A water/diesel emulsion was used as the pilot fuel in a dual-fuel engine, whilst using LPG as the primary energy source. The water/diesel ratio was 0.3:1 by mass. A single-cylinder air-cooled diesel engine was tested at various loads and LPG fuelling rates, with two injection timings and both the emulsion and neat diesel as pilot fuels. At full load, the emulsion led to an improvement in the brake thermal efficiency of about 3% over the use of diesel as the pilot. However, it was not advantageous at low loads. There was a significant reduction in the NOx emissions with the emulsion but there was an adverse effect on HC and CO emissions. The ignition delay was higher with the emulsion. This led to a rise in the heat release rate in the early combustion stage and, hence, the maximum rate of pressure rise was also higher. Advancing the injection timing increased the brake thermal efficiency at medium outputs with both diesel and water/diesel emulsion. However, it was not advantageous from the point of view of emissions. The use of the emulsion did not increase cyclic variations in combustion.