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.