Homogeneous charge compression ignition (HCCI) combustion of polyoxymethylene dimethyl ethers (PODE)

Polyoxymethylene dimethyl ethers (PODE) are a promising alternative fuel for diesel engines. PODE have high volatility, high ignitability and high oxygen content, and is thus also an ideal additive fuel for blend and dual-fuel combustion due to its low-temperature chemistry. In this work, the characteristics of PODE homogenous charge compression ignition (HCCI) combustion are investigated for the first time. The effects of charge mass equivalence ratio (Φm) and exhaust gas recirculation (EGR) on PODE HCCI are studied. The results indicate that PODE HCCI exhibits two-stage ignition with a strong low temperature heat release (LTHR) before the high temperature heat release (HTHR). HTHR switches from one-stage to two-stage with an increase of Φm due to rapid CO oxidation. At a specific EGR rate, with an increase of Φm, the end-of-compression charge temperature decreases, the ignition timing of LTHR delays. With an increase of Φm, the ignition timing of the HTHR advances at the EGR lower than 42%, but it delays at the EGR of 52% in general. For a specific Φm, with an increase of EGR, the end-of-compression charge temperature decreases, the ignition timing of both LTHR and HTHR delays, and the combustion duration of the HTHR increases. CO emissions decrease with an increase of Φm and a decrease of EGR. Φm and EGR have only a slight effect on HC emissions. This work also provides fundamental data of PODE combustion characteristics for the future development of PODE reaction mechanisms.