Effects of H2 on the number concentration of particulate matter in diesel engines using a low-pressure loop exhaust-gas recirculation system

•We examine effects of H2 on the number concentration of PM emission of diesel engine.•The PM reduction increased as H2 energy fractions, engine load, and A/F ratio increased.•The PM emission could increase by H2 addition at 21.9 A/F ratio.

We investigated the effects of H2 on the number concentration of particulate matter (PM) emissions from a diesel engine fitted with a low-pressure loop exhaust gas recirculation system. We used a 2.2-L four-cylinder direct-injection diesel engine satisfying EURO V regulations, and converted this engine to include an H2 feed. The air/fuel (A/F) ratio was varied in the range of 21.9–45.5 and the brake mean effective pressure was varied in the range of 2–6 bars to control the O2 concentration and in-cylinder temperature, both of which are significant for PM emissions. The number concentration of the emitted PM was measured using a scanning mobility particle sizer. We found that the emitted PM decreased by the addition of H2 which caused the unburned gas temperature increased. Furthermore, the degree of reduction was larger as the A/F ratio, load, and H2 energy fraction increased. However, with A/F ratios of less than 21.9, the addition of H2 increased the number concentration of emitted PM which was attributed to the small O2 concentration at these A/F ratios.