Engine test cycle development to evaluate effect of oil formulation on emulsion formation
With the increased number of hybrid vehicle applications in the market, there is an increased concern regarding the formation of water-in-oil and fuel-in-oil emulsions due to the absence of sustained engine operation. In hybrid or plug-in hybrids, the electric drive system is providing much of the power needed for low speed commuting cycles. When engine oil is not allowed to reach operating temperature, there can be a build-up of water and fuel in the oil that can lead to emulsification of the oil and white sludge in the valve train. The white sludge can sometimes be seen under the oil cap and has led to consumer complaints. The current suggested solution is to drive the hybrid vehicle on the highway to bring the oil to operating temperature to burn off the water and fuel in the oil. Due to a desire to better understand this phenomena and evaluate the performance of different oil formulations, a two-stage test development was selected. The study described in this paper outlines the first stage of the development with a modified Sequence VH (GF-6 sludge test) stand to show the repeatable formation of emulsions and study gasoline engine oil related effects. Moving forward, multiple oil formulations will be tested to evaluate the ability of the test to discriminate between oils. In the future, a similar test is planned to be developed for a Prius Prime engine stand using a realistic cold-weather driving cycle to evaluate the impact of field conditions on different oil formulations.