EGEE 101
Energy and the Environment

Gasoline Engines

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Horsepower Past & Present

farmer riding behind six horses pulling the plow.
From the days when the term "horsepower" meant, literally, horsepower.
Credit: USDA

When men get together to discuss their prized vehicles, you can be practically guaranteed that the conversation will include, or completely be dominated by, talk about horsepower. Before the motor vehicle, the horse was the vehicle of choice, the power source for moving supplies and goods, and a primary source of power behind the United State's early agricultural and industrial prominence.

The horse essentially did work for its owner. The more powerful the horse the more work it could do. A standard horsepower was defined as the mass that a horse could move in a specified time period. Suffice to say that since horsepower represents a rate of doing work, more horses means more work could be done, or the same work could be done more quickly. Standard lawn mower or snow blower engines now weigh in around 5 horsepower, riding mowers might be closer to 15, a typical car is in the neighborhood of 100-150 HP, and for you race car types, there are typically several hundred (figurative) horses under those hoods.

The Workings of Gasoline Engines

Please watch the following (:15) video:

img caption here
Click for a transcript.

[Video opens with a close-up of a spark plug.] [The spark plug it fed electricity and a blue spark is seen.] [We hear the noise of a loud shock.] [This is repeated several times.] [Video ends]

video credit here

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. The 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.

Thus, the basic four strokes (for a 4 stroke engine) are:

Four Basic Engine Strokes
Engine Stroke Description
Intake Stroke Air and gasoline (sprayed in a fine mist to permit better mixing of the air and gasoline) enter the cylinder.
Compressions The piston head rises, compressing the air/fuel.
Combustion The spark ignites the combustion/detonation, which rapidly pushes the piston down (via a crankshaft connection; turns the vehicle's wheels).
Exhaust The products of combustion are vented out of the cylinder on the way to the catalytic converter and the tailpipe.

Once again, I suggest that the curious amongst you take a trip to the "How Stuff Works" website to see a more detailed presentation of How Engines Work.

The Gas Alternative?

Car battery
With any luck, you don't have to see this too often.
Credit: JPM

The lead acid battery that sits under the hood in nearly all our cars is heavy, and not inexpensive (especially if you leave your lights on regularly). Considering the size and weight of this battery, and its purpose to just start your car, you can imagine the size, weight, and expense of the one that would be needed to actually power your car? This is the major reason that electric cars running on stored electrical power did not make it off the golf course and onto the roads

Interestingly, living in England, the milk would be delivered to your doorstep, every day except Sunday, by a fleet of electric "milk floats" which started in the 1970's. As we will discuss later, many of the new approaches in vehicles and fuels will occur in those organizations with a large fleet of vehicles.

Who's That Knocking? - The Story of Octane

Gas Pump
We pull up to the pump often once a week to fill the tank. It is convenient, and there are over 100,000 locations in the US to "fill 'er up." You do have a choice, however, between several gasoline's of various octane numbers, determined by the (R+M)/2 method! Eh? Read on.
Credit: JPM

When the Model T Ford was filled up with gas, variations in the production and quality of the gasoline sometimes caused "knocking" in the engine. This violent shaking of the engine caused excessive wear on the engine and limited its power. The cause was the self-ignition of the gasoline and air mixture on the compression stroke (2nd stroke - remember?). In a diesel engine, this is actually desirable, as they don't have spark plugs, but in gasoline engines, it's not a good thing. The knocking is related to the shape, size, and type of molecules found in the gasoline, which is pretty complex stuff - when you account for the added cleaning compounds and environmental packages, your gasoline can include over 100 separate compounds! Please watch the following (1:15) video:

Dr. Mathews expounding on the subject of Octane ratings and Knocking.
Click for the transcript.

[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 at least a hundred different compounds. So you are not buying octane, your 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]

video credit here

Basic Environmental Issues

Back of a car with the exhaust labeled as carbon dioxide– N O x, unburned hydrocarbons, and carbon monoxide.
The exhaust of my Corolla is spewing out the gasses (engine has just started) that are of environmental concern.
Credit: JPM

This knocking can be eliminated by changing the composition (or size, shape, and type) of the compounds. One of the early octane booster compounds added to gasoline was tetraethyl lead. This has been banned now to reduce lead vapors that end up depositing lead in the bloodstream, which resulted in reduced mental capacity, particularly in children.

A bit more about lead.

Click for text description. This will expand to provide more information.
Dr. Mathews: Lead, or more specifically tetraethyl lead, was added to gasoline to increase the octane number. It's palely branched molecule has a very high octane number. And so is useful in helping prevent knocking. The secondary use is that the lead would vaporize in the cylinder, and some of it would go out the exhaust, but some of it would help coat the inside of the cylinders. And so a number of cars took advantage of that and used lead as a natural lubrication. Unfortunately, the lead would leave through the tailpipe and would generally concentrate in the brains of young children. Lead in the air would be breathed in and unfortunately does not exit the body. And so high levels of lead, highly detrimental, and actually reduced brain capacity in small children and young children. And so one of the reasons for getting rid of it was the fact that it is detrimental to your health. We have the same problem in houses built before something like 1974 where another lead compound was added to paint for a couple of reasons. One is the pigments in it, you could get some nice bright whites and also that the bugs would not like to eat it very much because of that lead content. The main reason though that lead was taken out of gasoline was that the lead would have coated any catalyst in the catalytic converter, preventing it from working. So prior to the invention of catalysts, catalytic converters for your vehicle, the lead had to be essentially taken out, or actually not added, to the gasoline.

Now we are required to make many changes to our gasoline recipe to meet environmental challenges (more on this in the next lecture).