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Homogeneous Charge Compression Ignition (HCCI) engines offer high fuel efficiency and some emissions benefits. However, it is difficult to control and stabilize combustion over a sufficient operating range because the critical compression ratio and intake temperature at which HCCI combustion can be achieved varies with operating conditions such as speed and load as well as with fuel octane number. Replacing part of the base fuel with reformer gas, (which can be produced from the base hydrocarbon fuel), alters HCCI combustion characteristics in varying ways depending on the replacement fraction and the base fuel auto-ignition characteristics. Injecting a blend of reformer gas and base fuel offers a potential HCCI combustion control mechanism because fuel injection quantities and ratios can be altered on a cycle-by-cycle basis.

Homogeneous Charge Compression Ignition (HCCI) combustion offers high fuel efficiency and some emissions benefits. However, it is difficult to control and stabilize combustion over a significant operating range because the critical compression ratio and intake temperature at which HCCI combustion can be achieved vary with operating conditions such as speed and load as well as with fuel octane number. Replacing part of the base fuel with reformer gas, (which can be produced from the base hydrocarbon fuel), alters HCCI combustion characteristics in varying ways depending on the replacement fraction and the base fuel auto-ignition characteristics. Because fuel injection quantities and ratios can be altered on a cycle-by-cycle basis during operation, injecting a variable blend of reformer gas and base fuel offers a potential HCCI combustion control mechanism.

Combustion in Homogeneous Charge Compression Ignition (HCCI) engines is the subject of intensive combustion modeling efforts because, while they have potential for low fuel consumption and emissions, they also suffer from problems of combustion control. Modeling studies are being used to predict the effects of changing controllable parameters and to ‘measure’ important combustion-related phenomena which can not be observed directly. A significant limitation of most current combustion models is that they still rely on arbitrarily adjusting initial conditions, (especially temperature) in order to match experimental results. This limits the confidence with which models can be used to predict HCCI combustion behavior over any range of conditions wider than available experimental data. This paper describes a new method to solve the initial condition problems for HCCI combustion modeling based on simulated heat transfer between intake and residual components.

Despite progressive implementation of stringent emission regulations, vehicle tailpipe emissions remain the major source of air pollution problems in most urban areas. To control and reduce tailpipe pollutants, it is critical to understand in-use emissions as a basis for any future emission controls. At present, emission factors are mainly studied by chassis dynamometer methods. However, concerns have been raised about the extent to which emissions produced by on-road vehicles can be predicted using emission factors developed based on standardized dynamometer test procedures. This paper describes an on-board, in-use vehicle emissions measurement system which measures tailpipe emission rates while the vehicle is in real service experiencing complex traffic conditions, driver behavior and weather.

Motorized transport has become an essential part of our world economic system with an ever-increasing number of vehicles on the road. However, considering the depletion of energy resources and the aggravation of greenhouse gas issues, it is critical to improve vehicle fuel consumption. These demands are moving us toward advanced engine and powertrain technologies. However, understanding our progress also requires improvements in the way we measure and certify vehicle emissions and fuel economy performance. This paper describes the use of an on-board fuel consumption and emissions measurement system to develop on-road fuel consumption functions that can be used to quantify the fuel economy impact of vehicle, road and traffic control changes. The system uses an ECM OBD-II scanner, a Mass Air Flow meter and an emissions analyzer to monitor fuel consumption and exhaust CO2 emission rates (in g/s) as well as vehicle speed and other parameters.

At certain operating conditions, Homogeneous Charge Compression Ignition (HCCI) can provide ultra-low NOx emissions with good combustion efficiency. However, using HCCI operating modes in a SI-based engine still requires some means to control HCCI ignition over a range of operating conditions. Amongst various possible control techniques, altering fuel ignition quality by blending a reformer gas mixture with base fuel is attractive, primarily because of the capability to alter fuel injection ratios on a cycle-by-cycle basis. As well as fuel blending, the mixture composition is defined by equivalence ratio (ϕ) and exhaust gas recirculation (EGR) ratio. The effects of changing such parameters have been widely studied both experimentally and with models. However, adjusting any variable has multiple effects on the mixture's thermodynamic and chemical properties so a detailed understanding of how these variables affect combustion is generally difficult to achieve.

Because of the potential for low NOx emissions with high efficiency, HCCI engines could develop a significant niche in the engine world. However, HCCI engines suffer from a narrow operating range between knock and misfire boundaries because the ignition timing is only controlled by mixture chemistry and compression conditions. Varying combinations of operating parameters are required to obtain good combustion under different conditions and chemical kinetic models are widely used as an engine research tool. The performance of such models depends critically on the accuracy of the chemical mechanisms which are still under development and require some optimization, particularly for larger hydrocarbon molecules. This study starts with a Chalmers University mechanism [1] which is well-proven for pure n-heptane but works less well for mixtures blended with significant amounts of reformer gas containing high fractions of H2 and CO [2].

Although HCCI engines promise low NOx emissions with high efficiency, they suffer from a narrow operating range between knock and misfire because they lack a direct means of controlling combustion timing. A series of previous studies showed that reformer gas, (RG, defined as a mixture of light gases dominated by hydrogen and carbon monoxide), can be used to control combustion timing without changing mixture dilution, (λ or EGR) which control engine load. The effect of RG blending on combustion timing was found to be mainly related to the difference in auto-ignition characteristics between the RG and base fuel. The practical effectiveness of RG depends on local production using a fuel processor that consumes the same base fuel as the engine and efficiently produces high-hydrogen RG as a blending additive.