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A major effort has been made to surmount the current obstacles to expanding the operating window of homogeneous charge compression ignition (HCCI) engines. The research involves extensive experimental studies on single-cylinder and multi-cylinder engines and the work is devoted to the development of on-board fuel-reforming technology and to the application of supercharging combined with trapping of residual gases in the cylinder. Fuel reforming yields significant quantities of hydrogen and is used to extend the lower load boundary while supercharging and internal exhaust gas recirculation (EGR) trapping are used to increase the upper load limit of HCCI engines. The present paper highlights the main findings of the research to date; in particular it reveals that using a combination of technical elements for effective control of auto-ignition in a typical passenger car engine configuration is possible and promising.

One of the most widely used methods to enable Homogeneous Charge Compression Ignition (HCCI) combustion is using negative valve overlapping to trap a sufficient quantity of hot residual gas. The characteristics of air motion with specially designed valve events having reduced valve lift and durations associated with HCCI engines and their effect on subsequent combustion are not yet fully understood. In addition, the ignition process and combustion development in such engines are very different from those in conventional spark-ignition or diesel compression ignition engines. Very little data has been reported concerning optical diagnostics of the flow and combustion in the engine using negative valve overlapping. This paper presents an experimental investigation into the in-cylinder flow characteristics and combustion development in an optical engine operating in HCCI combustion mode. PIV measurements have been taken under motored engine conditions to provide a quantitative flow characterisation of negative valve overlap in-cylinder flows. The ignition and combustion process was imaged using a high resolution charge coupled device (CCD) camera and the combustion imaging data was supplemented by simultaneously recorded in-cylinder pressure data which assisted the analysis of the images. It is found that the flow characteristics with negative valve overlapping are less stable and more valve event driven than typical spark ignition in-cylinder flows, while the combustion initiation locations are not uniformly distributed. © 2006 IOP Publishing Ltd.

The desire to minimise fuel consumption and corresponding vehicle CO 2 emissions for future powertrain applications drives the need for advanced charging systems. Worldwide legislative requirements and customer desires for improved efficiency whilst maintaining vehicle drivability and performance are challenging automotive manufacturers to investigate innovative concepts for air charge delivery.

While Homogeneous Charge Compression Ignition (HCCI) is a promising combustion mode with significant advantages in fuel economy improvement and emission reductions for vehicle engines, it is subject to a number of limitations, for example, hardware and control complexity, or NOx and NVH deterioration near its operating upper load boundary, diminishing its advantages. Conventional spark-ignition combustion mode is required for higher loads and speeds, thus the operating conditions near the HCCI boundaries and their corresponding alternatives in Sl mode must be studied carefully in order to identify practical strategies to minimise the impact of the combustion mode transition on the performance of the engine. This paper presents the results of an investigation of the combustion mode transitions between Sl and HCCI, using a combination of an engine cycle simulation code with a chemical kinetics based HCCI combustion code. It investigates and discusses the key issues concerning the combustion mode transition and its control. A new approach has been adopted in the modelling of the HCCI engine gas exchange and combustion, which allowed a parametric study of the transient process in the transition on a cycle-by-cycle basis and provided guidelines in the design of the engine hardware and its control strategies.

A single zone combustion model based on a chemical kinetic solver has been combined with a one-dimension thermo/gas dynamic engine simulation code to study the operating characteristics of a V6 engine In which Homogeneous Charge Compression Ignition (HCCI) operation (also referred to as 'Controlled Auto-ignition" CAI) is enabled by a cam profile switching (CPS) system with negative valve overlap. An operational window within which HCCI combustion is possible has been identified and the limit of HCCI operating region for varied valve lift possibilities is explored. The mechanisms and potential fuel economy improvements within the HCCI envelope are studied and modelled results compared against data from similar engines. It is shown that for the best fuel economy the valve timing strategy needs to be selected very carefully, despite the engine's capability to operate at a range of valve timing combinations. The heating effect of the exhaust gases is dominant when using less than approximately 55% residual gases. For higher EGR rates, the diluting effect coupled with reducing exhaust gas temperatures makes the ignition timing retarded. It is demonstrated that for HCCI operation the selection of valve lift for the CPS system is limited between the constraints of the breathing capacity with the lower valve lift and misfires with the higher one.

The Ultraboost project outlined in this paper seeks to develop a highly pressure-charged, downsized, spark ignition engine that is capable of a 35% reduction in tailpipe CO 2 emissions over a naturally aspirated 5.0 L V8 while still maintaining performance, emissions and transient response. This project is especially ambitious since, in order to achieve this level of fuel economy improvement, a 60% reduction in engine displacement is targeted with a BMEP of greater than 30 bar. What is more, achieving these targets in a gasoline engine with stoichiometric fuelling requires careful design and component selection in order to address the many challenges surrounding gasoline combustion under such high boost pressures. This paper describes a critical examination of the competing requirements of a heavily downsized, gasoline engine with a specific focus on the role of the boosting system in delivering these requirements. From this analysis, the optimal base boosting system configuration is investigated. In addition, a number of boosting technologies, ranging from the novel to the more traditional, are discussed in view of their ability to fulfil a role on the Ultraboost engine. A set of assessment criteria is presented in order to facilitate the selection process. Finally, a 1-D GT-Power model of the Ultraboost engine equipped with the different boosting systems was used to generate an informed rating of all boosting options and permit a reliable comparison with respect to the targets of the project.