You state that in lower temperatures diesels use more fuel. What is the thermodynamic basis for this statement? I find it difficult to figure out why this should be. I have thought of the following: 1) low temperatures means the engine takes longer to reach operating temperature (exacerbated by the greater mass of a diesel engine), but this should only be a problem for very short journeys, as with petrol engines. 2) lower induction air temperature (even after passing through a turbo) could lead to a lower adiabatic compression temperature on the compression stroke, would that really make a significant difference, especially in a 'hot' engine? 3) as with all injection systems, the pump delivers a volume, but the energy depends upon the mass delivered. At lower temperatures a given volume has a greater mass, but that should be self-compensating by adjustment of the foot on the accelerator. The mass delivered can be affected by the specific gravity of the fuel, which can vary a little from source to source and hence affect the consumption, but to this extent?