Early model vehicles used a carburetor to get fuel into a car engine. In carbureted vehicles, fuel is picked up from the fuel tank by an engine-driven fuel pump. The fuel travels to the carburetor, where it fills up a float bowl. When the fuel bowl is full, a needle closes off the passage and stops the fuel flow into the carburetor until the fuel level once again drops. The engine vacuum sucks the fuel out of the carburetor through metering devices, which keeps the mixture at 14 parts of air to 1 part of fuel. This is the optimum mixture for the best combustion within the cylinders of the engine.
All gasoline engines are four-stroke designs. An engine has an intake stroke where the intake valve is open and the piston is moving downward, creating a vacuum that sucks the fuel into the cylinder. The next stroke is the compression stroke. The intake valve closes, and the piston begins to move upward and compresses the fuel in preparation for ignition. The third stroke is the power stroke. The piston is approaches the top of the cylinder in the compression stroke. Just before it gets to top dead center, the spark plug fires and ignites the fuel. The fuel rapidly expands and pushes the piston down with great force. The last stroke is the exhaust stroke. In this stroke, the piston completes the power stroke and begins to rise again. At this point the exhaust valve opens, and the piston forces the exhaust out of the cylinder in preparation for the intake stroke.
Fuel quality is more important on present-day cars than the octane rating. Fuel quality can vary widely with brands and dispensing stations. Most vehicles will run on the lowest octane fuel. The vehicles for which the manufacturer recommends a mid or premium gasoline will also run on regular 87 octane with no more than a 5 percent difference in fuel mileage. Mid-grade and premium fuel on the market today have more additives to clean injectors and valves with a small amount of additive to prevent pre-ignition in high-performance, high-compression vehicles.
With all the technology and advanced computers today and with the addition of knock sensors, even the most high-performance cars can safely run on 87 octane. In the past, the high-compression engines were very prone to pre-ignition, which could be destructive to the engine. Lead was added to the gasoline to make it less volatile. These engines had no way of adjusting the ignition to eliminate this effect. With today's computers, the ignition is constantly being monitored and adjusted to prevent this pre-ignition.
The reason one fuel seems to run better than another in a car is because less preventative maintenance or fewer precautions to prevent contamination have been taken somewhere between production to pump. Fuel has so many ways of becoming contaminated. In short, the refiner has a great deal to do with having a consistent product.
Fuel is transported mostly by pipeline or by ocean-going tankers. The fuel pipeline can become clogged from contaminants. A plug is pushed through the pipes to unplug them. The contaminants removed end up in the line. Ocean-going tankers use huge holds for the fuel. When the hold is empty, they force water into the holds to balance the ship. This water is a contaminant, and it also causes rust to form in the hold. The fuel goes from these sources to holding tanks. Because fuel tends to expand and contract with the temperature and creates a continuously changing pressure, most of the tanks have floating tops. The top of the tank will rise and lower with the level and pressure. The exposed metal is open to the elements and will rust.
All terminals mix mid-grade and premium fuel additives at the terminal as it is pumped into the trucks. How well this is monitored is an important consideration. The fuel tanker trucks have a tendency to rust inside if left empty for a few days. Dispensing of the fuel from the tanker to the holding tank at the station also contributes to contamination. The tanks at the station can also rust when not kept full for a period of time.
The last line of defense to prevent a car from getting these contaminants into the tank is a filter in the pump. If the service station does not change the filter often enough or gets tired of changing the filter due to continuously plugging up with contaminants, they have been know to install blanks. These blanks have been found in many stations. They would allow free flow of contaminants to the car. Taking all this into consideration is just good food for thought. How to avoid this is just conjecture at this point. Best bet is to use stations that appear well kept, and if the fuel from this facility works well in the car, restrict the refueling to this or similar stations.
