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Results from a large set of HCCI experiments performed on a single-cylinder research engine fueled with different mixtures of iso-octane and n-heptane are presented and discussed in this paper. The experiments are designed to scrutinize fuel reactivity effects on the operating range of an HCCI engine. The fuel effects on upper and lower operating limits are measured respectively by the maximum pressure rise rate inside the cylinder and the stability of engine operation as determined by cycle-to-cycle variations in IMEP. Another set of experiments that examine the intake air heating effects on HCCI engine performance, exhaust emissions and operating envelopes is also presented. The effects of fuel reactivity and intake air heating on the HCCI ranges are demonstrated by constructing the operating envelopes for the different test fuels and intake temperatures.

We numerically simulate a Homogeneous Charge Compression Ignition (HCCI) engine fuelled with a blend of ethanol and diethyl ether by means of a stochastic reactor model (SRM). A 1D CFD code is employed to calculate gas flow through the engine, whilst the SRM accounts for combustion and convective heat transfer. The results of our simulations are compared to experimental measurements obtained using a Caterpillar CAT3401 single-cylinder Diesel engine modified for HCCI operation. We consider emissions of CO, CO2 and unburnt hydrocarbons as functions of the crank angle at 50% heat release. In addition, we establish the dependence of ignition timing, combustion duration, and emissions on the mixture ratio of the two fuel components. Good qualitative agreement is found between our computations and the available experimental data.

This paper describes a novel catalytic oxidation sensor which represents an attempt to realise a practical sensor for on vehicle detection of catalyst efficiency and misfire. Via experimental and modelling approaches, promising characteristics are established, which could mean that an application to the on-vehicle detection of catalyst efficiency and misfire is feasible.

Flamelet modelling of premixed turbulent combustion can be applied to spark-ignition engine combustion. To address and validate several modelling criteria, two measurement techniques are used in a burner flame to study the interaction between turbulent flowfields and combustion for subsequent application to engine combustion. Particle Image Velocimetry and Light Sheet Tomography are used together to measure conditional velocities simultaneously in reactant and product mixtures. Correlations of velocity and reaction scalar fluctuations indicate that counter-gradient turbulent diffusion must be accounted for when modelling this flowfield. Comparisons of spatial averaging of instantaneous and ensemble-averaged data are made and the application of similar techniques to engine combustion is discussed.

An experimental study of the use of air-reformed natural gas (natural gas broken down into hydrogen and carbon monoxide) in a spark-ignited engine was performed. Results measured included work output, brake efficiency, and the output of NOX) CO and total hydrocarbons. The principle variables were the equivalence ratio and the fraction of fuel reformed. The hydrogen in the reformed fuel allowed the engine to run leaner than when running on natural gas, especially when higher fractions of reformed fuel were used. At the leaner equivalence ratios low levels of NOx were observed, with NOx mole fractions frequently below 10 ppm. Carbon monoxide and hydrocarbons were generally reduced by the reformed fuel. Efficiencies were higher with reformed fuel in some ranges of operation, and about the same in other ranges of operation.

Cooled exhaust gas recirculation (EGR) is widely used in diesel engines to control engine-out NOx (oxides of nitrogen) emissions. A portion of the exhaust gases is re-circulated into the intake manifold of the engine after cooling it through a heat exchanger. EGR cooler heat exchangers, however, tend to lose efficiency and have increased pressure drop as deposit forms on the heat exchanger surface due to transport of soot particles and condensing species to the cooler walls. In this study, condensation of water vapor and hydrocarbons at the exit of the EGR cooler was visualized using a fiberscope coupled to a camera equipped with a complementary metal oxide semiconductor (CMOS) color sensor. A multi-cylinder diesel engine was used to produce a range of engine-out hydrocarbon concentrations. Both surface and bulk gas condensation were observed with the visualization setup over a range of EGR cooler coolant temperatures.

The performance of ammonia as a fuel for gas turbine application has been theoretically predicted. Regenerative and nonregenerative Brayton cycles were employed as theoretical models, and combustion products were treated as a chemical equilibrium reactive system. All calculations were carried out by programs developed for use on an IBM 7094 digital computer. The results indicate that ammonia should be superior to hydrocarbons as a fuel on the basis of output and efficiency, but poorer on the basis of fuel economy.

Using a novel, high frequency response FID unit, hydrocarbon measurements in the spark plug gap of a firing gasoline engine have been made. These measurements have been correlated with the pressure development, and a significant correlation was found. The method described can be used on any engine fitted with a modified sparking plug.

A square-piston engine simulator used at Berkeley to study both spark-ignited and diesel engine processes is described. The square piston configuration provides optical access to fluid mechanical and combustion processes through two fiat quartz windows used as cylinder walls. Results from three previous research projects are reviewed to illustrate the engine's capabilities. Since these studies, we developed and used a color schlieren cinematography system to record in-cylinder processes. Color schlieren movies of both spark-ignition and diesel combustion reveal the essential fluid mechanical and combustion features within the engine. For these movies, we redesigned the diesel fuel system and installed a new liquid fuel injection system for spark-ignited operation. By preventing fuel and soot condensation on the windows, these new fuel systems improved the quality of our Schlieren images.

