Cover Story: Homegrown Engine Oil

For researchers and product developers, creating biobased engine oil has been akin to the search for the Holy Grail. For the past 20 years a number of entities have been experimenting with biobased engine oil. Large groups abandoned the search after numerous trials and being faced with ever-changing specifications related to emissions control, while a small group drove a truck using biobased engine oil, licking the dipstick at various stops to make a point for the product’s “environmental friendliness.”

In Europe, others experimented with the Continuous Oil Recycling System (CORS) concept in diesel automobiles.

While complex esters derived from vegetable oils can be stable enough to handle the engine environment, most current vegetable-oil-based technologies have lacked the necessary stability and cold temperature flowability to perform in the engines in the way petroleum engine oils do.

In 2006, after 15 years of research on industrial lubricants and greases, the University of Northern Iowa expanded the scope of the research at its National Ag-Based Lubricants Center (UNI-NABL), Waverly, IA, to include automotive oils and biofuels. The Center’s researchers began to explore the concept of CORS, technology they had briefly worked with 10 years earlier with an agricultural machinery OEM.

CORS was derived from an aftermarket product that was installed on a diesel engine to continuously steal a small amount of engine oil and feed it to the fuel line. A separate reservoir was used to keep the the crankcase full of fresh oil. After a few fuel-ups, the operator would replenish the oil in the add-on tank.

The main problem with this approach was that the burning of used oil resulted in a negative impact on the already difficult-to-achieve emission standards.

Vegetable-based engine oil

UNI-NABL researchers, along with industrial collaborators, modified the CORS concept to use vegetable-oil based engine oils and created a sophisticated black box called the CORS Convertor. The CORS Convertor communicates with the main processor of the engine, and also has its own sensors and transducers to monitor the condition of the oil and fuel. It is an add-on unit that conceptually resides between the crankcase and the fuel injectors and ensures that oil recycling is performed in a way that is beneficial to the engine.

The CORS Convertor uses sensors plugged into the crankcase to monitor the physiochemical conditions of the engine oil, which is a mixture of modified vegetable oils and a minimal amount of performance-enhancing additives. The CORS Convertor continuously draws oil samples from the crankcase. In addition to evaluating the oil, it conditions it as needed, to be used as fuel.

In effect, the CORS Convertor is like a human kidney that ensures what is fed into the fuel system is cleansed of harmful constituents and is only sent to the fuel system when the engine conditions indicate the best time to use this oil as fuel. For example, a cold engine would not receive vegetable-based oil, and the amount of oil that is fed into the fuel system is varied, based on the ability of the engine’s combustion process to provide the cleanest combustion possible.

Where the original idea of feeding used engine oil into the fuel had a negative impact on emissions, combining CORS with the convertor and vegetable oil can improve exhaust emissions.

Target diesel engines for CORS

The initial target market for CORS is stationary diesel engines, where the addition of an oil tank does not present the logistical problems found with limited space on mobile equipment. To test the concept, UNI-NABL prepared three John Deere diesel engines and instrumented them using an eddy current dynamometer to test the engine under various load conditions.