The development of four-stroke, spark-ignition engines that are designed to inject gasoline directly into the combustion chamber is an important worldwide initiative of the automotive industry. The thermodynamic potential of such engines for significantly enhanced fuel economy, transient response and cold-start hydrocarbon emission levels has led to a large number of research and development projects that have the goal of understanding, developing and optimizing gasoline direct-injection (GDI) combustion systems. The processes of fuel injection, spray atomization and vaporization, charge cooling, mixture preparation and the control of in-cylinder air motion are all being actively researched, and this work is reviewed in detail and analyzed. The new technologies such as high-pressure, common-rail, gasoline injection systems and swirl-atomizing gasoline fuel injectors are discussed in detail, as these technologies, along with computer control capabilities, have enabled the current new examination of an old objective; the direct-injection, stratified-charge (DISC), gasoline engine. The prior work on DISC engines that is relevant to current GDI engine development is also reviewed and discussed.

The fuel economy and emission data for actual engine configurations are of significant importance to engine researchers and developers. These data have been obtained and assembled for all of the available GDI literature, and are reviewed and discussed in detail. The types of GDI engines are arranged in four classifications of decreasing complexity, and the advantages and disadvantages of each class are noted and explained. Emphasis is placed upon consensus trends and conclusions that are evident when taken as a whole. Thus the GDI researcher is informed regarding the degree to which engine volumetric efficiency and compression ratio can be increased under optimized conditions, and as to the extent to which unburned hydrocarbon (UBHC), NOx and particulate emissions can be minimized for specific combustion strategies. The critical area of GDI fuel injector deposits and the associated effect on spray geometry and engine performance degradation are reviewed, and important system guidelines for minimizing deposition rates and deposit effects are presented. The capabilities and limitations of emission control techniques and aftertreatment hardware are reviewed in depth, and areas of consensus on attaining European, Japanese and North American emission standards are compiled and discussed.

All known research, prototype and production GDI engines worldwide are reviewed as to performance, emissions and fuel economy advantages, and for areas requiring further development. The engine schematics, control diagrams and specifications are compiled, and the emission control strategies are illustrated and discussed. The influence of lean-NOx catalysts on the development of late-injection, stratified-charge GDI engines is reviewed, and the relative merits of lean-burn, homogeneous, direct-injection engines as an option requiring less control complexity are analyzed. All current information in the literature is used as the basis for discussing the future development of automotive GDI engines.

Automotive Spark-Ignited Direct-Injection Gasoline Engines

Biodiesel combustion, emissions and emission control

Behavior of a diesel injection system with biodiesel fuel

A free piston internal combustion (IC) engine operating on high compression ratio (CR) homogeneous charge compression ignition (HCCI) combustion is being developed by Sandia National Laboratories to significantly improve the thermal efficiency and exhaust emissions relative to conventional crankshaft-driven SI and Diesel engines. A two-stroke scavenging process recharges the engine and is key to realizing the efficiency and emissions potential of the device. To ensure that the engine’s performance goals can be achieved the scavenging system was configured using computational fluid dynamics (CFD), zero- and onedimensional modeling, and single step parametric variations. A wide range of design options was investigated including the use of loop, hybrid-loop and uniflow scavenging methods, different charge delivery options, and various operating schemes. Parameters such as the intake/exhaust port arrangement, valve lift/timing, charging pressure and piston frequency were varied. Operating schemes including a standard uniflow configuration, a low charging pressure option, a stratified scavenging geometry, and an over-expanded (Atkinson) cycle were studied. The computational results indicated that a stratified scavenging scheme employing a uniflow geometry, and supplied by a stable, low temperature/pressure charge will best optimize the efficiency and emissions characteristics of the engine. The operating CR can be maximized through substantial replacement of the burned charge, while short-circuiting emissions can be controlled by late fuel introduction. The in-cylinder flows are important to both NOx and short-circuiting emissions with inadequate mixing (and resulting temperature stratification) the predominant driver of NO production, and fuel penetration to the exhaust valve region the main cause of unburned hydrocarbon emissions.

Optimizing the Scavenging System for a Two-Stroke Cycle, Free Piston Engine for High Efficiency and Low Emissions: A Computational Approach

Predictive zero-dimensional combustion model for DI diesel engine feed-forward control

The topics covered in this book include direct ignition systems for spark ignition engines (direct injection as an element of the mixture formation concept, the physical possibilities of direct injection methods, the Mitsubishi method, the Common Rail method, the ZWICKAU Pressure Pulse system, the IFP method and the Orbital method) and direct injection systems for compression ignition engines (injection rate modulation, injection systems with speed dependent injection rate, injection systems with accumulated fuel high-pressure (Common Rail), injection systems with speed dependent pressure wave and variable flow passage, injection systems with speed dependent modulation of the pressure wave - the diesel pressure pulse system, and injection systems for alternative fuels (liquid gases)).

Direct Injection Systems for Spark-Ignition and Compression-Ignition Engines

Combined application of CFD modeling and pressure-based combustion diagnostics for the development of a low compression ratio high-performance diesel engine

Analysis Method for the Spray Characteristics of a GDI System with High Pressure Modulation

The hydrocarbon emission of a two-stroke engine can be partially decreased by scavenging improvement, but emission levels of a four-stroke engine can be achieved only by changing the mixture formation concept, specifically excluding the fuel from the scavenging process. Numerous research projects of gasoline direct injection – from liquid injection to air assisted systems – have been concentrated on two-stroke engines, determining the selection of the concepts which are suitable for series applications. This paper presents such a concept, based on the ram tuned injection: The system is characterized by a pressure modulation which can be adapted for an appropriate injection law, determining a suitable mixture formation for an engine with specific features. This electronically controlled injection system has been developed as a compact low cost unit for application to two-stroke engines with swept volumes of 50 cm3 and 125 cm3 which equip the two-wheeled vehicles. Going from the advantageous spray characteristics of the system, a new combustion chamber has been designed. The engine results show that the engine torque remains in all of the speed range at least at the same level as for the base engines equipped with carburetors, while the bsfc decreases generally 35...45%. But the most important result is the reduction of pollution – with 80...94% for the HC Emissions and 90% for the CO Emissions respectively. Complete paper available under: http://www.sae.org/servlets/productDetail?PROD_TYP= PAPER&PROD_CD=1999-01-1248

Cornel Stan

Papers

Direct Injection Systems for Spark-Ignition and Compression-Ignition Engines

Combined application of CFD modeling and pressure-based combustion diagnostics for the development of a low compression ratio high-performance diesel engine

Analysis Method for the Spray Characteristics of a GDI System with High Pressure Modulation

Development of a Direct Injection Concept for Two Wheelers Equipped with Two Stroke Engines

Numerical Analysis of the Performances of a Small Two-Stroke Engine with Direct Injection