Experiments were performed to measure the number-weighted particle size distributions emitted from a gasoline direct injection (GDI) engine. Measurements were made on a late model vehicle equipped with a direct injection spark ignition engine. The vehicle was placed on a chassis dynamometer, which was used to load the engine to road load at five different vehicle speeds ranging from 15 - 100 km/hr. Dilution of the exhaust aerosol was carried out using a two-stage dilution system in which the first stage dilution occurs as a free jet. Particle size distributions were measured using a TSI 3934 scanning mobility particle sizer. Generally speaking, the presence of the additives did not have a strong, consistent influence on the particle emissions from this engine. The polyether amine demonstrated a reduction in particle number concentration as compared to unadditized base fuel.

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.

A fast response sensor for measuring carbon dioxide concentration has been developed for laboratory research and tested on a spark ignition engine. The sensor uses the well known infra-red absorption technique with a miniaturized detection system and short capillary sampling tubes, giving a time constant of approximately 5 milliseconds; this is sufficiently fast to observe changes in CO2 levels on a cycle-by-cycle basis under normal operating conditions. The sensor is easily located in the exhaust system and operates continuously. The sensor was tested on a standard production four cylinder spark-ignition engine to observe changes in CO2 concentration in exhaust gas under steady state and transient operating conditions. The processed sensor signal was compared to a standard air-to-fuel ratio (AFR) sensor in the exhaust stream and the results are presented here. The high frequency response CO2 measurements give new insights into both engine and catalyst transient operation.

Experiments were performed to measure the average and time-resolved particle number emissions and number-weighted particle size distributions from a gasoline direct injection (GDI) engine. Measurements were made on a late model vehicle equipped with a direct injection spark ignition engine. The vehicle was placed on a chassis dynamometer, which was used to load the engine to road load at five different vehicle speeds ranging from 13 - 90 km/hr. Particle number emissions were measured using a TSI 3020 condensation nucleus counter, and size distributions were measured using a TSI 3934 scanning mobility particle sizer. Average polydisperse number concentration was found to increase from 1.1 × 108 particles/cm3 at 13 km/hr to 2.8 × 108 particles/cm3 at 70 km/hr. Under a closed-loop, stoichiometric homogeneous charge operating mode at 90 km/hr, number emissions fell to 9.3 × 107 particles/cm3 (at all other operating conditions, the engine was in a lean stratified charge operating mode).

In recent years magnetic resonance imaging (MRI) has been shown to be an attractive method for fluid flow visualization. In this work, we show how MRI velocimetry techniques can be used to non-invasively investigate and visualize the hydrodynamics of exhaust gas in a diesel particulate filter (DPF), both when clean and after loading with diesel engine exhaust particulate matter. The measurements have been used to directly measure the gas flow in the inlet and outlet channels of the DPF, both axial profiles along the length and profiles across the channel diameter. Further, from this information we show that it is possible to indirectly ascertain the superficial wall-flow gas velocity and the soot loading profiles along the filter channel length.

Three-dimensional Computational Fluid Dynamics (CFD) has become an integral part in analysing engine in-cylinder processes since it provides detailed information on the flow and combustion, which helps to find design improvements during the development of modern engine concepts. The predictive capability of simulation tools depends largely on the accuracy, fidelity and robustness of the various models used, in particular concerning turbulence and combustion. In this study, a flamelet model with a physics based closure for the progress variable dissipation rate is applied for the first time to a spark ignited IC engine. The predictive capabilities of the proposed approach are studied for one operating condition of a gasoline port fuel injected single-cylinder, four-stroke spark ignited full-metal engine running at 3,500 RPM close to full load (10 bar BMEP) at stoichiometric conditions.

Range extender (REx) engines have promise for providing low-cost energy for future battery electric vehicles. Due to their restricted operation range, REx engines provide an opportunity to implement system-level schemes that are less attractive for engines designed for highly transient operation. This paper explores a thermochemical recuperation (TCR) scheme for a 2-cylinder BMW spark-ignition REx engine using a 1-D model implemented in GT-Power™. The TCR reactor employs a unique catalytic heat exchange configuration that enables efficient transfer of exhaust sensible and chemical enthalpy to steam reform the incoming fuel. The engine model without the TCR reactor was validated using experimental emissions and performance data from a BMW engine operating on a test stand. A custom integrated heat exchanger and catalyst model was created and integrated with the validated engine. A parametric modeling sweep was conducted with iso-octane as fuel over a range of reformed fuel fraction.

A standard port fuel injected, unthrottled single cylinder four-stroke SI engine, with a compression ratio of 10.3:1, and using standard gasoline fuel, has been adapted to operate in the homogeneous charge compression ignition (HCCI) mode, by modifying the valve timing. It has been found that over a speed range of between 1300 and 2000 rpm, and lambda values of between 0.95 and 1.1, stable operation is achieved without spark ignition. The internal EGR rate was estimated to be about 60%, and emissions of NOX were typically 0.25 g/kWh. Practical implementation of this HCCI concept will require variable valve timing, which will also enable reversion to standard SI operation for maximum power.