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An experimental study has been carried out to examine the influence of ring tan load and piston skirt modifications on piston assembly friction under motored engine conditions for initial temperatures of -20, 0 and 30°C and motoring speeds within the range 400 to 2000 rev/min. The study has been carried out using the block, crankshaft and pistons of a 2.4I, 4 cylinder diesel engine with a bore and stroke of 89.9mm and 94.6mm respectively. The pistons examined are typical of current designs for light duty diesels. A range of ring pack and piston skirt modifications have been tested, in each case as part of a complete piston assembly. The first changes produced reductions in fmep of between 5% and 38%. The reduction was due to improved skirt and ring pack designs in equal measure, each giving improvements of up to 20%. From this baseline eliminating the tan load of the piston rings was projected to give a further reduction in fmep of between 10% and 20%.

An experimental investigation has been carried out to compare the indicated performance and heat release characteristics of a DI diesel engine at compression ratios of 18.4:1 and 15.4:1. The compression ratio was changed by modifying the piston bowl volume; the bore and stroke were unchanged, and the swept volume was nominally 500cc. The engine is a single cylinder variant of modern design which meets Euro 4 emissions requirements. Work output and heat release characteristics for the two compression ratios have been compared at an engine speed of 300 rev/min and test temperatures of 10, -10 and -20°C. A more limited comparison has also been made for higher speeds representative of cold idle at one test temperature (-20°C). The reduction in compression ratio generally produces an increase in peak specific indicated work output at low speeds; this is attributable to a reduction in blowby and heat transfer losses and lower peak rates of heat release increasing cumulative burn.

An experimental study has been carried out to explore what limits fuel injection and EGR strategies when trying to run a PCCI-type mode of combustion on an engine with current generation hardware. The engine is a turbocharged V6 DI diesel with (1600 bar) HPCR fuel injection equipment and a cooled external EGR system. The variables examined have been the split and timings of fuel injections and the level of EGR; the responses investigated have been ignition delay, heat release, combustion noise, engine-out emissions and brake specific fuel consumption. Although PCCI-type combustion strategies can be effective in reducing NOx and soot emissions, it proved difficult to achieve this without either a high noise or a fuel economy penalty.

Kiva-3v Release 2 has been used to investigate combustion and emissions formation processes in a direct injection diesel engine with a high pressure common rail injection system. The influence of split main ratio and separation on NO and soot emissions have been of particular interest. Model validation has been based on comparisons with experimental data for heat release and engine-out emissions. Simulations have been carried out to explore the temporal development of combustion processes under typical part-load operating conditions. The results presented are for an engine speed and BMEP of 1600 rev/min and 6.76 bar, respectively.

DISI engine emissions and fuel economy are strongly dependent upon fuel injection and spark timings, particularly when the engine is operating in stratified charge mode. Experimental studies of the effects of injection and spark timings and the interaction between these are described. The sensitivity of HC and NOx emissions to timings during stratified charge operation, the comparison of performance under stratified and homogeneous charge modes of operation and the rationale for mode switch point settings are investigated. The high sensitivity of emissions to injection and spark timing settings gives rise to potential robustness issues. These are described.

An experimental study of the performance of a reverse tumble, DISI engine is reported. Specific fuel consumption and engine-out emissions have been investigated for both homogeneous and stratified modes of fuel injection. Trends in performance with varying AFR, EGR, spark and injection timings have been explored. It is shown that neural networks can be trained to describe these trends accurately for even the most complex case of stratified charge operation with exhaust gas recirculation.

A computational model has been developed to support investigations of temperature, heat flow and friction characteristics, particularly in connection with warm-up behaviour. A lumped capacity model of the engine block and head, empirically derived correlations for local heat transfer and friction losses, and oil and coolant circuit descriptions form the core of the model. Validation of the model and illustrative results are reported.

