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Partially Premixed Combustion has shown the potential of high efficiency, emissions of nitrogen oxides (NOx) and soot below future emissions regulations, and acceptable acoustic noise. Low-octane-number gasoline fuels were shown to be most suitable for this concept, with the reactivity determining the possible load range. Other researchers have used several refinery streams, which might be produced by a refinery if they were required to do so without additional investment. Some of refinery streams are, however, not expected to be commercially available on the short term. For the present investigation, n-butanol (BuOH) has been selected as a blend component in diesel, and is used from 50 - 100%. The blends then have a reactivity range similar to the refinery streams, so single-cylinder engine tests for their emission and efficiency performance can also be used to determine their applicable load range.

The concept of Partially Premixed Combustion is known for reduced hazardous emissions and improved efficiency. Since a low-reactive fuel is required to extend the ignition delay at elevated loads, controllability and stability issues occur at the low-load end. In this investigation seven fuel blends are used, all having a Research Octane Number of around 70 and a distinct composition or boiling range. Four of them could be regarded as ‘viable refinery fuels’ since they are based on current refinery feedstocks. The latter three are based on primary reference fuels, being PRF70 and blends with ethanol and toluene respectively. Previous experiments revealed significant ignition differences, which asked for further understanding with an extended set of measurements. Experiments are conducted on a heavy duty diesel engine modified for single cylinder operation. In this investigation, emphasis is put on idling (600 rpm) and low load conditions.

Reactivity controlled compression ignition through in-cylinder blending gasoline and diesel to a desired reactivity has previously been shown to give low emission levels and a clear simultaneous efficiency advantage. To determine the possible viability of the concept for on-road application, the control space of injection parameters with respect to combustion phasing is presented. Four injection strategies have been investigated, and for each the respective combustion phasing response is presented. Combustion efficiency is shown to be greatly affected by both the injection-timing and injection-strategy. All injection strategies are shown to break with the common soot-NOx trade-off, with both smoke and NOx emissions being near or even below upcoming legislated levels. Lastly, pressure rise rates are comparable with conventional combustion regimes with the same phasing. The pressure rise rates are effectively suppressed by the high dilution rates used.

Partially Premixed Combustion has shown the potential of low emissions of nitrogen oxides (NOx) and soot with a simultaneous improvement in fuel efficiency. Several research groups have shown that a load range from idle to full load is possible, when using low-octane-number refinery streams, in the gasoline boiling range. As such refinery streams are not expected to be commercially available on the short term, the use of naphtha blends that are commercially available could provide a practical solution. The three blends used in this investigation have been tested in a single-cylinder engine for their emission and efficiency performance. Besides a presentation of the sensitivity to injection strategies, dilution levels and fuel pressure, emission performance is compared to legislated emission levels. Conventional diesel combustion benchmarks are used for reference to show possible improvements in indicated efficiency.