Keeping Engines Running Clean
Gasoline additives first appeared un the 1950s when carburetor icing was an issue. Of course, lead anti-knock additives have been used since the early 1920s to boost the octane value of gasoline, but this column will address only those additives tha increase the "performance" of the engine's intake system and combustion chamber--specifically "deposit control additives."
Solving intake system and combustion chamber problems The world of engine technology is changing rapidly to meet environmental regulations and customer expectations. Along with these changes, engine manufacturers are demanding that the fuel, whether gasoline or diesel, change as well. However, with all the debate among regulatory agencies, engine manufacturers and fuel suppliers, the users of the fuels have often been left out of the communication loop. Well, for PE&T readers, that situation started to change significantly with Roger Leisenring’s three highly informative articles on diesel fuel (“The Changing Face of Diesel Fuel Today,” February; “Premium Diesel Fuel: Why the Controversy?” March; and “Driving Home the Impact of Diesel Fuel Properties,” May). And now there is much more to come in PE&T on the vital topic of fuels and additives. Roger Leisenring and several other engineers from Texaco Additives International (TAI, a major worldwide marketer of fuel additives) will share a regular column to provide PE&T readers with straight talk about fuels and fuel additives; they invite your suggestions, comments and questions so that they can address your needs and concerns. In this first column, TAI’s William Bitting and Joe Valentine provide a general overview of gasoline engine problems that have had to be addressed with fuel additives during the past 50 years. Future columns will keep readers updated on current developments in the areas of both gasoline and diesel fuels and additives.Gasoline additives first appeared in the 1950s when carburetor icing was an issue. Those of us who still own old farm tractors or fly aircraft with carburetors remain familiar with this phenomenon. Of course, lead anti-knock additives have been used since the early 1920s to boost the octane value of gasoline, but this column will address only those additives that increase the “performance” of the engine’s intake system and combustion chamber—specifically “deposit control additives.”
Remembering the old days
The history of additives from the carburetor throttle plate to the combustion chamber has evolved over a period of some 50 years. During this time, engine and vehicle technology has undergone extreme changes. For example, typical engine technology in the 1950s included four-, six- and eight-cylinder engines with flathead and overhead valves. These engines were equipped with one-, two- and four-throat carburetors (occasionally multiple carburetors) and had relatively low compression ratios.
Chevrolet offered the Rochester fuel injection system in 1957, but it took many years for electronic fuel injection to become the standard method of introducing fuel into an engine. The 1960s saw Detroit’s “Muscle Car Era” with many production vehicles delivering more than 400 horsepower. Even the family sedan was generally overpowered. These engines were rather robust and could tolerate a buildup of deposits without causing drivers much dissatisfaction.
New engines, new problems
But with the enactment of the federal Clean Air Act, exhaust emissions became an issue in the 1970s. By the 1980s, engines took on a very different look than they had just a few years earlier. When we compare these older engines to the computerized feedback, four-valve, dual overhead cam, all aluminum, electronically fuel-injected engines of today, the need for deposit control additives begins to make sense. Customers now demand that even low-end vehicles perform to greater levels than their low-tech ancestors.
This new generation of engines brought with it deposit-related engine performance problems that manifested themselves as poor starting and idling, stalling, hesitation and reduced fuel economy. When early electronically fuel-injected engines were allowed to hot soak (i.e., were parked with a hot engine), the lower boiling-point components of a droplet of gasoline would evaporate from injector tips, leaving the heavier components as a gummy deposit. In time, the deposits would build up and upset the atomization (and eventually the flow) of fuel from the injector(s). Clearly, deposit control additives were needed.
In the mid-1980s, Bill Bitting (co-author of this column) wrote a technical paper that addressed the intake valve deposit problem in BMW 318i engines (note that we’ve moved deeper into the intake system). Deposits on intake valves upset the smooth flow of fuel and air around the valve and port; and certain deposit morphology can actually absorb fuel, causing that cylinder to run lean. Since oxygen sensors can only detect aggregate exhaust gases, the vehicle computer can be commanded to enrich the mixture, thus causing the remaining cylinders to run rich. This, of course, leads to poor fuel economy and increased emissions.
Shortly after that technical paper was published, Joe Colucci (then head of GM Research) solicited help from the major oil companies to formulate deposit control additives for gasoline. In essence, he challenged oil companies to keep intake systems as clean as when they left the factory and to clean up those that had accumulated deposits.
Intake system cleanliness was (and is) one of the keys to best performance, maximum fuel economy and minimum emissions. Texaco (and others) embraced that challenge and formulated what were to become several generations of intake system deposit control additives. Figure 1 illustrates the generations of additives and their respective performance levels.
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Cleaning up the combustion chamber
Following the solution for intake valve deposit problems, combustion chamber deposits became an issue. Combustion chamber deposits (CCD) can have a negative impact in several areas:
• Octane requirement increase (ORI). ORI occurs when a thermal barrier prevents heat transfer to engine coolant and may cause the engine to knock.
• Increased emissions of oxides of nitrogen (NOx)
• Carbon rap. This occurs when CCD builds up to cause mechanical interference with a piston top and combustion chamber bottom.
• Combustion chamber volume reduction. Reduced volume in the chamber raises the compression ratio in the cylinder with CCD and increases the octane requirement.
The carbon rap problem is fairly new. Even so, that problem and the other problems cited above can be prevented by today’s gasoline additives, available either as an after-market product or already in the gasoline at the pump.
What’s in the works?
In our next column, we will tell you more about today’s additives and where to get them. We will also let you in on some new claims and developments in the gasoline additive area.
Discuss