No description available.

No description available.

No description available.

No description available.

The effect of piston bowl geometry on the performance and exhaust emissions from a modern, high speed direct-injection (HSDI) diesel engine was investigated. Four piston bowl geometry’s (shape) were designed, manufactured and tested in a pre-production HSDI diesel engine installed on an eddy-current dynamometer. A series of experimental tests were performed to determined the optimum injector configuration for each piston bowl shape, the best bowl shape for minimum drive-cycle simulated emissions, and the effect of in-cylinder swirl ratio at various engine operating conditions. Results from computational fluid dynamics (CFD) combustion simulation of extreme injector configurations, correlated well with the experimental trends observed. Full-load testing to determine the optimum injector configuration for each piston bowl shape, indicated that exhaust emissions were very sensitive to the point of fuel impingement on the piston bowl walls. In particular, the trend in the emission of particulates and NOx was explained in relation to the point of fuel impingement, and supported by CFD combustion simulation. The emission of smoke and particulates was found to be dependent on wall wetting and late combustion. Key features for the successful design of future HSDI piston bowl shapes were identified, based on the results form piston bowl comparison tests at a selection of the European drive cycle simulation conditions. The effect in-cylinder swirl ratio on engine performance and emissions was determined. An increase in the rate of mixing and heat release from higher swirl generally raised the emissions of NOx, but reduced smoke formation at low engine speeds. Benefits of an increase in swirl on emissions were negated at high engine speeds due to throttling of the intake charge.

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The combustion of clouds of fuel droplets is of great importance in many industrial applications, such as gasoline and diesel engines, gas turbines and furnaces. Here, efficient combustion has to be combined with minimum noxious emissions. Aerosols also might produce a particularly hazardous explosion risk. To optimise their performance a fundamental understanding of the complex processes in aerosol combustion systems is necessary. A fundamental study of aerosol combustion has been conducted to quantify the parameters of importance. For this, a novel aerosol combustion apparatus was developed, that offers a well controlled environment with respect to aerosol properties, temperature, pressure and turbulence. Aerosols were generated using the Wilson cloud chamber principle of expansion cooling, which produces a homogeneously distributed, near monodisperse droplets cloud. Drop sizes of 10 to 30μm, pressures between 100 and 360kPa and temperatures of 263 to 292K were used. Laminar mixtures between the overall equivalence ratios of 0.8 and 1.2 were studied. A considerable burning velocity enhancement of up to 420% was observed. This enhancement was shown to be a function of drop size and liquid fraction. From the study, it was concluded that burning velocity enhancement probably is caused by the increase in surface area due to wrinkling, caused by the development of instabilities. At low temperature (<275K) the formation and destruction of wrinkles and cells was random. At higher temperatures (>290K) cell formation and division was progressive and traceable, like that observed in gaseous flames. Cellular acceleration at these temperatures was similar to that of gaseous flames. Stretch appeared to have a damping effect on the instabilities, caused by the aerosol. Oscillating flames were observed for some experimental conditions and these also showed enhanced flame speeds. These oscillations were possibly caused by aerodynamic interaction between droplets and gas motion ahead of the flame. Also Stretch and radiation probably influenced these oscillations. Inert glass particles in a gaseous fuel-air mixture had no effect on flame speed or structure. However, water aerosols caused significant burning velocity enhancement (50%). These findings contradict the hypotheses that fuel rich pockets, flame propagation through "easy-toburn" regions or a "grid-effect" trigger instabilities in aerosols. Comparison with a linear stability analysis of heat loss from the flame (Greenberg et al.,1998), yielded good qualitative agreement with the data of the present work.

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Diesel exhaust particulates are the subject of increasingly severe legislation controlling mass emissions throughout the world. Other emissions, which are currently unregulated, are also receiving closer scrutiny. In particular, polycyclic aromatic compounds (PAC), some of which are known carcinogens, are being studied. A total exhaust solvent scrubbing apparatus (TESSA) has been constructed to sample diesel exhaust hydrocarbons, using a solvent mixture to strip organic compounds from exhaust gases. This avoided adsorption of hydrocarbons onto particulates, when fitted close to the exhaust port, and minimised the formation of sampling artifacts. TESSA yielded new information, enabling lighter more volatile organics such as 2- and 3-ringed PAC to be characterised, these could not be collected by a dilution tunnel filter, which trapped particulates effectively but did not sample the hydrocarbons which had remained in the gas-phase. TESSA has proved itself to be uniquely suitable for the sampling of gaseous hydrocarbons with which there is currently an increased interest. Experiments using TESSA have confirmed that there is a contribution to the exhaust from small amounts of fuel passing through the combustion chamber substantially unchanged, as well as from partially burnt or pyrolysed products of combustion. New techniques have been developed to aid the interpretation of data obtained from high resolution gas chromatography and gas chromatography/mass spectrometry, in order to assess the origin of specific groups of compounds within the highly complex samples obtained from diesel exhaust. Naphthalene and phenanthrene were shown to increase their concentration relative to their alkylated derivatives in an exhaust sample when compared to the relative concentrations found in the fuel. These parent compounds were being formed within the combustion chamber, as well as surviving in unburnt fuel. Nitro-PAC were detected only at considerably lower concentrations than had previously been found on dilution tunnel filter samples. Two new methods for assessing the contribution of lubricating oil to diesel exhaust emissions have been developed, and involved matching common peaks in a sample and a lubricating oil standard. The results demonstrated that lubricating oil makes a significant contribution to the total particulates. Increased control of lubricating oil leakage to the exhaust would help to reduce particulate emissions to below the new stringent limits.

No description available.