NOVELTY - A fuel composition comprises at least one 2-6C alcohol (at least 2.5 vol.%), and at least one 2-6C ester of at least one long chain fatty acid. The fuel composition exhibits a pH of less than 6.8, and/or has a kinematic viscosity of less than 4 centistokes.    USE - As a fuel composition for powering a vehicle having a two-cycle diesel engine (claimed).    ADVANTAGE - The fuel composition exhibits a pH of less than 6.8 (preferably 5.5-6.7) and has a kinematic viscosity of less than 4.2 centistokes. The fuel composition has a cloud point of at least as low as -5 degrees C and a pour point at least as low as -15 degrees C when measured in accordance with ASTM D2500. The fuel composition is free of sulfur and nitrogen atoms. The exhaust of the engine comprises less nitrogen oxides (NOx) species than the exhaust of the engine when combusting petrodiesel. The exhaust of the engine comprises a lower concentration of carbon monoxide (CO) than the exhaust of the engine when combusting petrodiesel. Refining the fuel composition in a slightly acidic condition can provide storage stability benefits. The process can be performed without utilizing external sources of heat, i.e., at or near ambient temperatures. The process can be performed without the addition of significant amounts of water, thereby eliminating the need to collect and treat waste water. The fuel composition can result in simultaneous reductions in opacity, carbon monoxide (CO), sulfur dioxide (SO2), and nitrogen oxides (NOx) in the exhaust compared to the exhaust of the same engine combusting petrodiesel. Simultaneously, the amount of O2 in the same exhaust increases relative to that seen when petrodiesel is combusted. The composition also greatly reduces or removes carbonaceous deposits on metal parts of the engine. The process does not require the use of large volumes of water to wash Group I ions out of the raw fuel composition, thus reducing the amount of water that must be used and treated prior to disposal. Additionally, because excess alcohol in the refined fuel composition is desirable, the process does not require the use of time- and energy-intensive distillation techniques. Thus, in addition to using essentially only natural starting materials, the process requires the input of very little energy to make and refine a fuel composition. The fuel composition can be stored without a need for significant treatments or precautions. By refining the fuel composition in a slightly acidic form, better storage and handling performance can be achieved. The fuel composition provides better fuel efficiency than pure biodiesel products. Use of the fuel composition does not require the use of any special equipment or to require the modification of existing engine equipment.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) providing the fuel composition involving providing a liquid that contains at least one 2-6C ester of at least one long chain fatty acids; adjusting the pH of the liquid to less than 7, to provide a raw fuel composition; and optionally treating the raw fuel composition to remove particulates having an average diameter greater than about 1 mu m, and to provide a refined fuel composition; and    (2) method for powering a vehicle, involving introducing to the engine of the vehicle a fuel that comprises ethanol (at least 2.5%) and at least one 2-6C ester of at least one long chain fatty acid, where the fuel has a kinematic viscosity of less than 4 centistokes; and permitting the engine to combust the fuel to power the vehicle.