Two methods of determining the rate of heat transfer from the combustion chamber have been investigated. A First Law analysis is shown to be ill-conditioned because of sensitivity to heat release and gas property calculations. An alternative approach equates cycle-averaged chamber heat transfer to the difference between heat rejected to the coolant and gas heat transfer to the exhaust port. This has been examined as a basis for calibrating the Woschni correlation.

Spark plug fouling is a common problem when vehicles are repeatedly operated for very short periods, particularly at low temperatures. This paper describes a test procedure which uses a series of short, high-load drive cycles to assess plug fouling under realistic conditions. The engine is force cooled between drive cycles in order to increase test throughput. Spark plug resistance is shown to be a poor indicator of the effect of fouling on engine performance and the rate of misfiring is given as an alternative measure. An automated technique to detect misfires from engine speed data is described. This has been used to investigate the effect of spark plug type, fuelling level and spark timing on fouling. Spark plugs which are designed to run hotter are found to be more resistant to plug fouling. Isolated adjustments to fuelling level and spark timing calibrations within the range providing acceptable performance have a weak effect on susceptibility to plug fouling.

Spark ignition engines for automotive applications must have good cold start performance characteristics at sub-zero ambient temperatures. Satisfactory performance is most difficult to achieve at the lower end of the temperature range, typically around -30°C. The start characteristics of a particular engine depend on basic design features, starter motor characteristics, and the calibration and strategy used to regulate fuel supply during start up. The paper reports a computational model which enables the investigation of these with the minimum of experimental data. The model has been developed to run on desk-top PC machines, specifically as a CAE development tool. The formulation of the model and the experimental tests were used to generate the input data required for particular applications are described.

Optimising an engine specification to improve cold start performance has been investigated. Taguchi methods were used to define a test programme to assess the effect of seven build factors. Experiments were conducted to measure mixture ratio at the spark plug location after a short period of engine cranking at test conditions covering ± 15°C and three fuel-mass-supplied values. The analysis of the results identified build modifications which improved start quality and reduced HC and CO emissions substantially compared to a reference, base-line build. Injector design and location, and inlet valve timing were found to have most influence on robustness to uncontrolled variations in mixture preparation during starts.

The cycle-by-cycle variation of heat transferred per cycle (q) to the combustion chamber surfaces of spark ignition engines has been investigated for quasi-steady and transient conditions produced by throttle movements. The heat transfer calculation is by integration of the instantaneous value over the cycle, using the Woschni correlation for the heat transfer coefficient. By examination of the results obtained, a relatively simple correlation has been identified: This holds both for quasi-steady and transient conditions and is on a per cylinder basis. The analysis has been extended to define a heat flux distribution over the surface of the chamber. This is given by: where F(x/L) is a polynomial function, q″ is the heat transfer per cycle per unit area to head and piston crown surfaces and gives the distribution along the liner

Cycle-by-cycle pressure data have been recorded for a spark ignition engine operating over a wide range of steady state and perturbed running condition. The data base has been analysed to derive mass fraction burnt, pressure development and work mean effective pressure characteristics for individual cycles. Cross-correlation coefficients have been calculated to identify predominant relationships. The effect of combustion phasing on cross-correlation coefficients is particularly significant and three regimes of behaviour have been identified. These are associated with early, optimal and late cases. The cross-correlations between parameters derived from cycle-by-cycle data do not uniformly reflect trends seen between cycle-averaged values of these. Auto-correlation results have been examined for interactions between successive cycles with less success, although, again combustion phasing can have a significant influence on the strength of auto-correlation coefficients.

Engine Electronic Control (EEC) systems on spark ignition engines enable a high degree of performance optimisation to be achieved through strategy and calibration details in software, but development times and costs can be high. The range of functions performed by EEC systems, and the level of performance demanded, are increasing and new methods of development are required. In the paper, the use of neural networks in the development and implementation of open-loop control of air/fuel ratio during engine transient operating conditions is described. The investigation has addressed the definition of suitable networks, the procedure and data required to train these, and assessment of real-time performance of the implemented system. The potential benefits of the approach include reduced calibration effort and simplification of the control strategy.

