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Diesel spray experimentation at controlled high-temperature and high-pressure conditions is intended to provide a more fundamental understanding of diesel combustion than can be achieved in engine experiments. This level of understanding is needed to develop the high-fidelity multi-scale CFD models that will be used to optimize future engine designs. Several spray chamber facilities capable of high-temperature, high-pressure conditions typical of engine combustion have been developed, but because of the uniqueness of each facility, there are uncertainties about their operation. For this paper, we describe results from comparative studies using constant-volume vessels at Sandia National Laboratories and IFP.

Seven shapes of piston crowns have been evaluated for their ability to reduce HCCI knock and transmission of combustion noise to the engine. The performance of each piston crown was evaluated with measurements of cylinder pressure, engine vibration and acoustic sound pressure measured one meter away from the engine. The experiments were conducted in a diesel engine that was run in HCCI combustion mode with a fixed quantity of DME as fuel. The results show that combustion knock is effectively suppressed by limiting the size of the volume in which the combustion occurs. Splitting the compression volume into four smaller volumes placed between the perimeter of the piston and the cylinder liner increased the noise to a higher level than that generated with a flat piston crown. This was due to resonance between the four volumes. Using eight volumes instead decreased the noise.

Lean burn operation is often used for improving the efficiency of SI engines. However, as a draw back, this method leads to a higher emissions of Unburned Hydro-Carbons, UHC, compared to stoichiometric combustion. In order to gain a better understanding of what is causing the higher UHC emission at lean burn condition, engine experiments have been carried out on a four-cylinder natural gas fueled SI engine. The concentration of UHC in the exhaust manifold and the HC concentration in the vicinity of the spark plug have been measured during the experiments using a Fast Response FID (FFID) analyzer. Using a model describing the outflow from the cylinder during the exhaust stroke and the measured UHC concentration in the manifold near the exhaust valve, the UHC emissions from the individual cycles have been determined. The investigation showed that under lean burn conditions, cycle by cycle variation had a significant importance on the total UHC emission from the engine.

Engine experiments have been conducted on a gas fueled SI engine. The engine was fueled with natural gas and mixtures of natural gas and hydrogen containing producer gas in order to examine the effect of addition of producer gas on the combustion process and the engine-out emissions. The experiments showed that addition of producer gas decreased the UHC emission at conditions leaner than λ=1.40. The CO emission was increased by addition of producer gas. This was mainly caused by unburned fuel CO from the producer gas. No effect of producer gas on the NOx emission was detected. Formaldehyde, which is suspected to cause odor problems from natural gas fired engine based power plants, was measured using FTIR. The investigation showed that the formaldehyde emission was decreased significantly by addition of producer gas to natural gas.

The paper describes the optimization of a 50 cc crankcase scavenged two-stroke diesel engine operating on dimethyl ether (DME). The optimization is primarily done with respect to engine efficiency. The underlying idea behind the work is that the low weight, low internal friction and low engine-out NOx of such an engine could make it ideal for future vehicles operating on second-generation biofuels. Data is presented for the performance and emissions at the current state of development of the engine. Brake efficiencies above 30% were obtained despite the small size of the engine. In addition, efficiencies near the maximum were found over a wide operating range of speeds and loads. Maximum bmep is 500 kPa. Results are shown for engine speeds ranging from 2000 to 5000 rpm and loads from idle to full load. At all speeds and loads NOx emissions are below 200 ppm and smokeless operation is achieved. Design improvements relative to an earlier prototype are described.

Development of numerical tools for quantitatively assessing biofuel combustion in Internal Combustion Engines and facilitating the identification of optimum operating parameters and emission strategy are challenges of engine combustion research. Biofuels obtained through e.g. a Fischer-Tropsch process (FT) are complex mixtures of wide ranges of high molecular weight hydrocarbons in the diesel and naphtha boiling range dominated by C10-C18 hydrocarbons in n-alkane, iso-alkane, alkenes, aromatic and oxygenate classes. In this paper modeling of combustion in a rapid compression machine has been performed using model compounds from a given FT biofuel distribution as surrogate fuels. Furthermore, the detailed mechanism has been reduced by applying an automatic necessity analysis removing redundant species from the detailed model.

The effects of methanol and EGR on HCCI combustion of dimethyl ether have been tested separately in a diesel engine. The engine was equipped with a common rail injection system which allowed for random injection of DME. The engine could therefore be operated either as a normal DI CI engine or, by advancing the injection timing 360 CAD, as an HCCI engine. The compression ratio of the engine was reduced to 14.5 by enlarging the piston bowls. The engine was operated in HCCI mode with DME at an equivalence ratio of 0.25. To retard the combustion timing, methanol was port fuel injected and the optimum quantity required was determined. The added methanol increased the BMEP by increasing the total heat release and retarding the combustion to after TDC. Engine knock was reduced with increasing quantities of methanol. The highest BMEP was achieved when the equivalence ratio of methanol was around 0.12 at 1000 RPM, and around 0.76 at 1800 RPM. EGR was also used to retarding the timing.

A thermodynamic analysis based on a pressure-time history measured during the combustion in a SI engine is a commonly used tool used for analyzing the combustion process. Both one-zone and two-zone models have been applied for this purpose. One of the major sources of the emission of unburned hydrocarbons from SI engines is the presence of crevices in the combustion chamber where a part of the unburned fuel-air mixture is trapped during the compression and the combustion. In this paper a three-zone heat release model including the effect of crevices is presented. The model is based on a thermodynamic analysis of three connected zones consisting of burned gas, unburned gas and gas trapped in crevices. Engine experiments have been carried out on a natural gas SI engine. The results from these experiments have been analyzed by the model.

This work concerns the modelling of soot formation process in diesel spray combustion under engine-like conditions. The key aim is to investigate the soot formation characteristics at different ambient temperatures. Prior to simulating the diesel combustion, numerical models including a revised multi-step soot model is validated by comparing to the experimental data of n-dodecane fuel in which the associated chemistry is better understood. In the diesel spray simulations, a single component n-heptane mechanism and the multi-component Diesel Oil Surrogate (DOS) model are adopted. A newly developed C16-based model which comprises skeletal mechanisms of n-hexadecane, heptamethylnonane, cyclohexane and toluene is also implemented. Comparisons of the results show that the simulated liftoff lengths are reasonably well-matched to the experimental measurement, where the relative differences are retained to below 18%.

Application of a known hydrogen containing fuel called reformed natural gas (RNG) has been realized in a stationary combustion engine with success. The aim for this is to reduce unburned hydrogen emissions (UHC) from the engine together with an increase in efficiency. The fuel contains mainly methane, hydrogen and minor amounts of carbon dioxide. A small-scale unit for onboard production of RNG has been built in order to avoid the dependence of artificial supplementation of hydrogen. The production is carried out through means of steam reforming of natural gas. The RNG-unit together with theoretical considerations for estimating fuel composition and issues of caution are described. Theoretical studies show a potential for varying the hydrogen content between 8 and 30 vol%. Studies also show potential for remarkable increases in the methane number relative to that of the natural gas. A test engine has been fueled with RNG.