Chris Brace

Ultra Boost for Economy: Extending the Limits of Extreme Engine Downsizing

The paper discusses the concept, design and final results from the ‘Ultra Boost for Economy’ collaborative project, which was part-funded by the Technology Strategy Board, the UKs innovation agency. The project comprised industry- and academia-wide expertise to demonstrate that it is possible to reduce engine capacity by 60% and still achieve the torque curve of a modern, large-capacity naturally-aspirated engine, while encompassing the attributes necessary to employ such a concept in premium vehicles. In addition to achieving the torque curve of the Jaguar Land Rover naturally-aspirated 5.0 litre V8 engine (which included generating 25 bar BMEP at 1000 rpm), the main project target was to show that such a downsized engine could, in itself, provide a major proportion of a route towards a 35% reduction in vehicle tailpipe CO2 on the New European Drive Cycle, together with some vehicle-based modifications and the assumption of stop-start technology being used instead of hybridization. In order to do this vehicle modelling was employed to set part-load operating points representative of a target vehicle and to provide weighting factors for those points. The engine was sized by using the fuel consumption improvement targets and a series of specification steps designed to ensure that the required full-load performance and driveability could be achieved. The engine was designed in parallel with 1-D modelling which helped to combine the various technology packages of the project, including the specification of an advanced charging system and the provision of the necessary variability in the valvetrain system. An advanced intake port was designed in order to ensure the necessary flow rate and the charge motion to provide fuel mixing and help suppress knock, and was subjected to a full transient CFD analysis. A new engine management system was provided which necessarily had to be capable of controlling many functions, including a supercharger engagement clutch and full bypass system, direct injection system, port-fuel injection system, separately-switchable cam profiles for the intake and exhaust valves and wide-range fast-acting camshaft phasing devices. Testing of the engine was split into two phases. The first usied a test bed Combustion Air Handling Unit to enable development of the combustion system without the complication of a new charging system being fitted to the engine. To set boundary conditions during this part of the programme, heavy reliance was placed on the 1-D simulation. The second phase tested the full engine. The ramifications of realizing the engine design from a V8 basis in terms of residual friction versus the fuel consumption results achieved are also discussed. The final improvement in vehicle fuel economy is demonstrated using a proprietary fuel consumption code, and is presented for the New European Drive Cycle, the FTP-75 cycle and a 120 km/h (75 mph) cruise condition.

Review of engine cooling technologies for modern engines

Abstract The performance of the conventional engine-cooling system has always been constrained by the passive nature of the system and the need to provide the required heat-rejection capability at high-power conditions. This leads to considerable losses in the cooling system at part-load conditions where vehicles operate most of the time. A set of design and operating features from advanced engine- cooling systems is reviewed and evaluated for their potential to provide improved engine protection while improving fuel efficiency and emissions output. Although these features demonstrate significant potential to improve engine performance, their full potential is limited by the need to balance between satisfying the engine-cooling requirement under all operating ambient conditions and the system effectiveness, as with any conventional engine-cooling system. The introduction of controllable elements allows limits to be placed on the operating envelope of the cooling system without restricting the benefits offered by adopting these features. The integration of split cooling and precision cooling with controllable elements has been identified as the most promising set of concepts to be adopted in a modern engine-cooling system.

Dynamic Behaviour of a High Speed Direct Injection Diesel Engine

Many Diesel engine development programs concentrate almost exclusively on steady state investigations to benchmark an engines performance. In reality, the inter-action of an engines sub-systems under transient evaluation is very different from that evident during steady state evaluation. The transient operation of a complete engine system is complex, and collecting test data is very demanding, requiring sophisticated facilities for both control and measurement. This paper highlights the essential characteristics of a Diesel engine when undertaking testbed transient manouevres. Results from simple transient sequences typical of on-road operation are presented. The tests demonstrate how transient behaviour of the engine deviates greatly from the steady state optimum settings used to control the engine. The operation of the EGR system and its interaction with other sub-systems, in particular VGT, has a significant effect on emissions, fuel consumption and driveability, highlighting the need for dynamic optimisation as an integrated system.

