In this study, a single-cylinder, water-cooled, direct-injection, compression ignition (CI) engine is operated on the homogeneous charge CI (HCCI) mode using acetylene and diethyl ether (DEE) as fuels. Acetylene is inducted as a main fuel and a small quantity of DEE is injected into the intake manifold for controlling combustion phasing. The engine performance and exhaust emission characteristics are investigated experimentally under various operating conditions. From the results, it is found that brake thermal efficiency of the acetylene-DEE HCCI mode is comparable with that of the conventional CI mode. It has a wide operating range of 0–4.2 bar brake mean effective pressure without exhaust gas recirculation compared with the liquid fuels-HCCI mode. The engine could easily start in the HCCI mode using DEE alone. Nitric oxide and smoke emissions are at ultra-low level. Hydrocarbon emissions are comparatively lower at lower loads and higher at higher load conditions. Carbon monoxide emissions are comparable with that of the conventional CI mode. © 2013 Taylor & Francis.