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 UK's 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

Turbulent flame and mass burning rate in a spark ignition engine

Turbulent burning rates were measured in an spark-ignition engine with extensive optical access for a fairly wide range of operating conditions. Skip-fired operation was employed to eliminate the effects caused by trapped or recirculated exhaust gases. Three main stages of turbulent flame propagation in SI engines were discerned: an initial acceleration, propagation with approximately constant speed and final deceleration caused by the proximity of walls. The rate of the initial flame acceleration showed little sensitivity to the engine operating parameters if the burning rate was expressed in terms of dimensionless flame radius. Propagation at a constant burning rate occurred over most of the charge volume but only for a minor fraction of its mass; the burning rate in this regime was proportional to the turbulence root-mean-square velocity while the influence of all other relevant factors could be encapsulated in either Karlovitz stretch factor or Damkohler number. The final stage of combustion, where the burnt gas radius was within one integral length scale from the walls, was responsible for more than two-thirds of the charge mass consumption and occurred at decreasing burning rate and flame brush thickness