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Due to the global drive for carbon neutrality, passenger vehicle gasoline engines are transitioning to higher levels of electrification, such as hybrid electric vehicles and plug-in hybrid electric vehicles, HEVs and PHEVs. Compared with conventional internal combustion engine (ICE) vehicles, the HEV or PHEV engine whilst in ICE only operation, typically operates for multiple shorter periods, in turn the engine coolant and lubricant temperatures are lower. Conventional internal combustion engines are often able to yield valuable fuel economy benefits by selecting appropriate engine lubricating oils, typically employing reduced viscosity and suitable additives. There are commercial engine tests available for measurement, often in an engine test cell for precision. Steady state testing is also a simplified option. Such efforts require care, as the accurate measurement is technically and practically challenging.

Due to the global drive for carbon neutrality, passenger vehicle gasoline engines are transitioning to higher levels of electrification, such as hybrid electric vehicles and plug-in hybrid electric vehicles, HEVs and PHEVs. Compared with conventional internal combustion, ICE only operation, the combustion engine in a HEV or PHEV typically operates for shorter periods. In turn the engine coolant and lubricant temperatures are often lower. Such cooler engine running is particularly noticeable for a variety of conditions including short journeys in charge-sustaining mode, urban motoring, a journey length towards the end of the electric range, at cold ambient temperatures, or a combination of these conditions. All C-type piston rings allow limited combustion gases to escape through the ring end-gap.

Measuring lubricant related fuel economy of internal combustion [IC] engines presents technical challenges, due to the relatively small differences attributable to lubricants. As engine technology progresses, large benefits become harder to find; so the importance of precise measurement increases. Responding to the challenge of meeting CO2 targets, many successful IC engine technologies have been deployed; these include downsizing/rightsizing[1], mechanical efficiency improvements, advanced charging and combustion systems, thermal management, sophisticated electronic control and calibration. These technologies have been deployed against a back-drop of increasingly stringent emission requirements. Increasing attention is focused on technologies which offer smaller but important contributions. The search for smaller improvements combined with growing engine and vehicle technology complexity increases the challenge of producing high quality data.