The effects of air and exhaust gas dilution on the CAI combustion of a range of fuels including three gasoline compositions, four primary reference fuels, and two alcohols are experimentally investigated using a single cylinder research engine. Two of the three gasolines tested are manufactured from standard gasoline during engine operation by a novel fuel system, designed to improve the performance of both controlled autoignition and spark ignition engines. A series of experimental tests are performed to establish the satisfactory combined air and exhaust gas dilution regions for each fuel. Detailed in-cylinder pressure and exhaust gas speciation measurements are taken, and the fuels are compared and contrasted for their performance in terms of power output, fuel consumption, and harmful exhaust emissions. Results show that alcohol fuels are superior to hydrocarbon fuels for controlled autoignition combustion because their autoignition characteristics are less affected by the presence of exhaust gas species. Furthermore, the timing of autoignition is shown to be of minor importance for achieving efficient and stable controlled autoignition combustion, contrary to widely held beliefs. In addition, the novel fuel system is developed and commissioned for use on a single cylinder research engine operating with a spark ignition system. The two gasoline fuels produced by the system are evaluated individually for their knocking combustion characteristics over a range of compression ratios and spark advances. Results from these tests indicate that the fuel system used in conjunction with a specially modified production engine may allow the normal compression ratio of that engine to be increased by up to 1.0, increasing its efficiency.

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.

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