The objective of this paper was to investigate the spray characteristics of methanol and dimethyl ether (DME) on the swirl nozzle of a Stirling engines by comparing with traditional ultralow sulfur diesel fuels (USLD) under different fuel injection rates and different surrounding back pressures in a constant volume pressure vessel. Under the test rig, the macroscopic and microscopic spray characteristics of the fuels were studied by a high speed camera and FAM Laser Particle Size Analyzer during the atomization process. The experimental results show that injection pressure and ambient pressure have a significant impact on the spray tip penetration and spray angles. Higher spray pressure makes the formation period of spray decrease and the penetration rate increase whereas higher back pressure inside the injection chamber leads to the shrinking of the spray angle. The atomization quality of DME under atmospheric back pressure is much better than that of methanol and ULSD while it becomes worse when ambient back pressure is higher than the saturated vapor pressure. Additionally, higher back pressure and a larger injection flow rate are beneficial to the atomization quality of ULSD, whereas those factors seem to have relatively small influence on the droplet size distribution of methanol. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.