
We have already discussed some of the methods for reducing the emissions from automobiles, and will revisit this topic in more detail in Unit 3 where we discuss pollution and pollution control. Another approach to reducing emissions is the changing the fuel, with the intent of yielding better performance, and reduced emissions.
Tetraethyl Lead

What happened to all the lead?
What happened to all the lead: Text Version (click to reveal)
Dr. Mathews: I can recall in the late seventies, friends of my parents coming to visit us. And they are an American couple and they brought their own car from America. And they were doing the grand European tour. Which is fine because the rest of Europe drives on the wrong side of the road just like you Americans. And there was plenty of unleaded gasoline in Europe as well. But in England, and the whole UK, the issue was a navigation one, you had to travel about 300 miles before you would find another unleaded gasoline station. And so rather than plan a normal trip where you would plan on seeing all the major cities like London, Chester, York, Whales, and the Lake District, they had to do the same kind of trip but planning to hit all the unleaded gasoline stations on the way to fill up. This is in the late 1970s and unleaded gasoline hadn't really started yet in the UK and so it was a major problem. I see very similar issues now if I was to go buy a natural gas power vehicle or even an electric vehicle. I would have to plan my trips very carefully so I could stop at a place where I could recharge or fill up. It is an interesting comparison.
Lead (chemical symbol Pb, for Plumbum) was added to gasoline in the 1920's as an octane booster, and in some cases, to provide lubrication for the exhaust values. There are 2 problems with this approach (the addition of tetraethyl lead) - the first is that the gasoline fumes contained lead, which can enter the bloodstream. Indeed, studies have found that in city children, higher concentrations of Pb were discovered, where low levels of lead in the blood of small children can reduce brain development. (Perhaps this explains my reduced mental capacity? - Na I was a country boy, so it had to have been the cow that kicked me in the head!) The second issue is that while lead was in the exhaust gases, any attempt to use catalytic converters would be thwarted. The lead covers the catalyst, rendering it useless.
But not all the news is bad: the fix to this problem is relatively easy. Simply stop adding tetraethyl lead to gasoline, which is what the US did beginning in the 1970's, Some classic cars, however, did not fair well on unleaded gas, and so they could continue to use leaded gasoline. The former USSR, for instance, and other areas with less modern technology, continue to use leaded gas.
87, 91 or 93?
In America these are the common choices when we go to fill up. In Europe they often sell higher octane value gasoline.

These refer to the octane number of the fuel, and unless you own a high-performance car, 87 is just fine! Just what is Octane
What is Octane Text Version (click to reveal)
[Video opens with Dr. Mathews standing in front of a large machine.] Dr. Mathews: I am here at the energy institute research facility. To my left is an octane rating engine. When you go to buy gasoline from the garage you have a choice of several octanes. Most of you will be buying 87. Iso octane, the octane number, is based on a mixture of iso octane and heptane. When you are buying an 87 octane gasoline, what it means is it will have the same knocking behavior as 87 percent iso octane and 13 percent heptane. The way that is tested is in a device exactly the same as this. What we will do is take an 87 percent mixture of iso octane, a 13 percent of heptane and blend them together, and see how they behave in certain conditions in this particular engine. Then we will compare it with a complex blended mixture of gasoline. Remember gasoline is going to contain hundreds of different compounds. So you are not buying octane, you're not buying iso octane, and you are not buying heptane. They might be there in small quantities but they are not a majority of the components. What we are looking at is knocking behavior. If we get that undesirable, spontaneous combustion when we compress the cylinders and the gasses and the fuel in the air, and it self-ignites, that is called knocking. That is completely undesirable in a gasoline engine but it is exactly how a diesel engine works. [Video ends]
The Basics of Octane:
We assign iso-octane an octane value of 100 and heptane an octane value of 0. When we mix the 2 liquid fuels, we can produce a fuel with knocking properties between 0 and 100. When you purchase an 87-octane gasoline it has the same knocking properties as a mixture of 87% octane and 13% heptane (octane number of zero). It does not imply that the composition of the gasoline is 87% "octane". Gasoline might well contain over 100 different compounds. The (R+M/2) you see on the gasoline pump indicates that the knocking is averaged between two engine conditions (one more stressful on the engine than the other).
The octane number relates to the knocking (premature ignition) of the fuel. When we compress the fuel the temperature of the fuel increases (opposite of our refrigerator) and it can self-ignite before the spark-plug fires. This is a desirable effect in diesel engines, as they do not have spark plugs (which is why radio astronomers drive diesel cars - no spark plugs to give off radio signals). This self-ignition property is known as knocking. It is related to the chemistry (don't panic) of the fuel.
The combustion of the gasoline occurs because of the appropriate mixing of a vapor of the gasoline with air and a spark provided by the spark plug (see left). The battery in the car provides the electricity to create the spark; it is also used to run the radio, lights, and to start the starter motor to start the gasoline motor. The motor needs to turn over so the piston rises in the cylinder, compressing the air and gasoline mixture, which is ignited by the spark. Timing of these events is very important, hence the need for a timing belt. The resulting combustion produces hot gases, which drives the piston down providing the energy to run your car. The starter motor has started the engine and now is no longer needed, until next time.

