The Effects of the Oil Temperature Warm-Up on Engine Fuel Consumption

The need for even more efficient internal combustion engines in the road transportation sector is a mandatory step to reduce the related CO₂ emissions. In fact, this sector impacts significantly on greenhouse gases worldwide, and the path toward hybrid and electric powertrains has just begun. In particular, in heavy-duty vehicles the full electrification of the powertrain is far to be considered as a really feasible alternative. So, internal combustion engines will still play a significant role in the near/medium future. Hence, technologies having a low cost to benefits (CO₂ reduction) ratio will be favorably introduced in existing engines. Thermal management of engines is today a recognized area of research. Inside this area, the interest toward the lubricant oil has a great potential but not yet fully exploited. Engine oil is responsible of the mechanical efficiency of the engine which has a significant potential of improvement. A faster warm-up during a daily urban trip when the engine starts from a cold state is a good way to reduce fuel consumption (CO₂ emissions) and also harmful emissions, which represent the most critical aspect in urban areas. Conventional oil warm-up takes several minutes to reach a thermal regime, during which inefficiencies related to the low oil temperature are significant.

In this paper, the relation between oil temperature and fuel consumption of a turbocharged diesel engine has been evaluated, matching a theoretical approach with experimental data. The oil warm-up has been registered during a homologation cycle when the engine was managed as light-duty propulsion system. Most part of the working conditions was done with the oil far from a thermal regime, demonstrating poor efficiency and high harmful emissions. Then, several strategies to speed up the oil warm-up have been investigated, characterizing the benefits in terms of CO₂ emissions. Particularly, the use of a thermal storage available on board resulted effective, as well as an eventual heat recovery from exhaust gases which immediately reach a temperature level enough to heat up the oil.