Ian Graham Pegg

‘Inlet suction’, a load support mechanism in non-convergent, pocketed, hydrodynamic bearings

Abstract It is shown that a simple parallel pad bearing containing a closed pocket can support load if it operates in an ambient pressure that is appreciably in excess of the cavitation pressure of the lubricating fluid. This arises due to fluid flow driven by subambient pressures in the inlet region of the pad (‘inlet suction’). Maximum load capacity occurs when the pocket is located near the inlet to the bearing and under conditions such that cavitation is just provoked.

Systems Approach to the Improvement of Engine Warm-Up Behaviour

Modifications to the coolant and oil circuits of a modern production 2.4 l diesel engine have been made in an attempt to promote oil warm-up to reduce fuel consumption. The new system used oil to cool exhaust gas recirculation (EGR) gases and incorporates a number of coolant flow control valves to reduce heat loss during warm-up. The engine was run over cold-start New European Drive Cycles with various flow strategies as a screening exercise to understand the behaviour of the system. Fuel consumption benefits of up to 4 per cent were observed, but these were accompanied by 3 per cent increases in nitrogen oxide (NO x ) emissions. Detailed analysis of the coolant flows and temperatures showed that, when throttling the flow, the mass of coolant in the degas bottle and radiator could be isolated from the system during warm-up, essentially reducing the thermal inertia. Heat transfer directly to the oil from the EGR gases rather than via the coolant allowed more heat to be put into the oil, with engine oil supply temperatures up to 6 °C hotter; however, it was not possible to verify that the oil was hotter at the bearings, valve train, and cylinder liner. The engine strategy was seen to react to the faster warm-up and to retard injection timing, reducing NO x but also compromising overall fuel consumption benefits. Further tests were conducted with various injection timings to establish a NO x —fuel consumption trade-off to demonstrate further benefits when the engine strategy is included in the operation of novel thermal management systems.

Cooling system improvements — assessing the effects on emissions and fuel economy

Abstract The work reported in this paper details an experimental study of the effects of cooling system hardware changes on diesel engine emissions and fuel economy. Experiments were performed under both steady state and transient conditions and complemented by statistical assessments. Techniques for assessing the thermal integrity of the engine as a consequence of such changes are also presented. An experimental design was constructed to investigate the effect of water pump throttling, coolant flow control through the oil cooler, and the adoption of a pressure resistive thermostat (PRT). Use of these thermal controls offers a useful trade-off between NO x and fuel economy, with a saving of around 3 per cent in b.s.f.c. for a 10 per cent NO x penalty at low load, where NO x output is less of a concern. However, these benefits were not observed during drive cycle testing.

Review of the systems analysis of interactions between the thermal, lubricant, and combustion processes of diesel engines

Abstract A review of technologies surrounding the thermal management system of the modern diesel engine with increased attention on fuel consumption is presented. A system-based approach has been adopted, looking at the interaction with other key systems. Previous innovation has aimed at reducing the power consumption of the cooling system or incorporating different cooling strategies and improving the engine warm-up rate for improved fuel consumption by higher operating temperatures. Electrical pumps can operate independently of the engine speed, and precision cooling and nucleate boiling have improved the heat transfer within the engine, reducing coolant flow requirements by 90 per cent. Improved warm-up rates have been demonstrated by using reduced thermal inertia or energy recovery systems either simulated on the test rig or through heat exchangers with exhaust gases. The resultant reduction in the fuel consumption is a result of various effects of the temperature on both the lubricating system and the combustion process. Despite difficulties in accurately measuring the engine friction, studies suggest that an increase in the engine temperature from 50°C to 80°C reduces the engine friction by 44 per cent because of 67 per cent lower oil viscosity. Simultaneous reduction in the emissions of nitogen oxides (NO x ) and the fuel consumption of 13.5 per cent and 0.7 per cent respectively have been achieved by including the engine thermal system in the calibration procedure. However, in-cylinder data needs to be studied to understand fully the mechanisms involved. Hotter engine temperatures reduce ignition delay, making combustion occur earlier in the cycle, which has a positive effect on the fuel consumption but a negative effect on the NO x emissions. Engine thermal management requires a system-based approach if the effects are to be fully understood but offers potential as an additional parameter in engine calibration.