At left is a static 3-d model of an iso-octane molecule.
The octane that we know from filling our tanks is actually 2, 2, 4 trimethyl pentane (can you see five carbons in a line-that is the pentane part, tri means three (methyls) and methyl is one carbon with 3 hydrogen's, you should be able to find three of them, can you? The molecular formula is C8H18. Can you determine the molecular weight? (Hint: each carbon has 12 amu and H 1 amu (atomic mass units). This is an example of an alkane.
MTBE

When we stopped adding tetraethyl lead we needed to have a replacement octane booster and MTBE was what we chose. Chemically it is methyl tertiary butyl ether.
Can you see the lone oxygen atom? Also notice the highly branched shape that is responsible for higher octane numbers than straight chain compounds. It is the property of the oxygen atom that has resulted in additional uses for MTBE in gasoline to reduce pollution. We'll cover this more in Unit 3, where the discussion shifts to pollution and environmental consequences, this is the condensed version.
Carbon Monoxide (CO)
This is a product of incomplete combustion (not enough oxygen and mixing). It is a lethal, odorless, and colorless gas. The hemoglobin in your blood usually carries oxygen to your cells and removes carbon dioxide. But it would rather "hang out" with carbon monoxide. So if there is enough CO in the air it bonds with hemoglobin and the oxygen does not get delivered to your cells and you die. This is why running engines in enclosed spaces, like garages, is a bad, or fatal, idea.
The oxygen in the MTBE permits better mixing of oxygen and fuel and so there is less CO produced. Normally, your catalytic converter can deal with CO to reduce the concentration (it does not remove all the CO from the exhaust gases) but it only does so when hot. In the winter the catalytic converter takes a while to warm up and so we add MTBE during the winter months. CO in the atmosphere at low levels causes headaches and reduced mental capacity. "Health threats are most serious for those who suffer from cardiovascular disease, particularly those with angina or peripheral vascular disease." Source: EPA

Smog (Ground level Ozone)
Smog is also a health issue in many major cities because that is where the cars are located (and electricity generation, etc). It is a summer issue for the US as smog formation (Smog is a secondary pollutant-meaning we do not release smog but it is formed from primary pollutants or pollutants that we do release) requires: warm temperatures, sunlight, hydrocarbons (such as unburned fuel), and NOx. The presence of MTBE in gasoline lowers the temperature of combustion, which lowers the formation of NOx. MTBE in the fuel provides better oxygen fuel mixing and so fewer hydrocarbon emissions. So the combination of less NOx, and less hydrocarbons = less ozone which is the main component of smog. Much more on "smog" issues in Lesson 09.

So MTBE is great, right? Not exactly - there is one problem.
The oxygen also makes MTBE soluble in water. It is a known carcinogenic at high levels but at very low levels (parts per billion) it imparts a foul taste and odor to drinking water.
The MTBE had been leaking into the groundwater for years in California.
Those underground tanks, which are used to hold gasoline, leak!
We are in the process of banning its use. This makes farmers very happy, because they have the replacement for the oxygenated fuel additives - ethanol (from corn).