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Gasoline Homogeneous Charge Compression Ignition (HCCI) combustion has been studied widely in the past decade. However, in HCCI engines using negative valve overlap (NVO), there is still uncertainty as to whether the effect of pilot injection during NVO on the start of combustion is primarily due to heat release of the pilot fuel during NVO or whether it is due to pilot fuel reformation. This paper presents data taken on a 4-cylinder gasoline direct injection, spark ignition/HCCI engine with a dual cam system, capable of recompressing residual gas. Engine in-cylinder samples are extracted at various points during the engine cycle through a high-speed sampling system and directly analysed with a gas chromatograph and flame ionisation detector. Engine parameter sweeps are performed for different pilot injection timings and quantities at a medium load point.

The European Emissions Stage 5b standard for diesel passenger cars regulates particulate matter to 0.0045 g/km and non-volatile part/km greater than 23 nm size to 6.0x10₁₁ as determined by the PMP procedure that uses a heated evaporation tube to remove semi-volatile material. Measurement artifacts associated with the evaporation tube technique prevents reliable extension of the method to a lower size range. Catalytic stripper (CS) technology removes possible sources of these artifacts by effectively removing all hydrocarbons and sulfuric acid in the gas phase in order to avoid any chemical reactions or re-nucleation that may cause measurement complications. The performance of a miniature CS was evaluated and experimental results showed solid particle penetration was 50% at 10.5 nm. The sulfate storage capacity integrated into the CS enabled it to chemically remove sulfuric acid vapor rather than rely on dilution to prevent nucleation.

The gas velocity through an automotive catalyst has been determined by measuring the time of flight of a pulse of propane injected at the inlet plane of the catalyst. The arrival time at the exit plane was detected by a fast flame ionization detector. By synchronizing and delaying the injection of propane with respect to the engine crankshaft position, the fluctuations of the exhaust gas velocity during the engine cycle were investigated. A number of tests at different engine load and speed points were carried out. The results show a complex velocity/time characteristic, including flow reversals. The technique is shown to be a viable option for flow measurement in this harsh environment.

A novel modeling approach is applied to investigate the use of hydrogen-rich gas (HRG) for controlling the combustion process in a Homogenous-Charge Compression-Ignition (HCCI) engine. A detailed-chemistry stochastic reactor model is coupled with a one-dimensional gas dynamics model to account for the full engine cycle. The integrated model simulates the steady-state and transient operation of a single-cylinder HCCI engine. A previously developed tabulation scheme is utilized to speed up the detailed-chemistry simulations, which, though computationally cheap compared to many other approaches, are impractical for simulations involving a large number of cycles. A control strategy based on HRG addition is implemented using a closed-loop controller built within the gas dynamics model. Simulations conducted at different speeds and with varying loads indicate that the HRG can be effectively used to control the combustion phasing, and hence expand the operating range of the HCCI engine.

This paper describes cyclic Air/Fuel ratio (AFR) measurements carried out with a novel device (fUEGO) based on a production Universal Exhaust Gas Oxygen sensor, but modified to give an improved frequency response. The results are compared to AFR calculated from a fast CO/CO2 analyser and a fast response flame ionization detector (FID). The direct comparison of the two different methods for determining the cyclic AFR reveals that the electrochemical device is in reasonable agreement with the more complex carbon balance method and can provide reliable cyclic AFR measurements with a reduced requirement for equipment and data post processing. The fUEGO however is sensitive to elevated levels of uHC's (unburned hydrocarbons) during misfires or partial burns and readings during such situations usually show deviations compared to the carbon balance method.

A turbulent combustion model is described for SI engines with large variations in mixture strength. The model is for a single gas phase fluid at high Reynolds number and treats combustion in the laminar flamelet regime, which is characterized by high Damkholer and low Karlovitz numbers. An assumed probability density function (pdf) approach is used to extract expressions for mean quantities of interest, which are parameterized on the progress variable and mixture fraction variables. A double delta function pdf is used for the reaction progress variable and a beta function pdf is used for the mixture fraction. The reaction rate term in the progress variable equation is closed using an algebraic expression, which incorporates the effects of mixture strength, pressure and temperature on laminar flame speed. The model is implemented in two versions of a Computational Fluid Dynamics (CFD) code.