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A study of combustion in a dual-fuel compression ignition engine was conducted to determine the effects of the gaseous fuel addition on the several properties of the combustion process. In particular, the presence and intensity of both end gas knock and diesel knock were measured. A CFR research engine was equipped to run as a dual-fuel engine. Natural gas blends were used for the gaseous fuel fraction, and diesel pilot injection was used as the ignition source. The engine was run at an overall equivalence ratio of 0.7, with premixed equivalence ratios ranging from 0.2 to 0.5. The intake temperature was also varied from 66-110°C. Cylinder pressure data was collected at each point. Three separate methods were used to measure the knock behavior of the engine. Two of these methods were used to quantify the amount of end gas knock which was occurring. Cylinder pressure records were used to calculate a non-dimensional knock factor.

The composition of natural gas delivered through the pipeline varies with time and location around the USA. These variations are known to affect engine performance and emissions through changes in fuel metering characteristics and knock resistance of the fuel. High output, low emissions natural gas engines are being developed that take advantage of the high knock resistance of natural gas. These optimized engines are operated close to knock-limited power where changes in fuel knock resistance can cause operational problems. Octane tests were conducted on natural gas blend fuels using a CFR octane rating engine. Two relationships between motor octane number and fuel composition were established. A correlation for motor octane number versus the reactive hydrogen-carbon ratio was developed, and octane weighting factors, which used the molar composition of the fuel to predict motor octane number, were also found.