The thermal efficiency of an internal combustion engine at steady state temperatures is typically in the region of 25-35%[1]. In a cold start situation, this reduces to be between 10% and 20% [2]. A significant contributor to the reduced efficiency is poor performance by the engine lubricant. Sub optimal viscosity resulting from cold temperatures leads to poor lubrication and a subsequent increase in friction and fuel consumption.
Typically, the engine lubricant takes approximately twenty minutes [3] to reach steady state temperatures. Therefore, if the lubricant can reach its steady state operating temperature sooner, the engine's thermal efficiency will be improved.
It is hypothesised that, by decoupling the lubricant from the thermal mass of the surrounding engine architecture, it is possible to reduce the thermal energy loss from the lubricant to the surrounding metal structure in the initial stages of warm-up.
Using a bespoke oil flow rig described in the methodology section of this paper, it has been demonstrated that the addition of a 2 mm thick nylon tube, increases the maximum temperature differential between the lubricant and surrounding metal by 145% and reduces the energy losses from the gallery by 50%. This results from the addition of both a high thermal resistance material and a contact resistance between the polymer tube and metal.
The insulating performance of nylon has been closely matched by utilising a specially designed aluminium insert with a 0.5 mm air gap. The increased contact resistance of such an insert has been shown to increase the temperature differential by 107% and reduce energy losses by 40%.