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Advances in Internal Combustion Engines (ICE) deal with a multitude of combustion properties, such as combustion efficiency, emissions and quality. However, not only the combustion needs refinement in a modern engine, also parasitic losses have to be minimized. All of them are addressed in the two recently released Saab concepts, Saab Variable Compression (SVC) [1] and Saab Combustion Control (SCC) [2]. The strongest motivator for their specific designs is the desire to improve fuel economy. Both systems are briefly presented in this paper and the respective concepts are thoroughly discussed with respect to the above mentioned combustion characteristics and parasitic losses.

During development of an air assisted, direct injection combustion system, it was found that an air pulse during the late part of compression stroke significantly shortened the combustion duration and extended the lean limits of the engine. The effect of an injection of pure air through an air assist direct injector was studied with Particle Image Velocimetry, PIV. Results showed that an air pulse during the compression stroke significantly speeded up in-cylinder velocities, which also was showed in the heat release analysis. A system to use low density seeding particles was developed and is presented in the paper.

Continuously Variable Cam Phasers (CVCP) controlling both the exhaust and intake camshaft phasing in combination with air assist direct fuel injection and a wide variable spark gap is utilized to reduce the fuel consumption for a 4-valve Turbo Charged (TC) Spark Ignition (SI) engine. The spark plug and the air-assisted direct fuel injector are integrated into one unit in order to facilitate packaging in a modern 4-valve combustion chamber. This integrated component is referred to as the Spark Plug Injector (SPI). CVCP's are used to reduce pumping work by diluting the charge with large amounts of residual exhaust gas. This strategy, along with stoichiometric homogeneous operation enables the use of a Three Way Catalyst (TWC), considered to be a prerequisite to meet the emission standards of Ultra Low Emission Vehicles (ULEV) II and beyond. The ignition quality deteriorates with increasing levels of residual exhaust gas dilution.

This paper presents a study of the Spark To Piston (STP) concept, engaged in a modern Spark Ignition (SI) 4-valve per cylinder four stroke engine. The combustion stabilization effect from this concept has been utilized in order to increase the engine tolerance to dilution of the fresh air-fuel mixture. It is shown that this tolerance is significantly improved by the STP concept, especially if combined with a high-energy ignition system. Inherent with this improved tolerance comes the ability to reduce fuel consumption and emissions of NOx in a considerable amount. Consequently, STP must therefore be considered a competitive future technique despite its non-conventional approach.

The work presented in this paper addresses the effects on combustion of recycling cooled exhaust gas (EGR) to the inlet charge of a standard production, four cylinder 2.3 l turbocharged, SI engine. The effect of various amounts of EGR at different temperatures and ignition timings were investigated. Considerable knock suppression at power output comparable with what was achieved with fuel enrichment, could be achieved by adding cooled EGR. Due to inherent high thermal loads, turbocharged engines have been operated at rich air/fuel-ratios during high load conditions, with subsequent high tailpipe emissions of CO in particular, but also HC. By substituting fuel enrichment with cooled EGR, a stoichiometric charge can be used, thus enabling the use of a three way catalytic converter at all operating conditions.