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There is continuing interest in understanding how fuel, fuel additives, and lubricants contribute to combustion chamber deposit (CCD) weights and compositions in order to better anticipate the impact of CCD on exhaust emissions and engine performance. For this reason, we have characterized a range of CCDs from bench engines and vehicles using solid state 13C Nuclear Magnetic Resonance Spectroscopy (NMR) and X-ray Photoelectron Spectroscopy (XPS). Differences in CCD composition and structure were related to the fuel, fuel additives, and engine oil used in the test. CCDs derived from most fuels run in modern engines are predominantly organic. The fraction of aromatic carbon ranges between 24 and 74% depending on fuels and test conditions over a test length of 1,000 to 20,000 miles. These aromatic carbons exist in predominantly 1 and 2 ring structures that are independent of the amount of aromatic carbon in the CCD.

Direct cylinder injection for hydrogen-fueled piston engines was studied experimentally with an ASTM-CFR engine. An injection scheme was devised for which the combustion occurs during the period of hydrogen injection so that little unburned hydrogen accumulates in the cylinder. This scheme should preclude flashback and preignition, and lowers the rate of cylinder pressure rise to acceptable levels. The potential of hydrogen as a low pollution fuel was investigated by comparing the NOx emissions from the same engine operated on hydrogen and hydrocarbon fuel. NOx emissions for hydrogen are very low provided the equivalence ratio is less than 0.5, and provided the hydrogen and air are well mixed. For equivalence ratios greater than 0.5, NOx emissions for hydrogen fuel were higher than for hydrocarbon fuel. With hydrogen injection, indicated mean effective pressure was varied between 0.07 MPa and 0.78 MPa without intake air throttling.