A correlation for total gas-side heat transfer rate has been derived from the analysis of engine data for measured heat rejection rate, frictional dissipation, and published data on exhaust port heat transfer. The correlation is related to the form developed by Taylor and Toong, and the analysis draws on this. However, cylinder and exhaust port contributions are separated. Two empirical constants are fixed to best match predicted to measured results for heat rejection to coolant and oil cooler under steady-state conditions, and also for exhaust port heat transfer rates. The separated contributions also defined a correlation for exhaust port heat transfer rate. The description of gas-side heat transfer is suited to needs for the analysis of global thermal behaviour of engines.

A suite of computer programs for engine thermal analysis and the analysis of thermal interactions with external systems has been developed. Defining an engine design is made particularly simple and the representation generated agrees well with measured data. Engine geometry, mass, and internal coolant volume are determined from a short list of key parameters and the selection of a generic template. Thermal conditions in the engine structure are modelled numerically using the lumped-capacity method. Heat exchange at boundaries with gas, coolant and oil flows are described through sub-models giving good agreement with data for global characteristics of engine behaviour. The effects of spark timing and coolant composition on heat transfer rates are taken into account, as is the effect of frictional dissipation as a heat source. Validation and applications of the model are described.

Experimental studies of fuel utilisation during the early stages of engine warm-up after cold-starts are reported. The investigation has been carried out on a 1.81, 4 cylinder spark-ignition engine with port electronic fuel injection. The relationship between fuel supplied and fuel accounted for by the analysis of exhaust gas composition shows that a significant mass of fuel supplied is temporarily stored or permanently lost. An interpretation of data is made which allows time-dependent variations of these to be separately resolved and estimates of fuel quantities made. The data covers a range of cold-start conditions down to -5°C at which, on a per cylinder basis, fuel stored peaks typically at around 0.75g and a total of 1g is returned over 100 seconds of engine running. Fuel lost past the piston typically accounts for 2g over 200 to 300 seconds of running.

The paper reports the design of a model and HIL system produced to support the development and testing of Electronic Control Unit/Engine Management System (ECU/EMS) software for a V6 turbo-charged automotive diesel engine. The engine model, developed in Simulink, is compiled to execute on a dSpace platform and interacts with the ECU/EMS module in real time. The main features of the engine model are outlined. The configuration of the model and HIL components are described, and the performance of the system is illustrated and discussed. Practical decisions on the inclusion of real or virtual sensors and actuators, and other implementation issues, are explained. Recent and potential future applications of the system are described.

The paper outlines experimental investigations of fuel injection strategies which are possible using high pressure common rail fuel injection systems. Strategies using a split main with a pilot injection have been explored. The strategy variables were the ratio of the first to second part of the main, the separation between these and the timing of the start of main injection. Exhaust gas recirculation rate was a fourth variable. Pilot injection quantity and timing, and rail pressure were held constant. The influence on emissions and specific fuel consumption is described and the method of optimising settings is outlined. The manipulation of fuel injection settings to best meet optimisation targets for emissions and specific fuel consumption is described. The benefits compared to results for optimised single main injection are described, as are issues of strategy robustness.

The deterioration of combustion stability as lean operating limits and misfire conditions are approached has been investigated experimentally. The study has been carried out on spark ignition engines with port fuel injection and four-valves-per-cylinder. Test conditions cover fully-warm and cold operation, and ranges of air/fuel ratio, exhaust gas recirculation rates and spark timing. An approximate method of calculating gas/fuel ratio is described. This is used to show that combustion stability, characterised by the coefficient of variation of i.m.e.p., is a function of calculated gas/fuel ratio and spark timing until near to the limit of stability. A rapid deterioration in stability and the onset of weak, partial burning occurs at a gas/fuel ratio between 24:1 and 26:1 under fully-warm operating conditions, and around one gas/fuel ratio lower under cold operating conditions.