P. J. Shayler

Contributions to engine friction during cold, low speed running and the dependence on oil viscosity

Friction data have been acquired from motored engine tests on four designs of light duty automotive diesel engines with a swept capacity around two litres (1.81-2.21). The data cover temperatures at the start of motoring of -20°C and above, and motoring speeds from 200 rev/min to 1000 rev/min. Most tests were carried out using SAE 10W/30 oil. The breakdowns separated piston assembly, crankshaft assembly, valve train and auxiliary component contributions to friction mean effective pressure (fmep). The empirical coefficients and functions used in the engine friction model developed by Patton, Nitschke and Heywood (SAE 890836) have been modified to fit the low speed, low temperature test data without greatly affecting predictions for fully-warm conditions. The dependence of component contributions on oil viscosity during warm-up has been taken into account.

The exploitation of neural networks in automotive engine management systems

Abstract The use of electronic engine control systems on spark ignition engines has enabled a high degree of performance optimisation to be achieved. The range of functions performed by these systems, and the level of performance demanded, is rising and thus so are development times and costs. Neural networks have attracted attention as having the potential to simplify software development and improve the performance of this software. The scope and nature of possible applications is described. In particular, the pattern recognition and classification abilities of networks are applied to crankshaft speed fluctuation data for engine-fault diagnosis, and multidimensional mapping capabilities are investigated as an alternative to large ‘lookup’ tables and calibration functions.

Characterizing the effect of viscosity on friction in the piston assembly of internal combustion engines

Abstract The friction mean effective pressure (fmep) contribution of piston assemblies running under motored engine conditions in cylinders with plateau or laser honed bores has been investigated. Results have been obtained for engine speeds in the range 400-2000 r/min and temperatures from -20 to around 60°C. The fmep of the piston assembly is observed to depend most directly on oil viscosity evaluated at the temperature of the cylinder wall at mid-stroke position. The variation of fmep with viscosity provides a basis for comparing the effects of surface finish or piston design modifications. Using liners with fine honed bores reduced piston assembly friction by between 3 and 20 per cent relative to results for pistons running in plateau honed bores. Piston assembly friction was reduced by between 5 and 38 per cent through design changes to the pistons.

Burn angles and form factors for Wiebe function fits to mass fraction burned curves of a spark ignition engine with variable valve timing

Abstract The charge burn characteristics of a port-injected spark ignition engine with a pent-roof combustion chamber and variable valve timing have been investigated experimentally. The engine was run under stoichiometric mixture operating conditions over ranges of intake and exhaust valve timings, engine speed, and engine load. Empirical functions have been developed for the 0–90 per cent mass fraction burned angle and the form factor, which define Wiebe function fits to the mass fraction burned variation in the crank angle domain. The burn angle and form factor have been related to the level of charge dilution by burned gas, engine speed, ignition timing, and charge density at spark timing. The dilution level has the strongest influence on the burn rate and profile. The dilution level varied with intake and exhaust valve timings, external exhaust gas recirculation, and engine load. The results indicate that intake and exhaust valve timings influence combustion primarily by modifying the charge dilution with burned gas and charge density.

The effectiveness of stop-start and thermal management measures to improve fuel economy

Measures to reduce fuel consumption penalties associated with idling and cold engine operation have been have been investigated through experimental and computational simulation studies. The experimental work was carried out on a 1.6l, 4 cylinder SI engine. In cold-started New European Drive Cycle (NEDC) simulations of the engine in a B Class vehicle, stop-start strategies to eliminate idle fuel consumption was most effective, improving fuel economy by a predicted 7.7%. Minimising the time a switchable coolant pump was on saves up to 1% through reduced parasitic work. In warm up tests at constant speed and load, using a hot coolant store to reintroduce hot coolant on or before start-up reduced fuel consumption by 2.3% over 500s. Encapsulating the engine and power take off with thermal insulation slows cool-down from previous engine running and gives a higher restart temperature. Depending on the restart temperature, the fuel saving over the NEDC can be several per cent.

