel swirl are discussed.

Induction tuning is now used on a wide range of spark ignition and diesel engines. It has also been the subject of research and publications over many years. The literature on induction tuning is reviewed here, and contradictions are identified and clarified. The use of resonator volume systems are also discussed and the various ways of modelling these systems are compared. In order to reconcile the differing theories, and to attempt to clarify the means by which induction tuning occurs, experiments have been undertaken with a single cylinder diesel engine. This was chosen as a single cylinder engine represents the simplest system, and a diesel engine does not have fuel in the induction system (which would otherwise modify the thermodynamic properties. The experimental measurements include the instantaneous air mass flow rate entering the induction system, and the pressure at the inlet port.

Different techniques for measuring air flows are reviewed briefly. It is shown that the induction system geometry as influenced for example by a flow meter can have a significant effect on the lean mixture limit. Results are also presented that illustrate the transient performance of a viscous flowmeter with unsteady flow. Since it is difficult to measure the air flow accurately, and the measurements can alter the engine performance, it is argued here that the air fuel ratio should be computed from an exhaust gas analysis. The influence of the assumptions and measurement errors on the computed air flow, are investigated for different fuel compositions and air fuel ratios.

This paper reviews the need for fast engine warm-up, and quantifies the fuel consumption penalty from cold engine operation, through an examination of vehicle usage and fuel consumption during warm-up. The conclusion is, that this is one of the few areas where there is still a potential (perhaps as high as 15%) for a reduction in overall fuel consumption. The reasons for poor engine performance during warm-up are discussed, and it is argued that the poor mixture preparation is the dominant effect. An experimental system is described, here, that has produced measurements of the heat fluxes from the combustion chamber, the heat transfer coefficient to the coolant, and key temperatures, for a range of operating points during warm-up. The heat flux and heat transfer coefficients are slightly dependent of the coolant temperature, but the observed trends are explained by reference to a correlation for convective heat transfer.