Fuel for Thought

In any job, the quality of the product is only as good as the quality of the workmanship and materials that go into the project. If the intended product is clean air, quality comes from good emissions control technology combined with good raw materials. And the raw material that matters most is fuel. Are modern fuels as good as the engines they burn in?

What are motor fuels?

Considering their importance to the industry, it’s surprising how little most of us know about fuels. We all know that gasoline is an oil product, but what’s the difference between the black stuff that comes out of the ground and the fluid at the gas pump? Oil is a soup of chemical molecules, based on carbon atoms, mostly surrounded by much smaller hydrogen atoms. That’s the origin of the term “hydrocarbon” fuels, and it includes everything from methane, the simplest fuel with a single carbon atom, to complicated molecules like benzene, which has six carbon atoms formed into a ring. How big can these linked-carbon molecules get? In plastics, they can be several hundred thousands of carbons long, but for motor fuels, the number of carbon atoms on the molecules is tightly controlled. Typical components of gasoline (there can be over 500) contain from five to eight-carbon molecules, named pentane, hexane, heptane and octane, after the number of carbons. Crude oil contains many different carbon molecules that must be separated or converted into the “fractions” used to blend gasoline. Other fractions are used for everything from lubricating oils to asphalt.

Other refinery processes like hydrocracking, reforming and alkylation boost the yield of the process by converting other fractions into molecules useful for fuel.

Blending Gasoline

That’s a very rough approximation of a very complex process, but isolating a few desired hydrocarbons from crude oil isn’t enough to make a useful motor fuel. To operate in typical Canadian vehicles, it needs controlled properties such as vapour pressure, anti-knock capability, detergency, and oxidation stability. One critical attribute is called Reid Vapour Pressure or RVP. Vapour pressure is a direct measure of the volatility of a gasoline, which in the Canadian climate is especially important for reliable hot and cold start properties. Cold temperatures require a higher volatility, while the summer climate needs less; on the Reid scale, winter gasolines are about 13psi RVP, compared to summer blends at roughly 8.5 psi RVP. Different carbon molecules can be blended with gasoline to alter RVP, with “smaller” fractions like isobutane (four carbon atoms) raising vapour pressure and heavier fractions lowering it.

Every tech understands engine knock and the causes of preignition and although the combustion chemistry is very complex, the relationship of ignition timing, compression ratio and octane rating has been known for decades.

Tetraethyl lead was the first anti-knock additive, but it’s toxicity and tendency to poison catalytic converters drove its phase-out from 1975. Refiners found alternatives, mainly alcohols and “oxygenates”. Alcohols, (in fuels they’re methanol and ethanol) and “oxygenates” like methyl tertiary butyl ether (MTBE) and methylcyclopentadienyl manganese tricarbonyl (MMT) like lead compounds, have drawbacks. Despite the term “oxygenates”, methanol (and ethanol) also add oxygen to the combustion process, but methanol is corrosive to many fuel system components; check the vehicle’s owner’s manual for specific warnings against using methanol-blended fuels. Ethanol isn’t corrosive or toxic if ingested in reasonable quantities, (it’s the alcohol in beverages like beer, wine and liquor) but it does lower the overall energy content of the fuel, typically replacing 10% of the blend’s volume. Most modern vehicles are designed to run well with ethanol concentrations of up to 10 percent, and when used in winter, ethanol-blended fuels also scavenge water from the fuel system, acting as built-in gas-line antifreeze.

MTBE is a suspected carcinogen that’s either banned or under review in several U.S. states, although it was not found to be toxic in a 1992 Environment Canada study. MTBE issues are mainly due to spills and leakage from storage tanks, as opposed to tailpipe emissions.

MMT is even more controversial, for reasons that directly affect the auto repair sector. Like other oxygenates, it replaces much of the CO and HC-forming aromatic hydrocarbons (benzene is an example), and on engines without modern computer control systems, will drive the combustion stoichiometry lean, reducing HC and CO, but driving up NOx. On modern engines, the O2 sensors detect the lean condition and more fuel is commanded by the ECU to get back to the engine’s design air/fuel ratio. But since the oxygenate doesn’t have energy value, more fuel must be burned, slightly lowering fuel economy. The real argument against MMT, however, comes from the auto manufacturers.

In a study titled “The Impact of MMT on Vehicle Emissions and Durability”, commissioned by the Alliance of Automobile Manufacturers, the Association of International Automobile Manufacturers and the Canadian Vehicle Manufacturers’ Association, MMT was reported to increase emissions and contribute to spark plug misfire, catalyst plugging and OBD II malfunctions.

The major manufacturer of MMT, the Ethyl Corporation, disagrees. In a March 8th press release, the firm stated:

“Ethyl Corporation has been informed by our two largest customers in Canada of their intention to suspend the use of the gasoline additive MMT pending the results of the Government of Canada-sponsored independent third party review. While this suspension will have a negative impact on our Canadian business, Ethyl’s management believes that the suspension is not likely to have a material adverse effect upon the overall financial performance of the Company. MMT is one of the most extensively tested fuel additives in history. While we are disappointed with the decision of our customers, we believe that MMT is an environmentally beneficial product that has proven its effectiveness in real-world use.”

Ethyl has announced support for an independent third-party study into the impact of MMT. According to the company, “the Government of Canada recently released its “Proposed Framework for an Independent Third Party Review of New Information on the Effects of MMT on Vehicle Emissions.” In their proposal, the Canadian Government provided no timetable for the commencement or completion of the review. Ethyl welcomes the independent third party review of MMT, which we believe, when properly designed, conducted and interpreted, will reaffirm that MMT is compatible with modern emission control devices.”

What can you do as a technician or service advisor?

There’s nothing you can do to improve the quality of Canadian fuel, but there is some evidence that an emissions failure or drivability issue with a midlife car or light truck may be fuel-related. Let them know, and consider the possibility of cat damage if you’re changing O2 sensors and plugs to get a dirty vehicle into compliance.

And definitely monitor Web resources such as Environment Canada (www.ec.gc.ca), The Canadian Petroleum Products Institute (www.cppi.ca) and the Canadian Vehicle Manufacturers’ Association (www.cvma.ca). There is a lot more to gasoline and its effect on automotive emissions than can be covered in one article. Watch SSGM for continued coverage.

The Automakers on MMT

The Canadian Vehicle Manufacturers’ Association has published the text of their study on the effects of MMT on emission control systems on their website at www. cvma.ca. The association reports that the study involved 56 vehicles from six manufacturers, each driven 160,000 kilometers over six years. The study is reported to have cost $US 8 million. According to the study, the Low Emission Vehicles at 160,000 km showed:

– 31 % higher hydrocarbon emissions (HC)

– 24% higher oxides of nitrogen emissions (NOx)

– 14% higher carbon monoxide emissions (CO)

– 2% higher carbon dioxide emissions(CO2)

– 2% lower on-road fuel economy

How much energy is stored in one litre of gasoline?

Think gasoline is expensive? Burning gasoline generates heat, and like electricity or even the digestion of the food we eat, we can compare the amount of energy in similar units. One litre of gasoline contains the rough equivalent of 7000 dietary calories. That’s the equivalent of thirty Tim Horton’s chocolate dip doughnuts. Converted to electricity, it’s about 8.5 kilowatt/hours, which works out to roughly 10 cents a kW/h with motor fuel selling in the low 80-cent range. With generator conversion efficiencies of 25-30 percent at best, the cost of running a generator could be 30 cents per kilowatt-hour! Gas generators won’t replace the power company anytime soon.