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The performance, emissions and combustion characteristics of lean mixtures of natural gas and hydrogen were studied in a conventional spark ignited engine. Specifically. mixtures of natural gas blended with 5, 10 and 15 percent by volume hydrogen were considered. Engine performance parameters included power (BH P], thermal efficiency (BTE), specific fuel consumption (BSFC), coefficient of variation in mean effective pressure, cumulative energy release schedule, and emissions of CO, NO,r and hydrocarbons. Major conclusions of the work include: (i) at equivalence ratios leaner than 0.80, improvements in BHP, BSFC, and BTE were significant with hydrogen addition; (ii) significant extension of the lean operating limit to lower equivalence ratios was demonstrated with increasing hydrogen concentrations in natural gas; (iii) emissions of CO, NO,r and hydrocarbons decreased as equivalence ratio was reduced until partial burning became predominant; (iv) hydrogen addition appeared to allow stable engine operation with lower pollutant emissions over a relatively broad range oflean equivalence ratios; and (v) the impact of hydrogen blending on performance and emissions was dependent on the volume fraction of hydrogen, although the functional relationship appeared to be non-linear.

The performance and emissions of a single-cylinder natural gas fueled engine using a pilot ignition strategy have been investigated. Small diesel pilots (2–3% on an energy basis), when used to ignite homogeneous natural gas-air mixtures, are shown to possess the potential for reduced NOx emissions while maintaining good engine performance. The effects of pilot injection timing, intake charge pressure, and charge temperature on engine performance and emissions with natural gas fueling were studied. With appropriate control of the above variables, it was shown that full-load engine-out brake specific NOx emissions could be reduced to the range of 0.07–0.10 g/kWh from the baseline diesel (with mechanical fuel injection) value of 10.5 g/kWh. For this NOx reduction, the decrease in fuel conversion efficiency from the baseline diesel value was approximately one to two percentage points. Total unburned hydrocarbon (HC) emissions and carbon monoxide (CO) emissions were higher with natural gas operation. The nature of combustion under these conditions was analyzed using heat release schedules predicted from measured cylinder pressure data. The importance of pilot injection timing and inlet conditions on the stability of engine operation and knock are also discussed.

The Advanced (injection) Low Pilot Ignited Natural Gas (ALPING) engine is proposed as an alternative to diesel and conventional dual fuel engines. Experimental results from full load operation at a constant speed of 1700rev∕min are presented in this paper. The potential of the ALPING engine is realized in reduced NOx emissions (to less than 0.2g∕kWh) accompanied by fuel conversion efficiencies comparable to straight diesel operation. Some problems at advanced injection timings are recognized in high unburned hydrocarbon (HC) emissions (25g∕kWh) and poor engine stability reflected by high COVIMEP (about 6%). This paper focuses on the combustion aspects of low pilot ignited natural gas engines with particular emphasis on advanced injection timings (45°–60° BTDC). Ignition phasing at advanced injection timings (∼60° BTDC), and combustion phasing at retarded injection timings (∼15° BTDC) are recognized as important combustion parameters that profoundly impact the combustion process, HC emissions, and the stability of engine operation.

The influence of engine operating variables on the performance, emissions and heat release in a compression ignition engine operating in normal diesel and dual-fuel modes (with natural gas fuelling) was investigated. Substantial reductions in NOx emissions were obtained with dual-fuel engine operation. There was a corresponding increase in unburned hydrocarbon emissions as the substitution of natural gas was increased. Brake specific energy consumption decreased with natural gas substitution at high loads but increased at low loads. Experimental results at fixed pilot injection timing have also established the importance of intake manifold pressure and temperature in improving dual-fuel performance and emissions at part load.