Integrated Cooling Systems for Passenger Vehicles

Electric coolant pumps for IC engines are under development by a number of suppliers. They offer packaging and flexibility benefits to vehicle manufacturers. Their full potential will not be realised, however, unless an integrated approach is taken to the entire cooling system. The paper describes such a system comprising an advanced electric pump with the necessary flow controls and a supervisory strategy running on an automotive microprocessor. The hardware and control strategy are described together with the simulation developed to allow its calibration and validation before fitting in a B/C class European passenger car. Simulation results are presented which show the system to be controllable and responsive to deliver optimum fuel consumption, emissions and driver comfort.

Development and Field Trial of a Driver Assistance System to Encourage Eco-Driving in Light Commercial Vehicle Fleets

Driver training schemes and eco-driving techniques can reduce fuel consumption by 10%, but their effectiveness depends on the willingness of drivers to change their behavior, and changes may be short lived. Onboard driver assistance systems have been proposed, which encourage driving style improvement. Such systems, when fitted in commercial vehicles, can assume some authority since uneconomical driving styles can be reported to a fleet manager. A driver assistance system has been developed and tried in the field with commercial vehicle drivers. The system aims to reduce fuel consumption by encouraging two behaviors: reduced rates of acceleration, and early upshifting through the gears. Visual feedback is reinforced with audible warnings when the driver makes uneconomical power demands of the engine. Field trials of the system were undertaken in the U.K. using 15 light commercial vehicles, driven by their professional drivers from a range of commercial applications. The trials consisted of two-week baseline data collection, which drivers were not aware of, followed by two weeks of data collection with the system being active. During the trials a total of 39 300 km of trip data were collected, which demonstrated fuel savings of up to 12% and average fuel savings of 7.6%.

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.

Increasing accuracy and repeatability of fuel consumption measurement in chassis dynamometer testing

Abstract The aim of this paper is to identify and investigate the effect of small changes in test conditions when quantifying fuel consumption. Twelve test set-up variables were identified and intentionally perturbed from a standard condition, including the effect of removing the power-assisted steering pump. Initially a design-of-experiments (DoE) approach was adopted and the results showed that most of the tested parameters had significant effects on fuel consumption. Most of these effects were greater than the effect of typical technology changes assessed on chassis dynamometer facilities. For example, an increase of 8.7 per cent in fuel consumption was observed following a 90min battery discharge from vehicle headlamps. Similarly an increase of 5.5 per cent was observed when the rig was run 3km/h faster over a drive cycle, and 2.6 per cent when using tyres deflated by 0.5 bar. As a consequence, statistical tolerancing was used to suggest typical tolerances for test rig set-up variables. For example it was recommended that the tyre pressure be controlled to within 0.1 bar and the test rig speed to 0.3km/h. Further investigations were conducted into the effect of battery discharge, coast-down time, and engine cooling. These highlighted the need for rigorous battery charge management as the battery voltage was found not to be an appropriate measure of the variation in the alternator loading. Coast-down time was found to be a good control measure for a number of set-up variables affecting the rolling resistance of the vehicle. Finally the variations in the engine cooling were quantified using a cumulative engine temperature over a drive cycle. This was found to correlate well with fuel consumption. For each of these subsequent investigations, results were compared with the DoE predictions and found to agree well when considering the relatively low number of tests compared with the number of factors.

The potential for simulation of driveability of CVT vehicles

This paper introduces the work ongoing at the University of Bath in a series of projects aimed at characterising the driveability of CVT equipped vehicles and using the findings to help develop a strategy for a prototype powertrain controller during transient driving situations. Results of the driveability investigation of a first project in this series have already been published [1], where the driveability of three CVT vehicles was appraised. A follow-up project extends this work appraising more CVT vehicles and also comparing driveability aspects of CVT transmissions to conventional AT. The paper relates the common experimental part of the two projects showing linked results and describing how a simulation program can be used to predict and improve the driveability of the powertrain controller.