Investigations of fuel injection strategy for cold starting direct-injection diesel engines

Abstract The introduction of high-pressure common-rail fuel injection systems for diesel engines has given much greater electronic control over the patterns of fuel injection. Fuel delivery per cycle can be split into several small injections. The effect of the number, proportionate size and timing of these on work output per cycle and cycle-by-cycle variability under cold-start conditions has been investigated experimentally. High work output and low variability are consistent with short repeatable start times. Fuel per cycle has been delivered in one, two, or three injections. The injection timing and quantity of each part were varied. Cold tests were carried out at an engine soak temperature of −10 °C and engine speed was motored up to 300 r/min before enabling fuelling. The average gross indicated mean effective pressure (IMEP) of the first five fuelled engine cycles was recorded as the prime measure of quality. Splitting the injection into two parts maximizes the IMEP produced on firing cycles; a three-part split confers no additional advantage. The timing and separation of the injections strongly influence the probability that non-firing cycles occur and in turn this strongly influences average IMEP values.

Main bearing friction and thermal interaction during the early seconds of cold engine operation

Motoring tests have been carried out on an unloaded crankshaft to examine the friction levels in main bearings and the influence of local thermal conditions, at speeds covering the range of 200–1000 rev/min and initial temperatures down to −20°C. The temperatures of the bearing oil film and adjacent metal are strongly coupled. This strongly influences the variation of friction during the early seconds of running. The possibility of reducing the thermal mass which acts as a heat sink for heat transferred has been examined. Heat conduction through the bearing shells can be reduced by raising the contact resistance at the back surface of the shells. Experimental data and model predictions show a significant reduction in initial friction levels can be achieved.Copyright

The variation of in-Cylinder Mixture Ratios during Engine Cranking at Low Ambient Temperatures:

The development of mixture conditions in the cylinder of a fuel-injected spark ignition engine during engine cranking has been investigated at ambient temperatures down to —20°C. Mixtures near to the spark plug location were sampled and analysed to determine the air-fuel ratio and the relative proportions of light, medium and heavy components in the fuel. At low temperatures, the local air-fuel ratio varies substantially during the compression stroke, as does mixture composition. The change in mixture ratio over successive cycles of cranking depends on the fuel injected per cycle and the fuel-transfer characteristics of the intake port. The success or failure of combustion initiation is observed to depend only on the mixture air-fuel ratio at the spark plug. The upper limit on this mixture ratio for successful first-fire appears to be near to 35 : 1 by mass. Air-borne fuel in the cylinder accounts for only a small percentage of that supplied by the injector.

Factors influencing the burn rate characteristics of a spark ignition engine with variable valve timing

Abstract The charge burn characteristics of a four-cylinder port-fuel-injected spark ignition engine fitted with a dual independent variable-valve-timing system have been investigated experimentally. The influence of valve timings on the flame development angle and the rapid burn angle is primarily associated with valve overlap values and internal gas recirculation. Conditions examined cover light to medium loads and engine speeds up to 3500r/min. As engine loads and speeds exceeded about 6bar net indicated mean effective pressure and 3000r/min respectively, combustion duration was virtually independent of the valve timing setting. At lower speeds and work output conditions, valve timing influenced burn angles through changes in dilution mass fraction, charge density, and charge temperature. Of these, changes in dilution mass fraction had the greatest influence. Increasing the dilution by increasing the valve overlap produced an increase in both burn angles. The effects of mean piston speed and spark timing have also been examined, and empirical expressions for the flame development and the rapid burn angles are presented.

Experimental Data Processing Techniques to Map the Performance of a Spark Ignition Engine

Mapping the performance of an internal combustion engine over a wide range of operating conditions is a common procedure during development. The generation and post-processing of the data are high-cost activities. Two approaches which offer advantages over parametric test plans have been investigated. A statistically designed matrix of tests has been employed to map engine stability and combustion performance parameters. This approach minimizes the number of tests required and post-processing techniques provide valuable insight to relationships which exist between variables. This is particularly useful and efficient when qualitative trends are of prime interest. When large data sets are necessarily acquired and quantitative relationships between variables are of particular concern, then data processing using neural networks is shown to be an effective approach. The use of this technique is illustrated by application to evaluate relationships between engine-out emissions and engine state variables.