Butanol-Diesel Blends for Partially Premixed Combustion

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 current paper presents a summary of the performance of such BuOH-diesel blends with respect to emissions and efficiency in the Partially Premixed Combustion regime. Besides a presentation of the sensitivity to injection strategies, dilution levels and fuel pressure, emission performance is compared to upcoming legislated emission levels. The effect of the blend ratio on load ranges is shown and conventional diesel combustion benchmarks are used to show improvements in indicated efficiency. Butanol-diesel blends are shown to be a viable approach to partially premixed combustion, with its high soot reduction potential and stable operation. EURO VI emission levels can therefore be achieved, with moderate or slightly increased fuel pressure. Combustion efficiency is shown to be very reasonable over the whole load range, similar to that of conventional diesel combustion. Combined with an improved thermal efficiency a moderate butanol-diesel blend is shown to have an average gross indicated efficiency of 50% over the whole load range.