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This investigation was aimed at measuring the relative performance of two spray-guided, single-cylinder, spark-ignited direct-injected (SIDI) engine combustion system designs. The first utilizes an outwardly-opening poppet, piezo-actuated injector, and the second a conventional, solenoid operated, inwardly-opening multi-hole injector. The single-cylinder engine tests were limited to steady state, warmed-up conditions. The comparison showed that these two spray-guided combustion systems with two very different sprays had surprisingly close results and only differed in some details. Combustion stability and smoke emissions of the systems are comparable to each other over most of the load range. Over a simulated Federal Test Procedure (FTP) cycle, the multi-hole system had 15% lower hydrocarbon and 18% lower carbon monoxide emissions.

High-speed (12 kHz) imaging of combustion luminosity (enhanced by using a sodium fuel additive) has been analyzed and compared to crank angle resolved heat release rates and mass fraction burn profiles in a spray-guided spark-ignited direct-injection (SG-SIDI) optical single-cylinder engine. The addition of a sodium-containing additive to gasoline greatly increases the combustion luminosity, which allows unintensified high-speed (12 kHz) imaging of early partially premixed flame kernel growth and overall flame propagation with excellent signal-to-noise ratio for hundreds of consecutive engine cycles. Ignition and early flame kernel growth are known to be key to understanding and eliminating poor burn cycles in SG-SIDI engines.

A numerical and corresponding experimental study was undertaken to identify the ability to accurately predict combustion performance using our 3-D numerical tools for a direct-injection homogeneous-charge engine. To achieve a significant range of combustion rates, the evaluation was conducted for the engine operating with and without enhanced charge motion. Five charge motion configurations were examined, each having different levels of swirl and tumble flow leading to different turbulence generation and decay characteristics. A detailed CFD analysis provides insight into the in-cylinder flow requirements as well as the accuracy of the submodels. The in-cylinder air-fuel distribution, the mass-averaged swirl and tumble levels along with mean flow and turbulent kinetic energies are calculated throughout the induction and compression processes.

Recently, high-speed optical imaging data for a single operating point of a spray-guided gasoline engine has, along with the flamelet model and the G-equation theory, enabled the development of the new spark-ignition model SparkCIMM. Within its framework, detailed chemistry flamelet models capture the experimental feature of multiple localized ignition events along the excessively stretched and restriking spark channel, as well as the observations of non-spherical highly corrugated early turbulent flame fronts. The developed flamelet models account for the substantial turbulent fluctuations in equivalence ratio and enthalpy present under spray-guided conditions. A non-unity Lewis number formulation captures the deficient species diffusion into the highly curved flame reaction zone.

A CFD code is enhanced with a fuel tracer diagnostic to track the liquid and vapor fuel mass separately from individual spray plumes of a multi-hole injector and the wall film. The approach works by solving a set of additional scalar transport equations for fuel vapor generated from individual nozzle hole and the wall film. The diagnostic tool is first validated against experiments from a 4-valve, wall-guided spark-ignition direct-injection (SIDI) engine. A CFD analysis is carried out to understand the experimentally observed trade-offs in combustion stability and smoke emissions between a 70degree hollow-cone swirl injector and a 40 degree, 5-hole, circular-type multi-hole injector at a lean, stratified idle operating condition. Engine tests show that the multi-hole injector results in lower COV of IMEP than the hollow-cone swirl injector at the expense of significantly higher smoke emissions.

As vehicle fuel economy requirements continue to increase it is becoming more challenging and expensive to simultaneously improve fuel consumption and meet emissions regulations. The Passive Ammonia SCR System (PASS) is a novel aftertreatment concept which has the potential to address NOx emissions with application to both lean SI and stoichiometric SI engines. PASS relies on an underfloor (U/F) SCR for storage of ammonia which is generated by the close-coupled (CC) TWCs. For lean SI engines, it is required to operate with occasional rich pulses in order to generate the ammonia, while for stoichiometric application ammonia is passively generated through the toggling of air/fuel ratio. PASS serves as an efficient and cost-effective enhancement to standard aftertreatment systems. For this study, the PASS concept was demonstrated first using lab reactor results which highlight the oxygen tolerance and temperature requirements of the SCR.

Mean Value Engine Models, commonly used for model based fault diagnosis of SI engines, fail to capture the within-cycle dynamics of engines, often resulting in reduced fault sensitivity. This paper presents a new Hybrid Automata based modeling approach for characterizing the within-cycle dynamics of the thermo-fluidic processes in a Spark Ignition Gasoline Engine, targeted for use in model based fault diagnosis. Further, using a hybrid version of the Extended Kalman Filter (EKF), the states from the nonlinear hybrid automata based dynamic model are estimated and their results validated w.r.t standard industrial simulation software, AMESim. It is observed that due to the switching of within cycle engine dynamics, causing mode change, there is a corresponding change in model's structure which in turn can cause change in system's observability.

This study investigates a novel approach towards boosted HCCI operation, which makes use of all engine system components in order to maximize overall efficiency. Four-cylinder boosted HCCI engines have been modeled employing valve strategies and turbomachines that enable high load operation with significant efficiency benefits. A commercially available engine simulation software, coupled to the University of Michigan HCCI combustion and heat transfer correlations, was used to model the HCCI engines with three different boosting configurations: turbocharging, variable geometry turbocharging and combined supercharging with turbocharging. The valve strategy features switching from low-lift Negative Valve Overlap (NVO) to high-lift Positive Valve Overlap (PVO) at medium loads. The new operating approach indicates that heating of the charge from external compression is more efficient than heating by residual gas retention strategies.