Transient effects in lubricated textured bearings

The aim of this paper is to study the transient phenomena in hydrodynamic textured bearings. Both convergent and convergent–divergent reciprocating textured bearings are considered. A mass-conserving formulation of the Reynolds equation recently proposed by some of the authors and used to capture cavitation in steady-state lubricated contacts has been implemented to study transient effects in lubricated textured bearings. It is shown that the proposed solver is capable of capturing the frictional response of bearings characterised by various geometries and loading conditions in both steady-state and transient configurations. Depending on the boundary conditions governing the problems under investigation, changes in load support or film thickness variations are correctly predicted, demonstrating that the methodology developed in this paper is suitable to provide an efficient tool for the design and optimisation of textured bearings. A qualitative comparison with preliminary experimental data obtained using an apparatus developed to study reciprocating textured surfaces is performed, showing that the characteristic transient behaviour of such surfaces in different loading regimes can be correctly captured using the proposed numerical implementation.

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.

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.

The influence of cylinder deactivation on the emissions and fuel economy of a four-cylinder direct-injection diesel engine

The potential benefits and limitations of deactivating two of four cylinders by cam switching to disable the intake and exhaust valve lift were investigated experimentally on a turbocharged four-cylinder common-rail direct-injection diesel engine. When running on two firing cylinders, at light engine loads (a brake mean effective pressure of 2 bar, based on four-cylinder operation), the brake specific fuel consumption at given engine-out nitrogen oxide levels is comparable with or marginally better than when the engine is running on four cylinders. Cylinder deactivation allowed higher fuel rail pressures to be used to reduce the soot emissions while maintaining the advantages of lower carbon monoxide emissions and lower hydrocarbon emissions. At engine loads with a brake mean effective pressure of up to 3 bar on four cylinders, cylinder deactivation lowered the carbon monoxide and hydrocarbon emissions and raised the exhaust gas temperature by around 120 °C but, at higher loads, the fuel economy deteriorated and the soot and nitrogen oxide emissions increased markedly. The benefits of cylinder deactivation are therefore limited to light-load operating conditions, where the fuel economy is improved, the hydrocarbon and carbon monoxide emissions are reduced and the exhaust gas temperature is raised.

Systems optimisation of an active thermal management system during engine warm-up

Active thermal management systems offer a potential for small improvements in fuel consumption that will contribute to upcoming legislation on carbon dioxide emissions. These systems offer new degrees of freedom for engine calibration; however, their full potential will only be exploited if a systems approach to their calibration is adopted, in conjunction with other engine controls. In this work, a design-of-experiments approach is extended to allow its application to transient drive cycles performed on a dynamic test stand. Experimental precision is of crucial importance in this technique since even small errors would obscure the effects of interest. The dynamic behaviour of the engine was represented mathematically in a manner that enabled conventional steady state modelling approaches to be employed in order to predict the thermal state of critical parts of the engine as a function of the actuator settings. A 17-point test matrix was undertaken, and subsequent modelling and optimisation procedures indicated potential 2–3% fuel consumption benefits under iso-nitrogen oxide conditions. Reductions in the thermal inertia appeared to be the most effective approach for reducing the engine warm-up time, which translated approximately to a 1.3% reduction in the fuel consumption per kilogram of coolant. A novel oil-cooled exhaust gas recirculation system showed the significant benefits of cooling the exhaust gases, thereby reducing the inlet gas temperature by 5 °C and subsequently the nitrogen oxide emissions by 6%, in addition to increasing the warm-up rate of the oil. This suggested that optimising the thermal management system for cooling the gases in the exhaust gas recirculation system can offer significant improvements. For the first time this paper presents a technique that allows simple predictive models of the thermal state of the engine to be integrated into the calibration process in order to deliver the optimum benefit. In particular, it is shown how the effect of the thermal management system on the nitrogen oxides can be traded off, by advancing the injection timing, to give significant improvements in the fuel consumption.

The effect of engine and transmission oil viscometrics on vehicle fuel consumption

Abstract An extensive programme of work has been undertaken to assess the potential benefits of modulating the properties of both the engine and the transmission lubricating oils to achieve lower fuel consumption. The performance of the engine lubricants was evaluated on a production diesel engine on a transient test bed. The main engine lubricating-oil viscometric properties investigated were the cold cranking shear, the kinematic viscosity at 100°C, and the high-temperature high-shear value. Up to 3.5 per cent fuel economy improvement was observed over the New European Drive Cycle (NEDC), relative to current production lubricants. A model relating the fuel consumption to the oil properties was developed and verified using an experimental programme conducted on a chassis dynamometer. In a related study, the effects of changes in the transmission lubricant properties were evaluated using a standard five-speed manual transmission fitted to a light-goods vehicle and tested on a chassis dynamometer. The lubricant was heated using an external energy source to simulate the effect of a more rapid warm-up; this reduced the viscosity of the lubricant and a fuel consumption improvement of 0.7 per cent was demonstrated over the NEDC from a 25°C start. In addition, a lower-viscosity lubricant blend was evaluated, which delivered a 1 per cent improvement in the fuel economy over the standard blend from a cold start, and a further 0.4 per cent improvement if heated.