Bonzer Words!: Saving Petrol
Colin Fisher gives some tips on fuel-efficient driving.
Reducing carbon emissions, as well as reducing drain on the pocket book, may be enhanced by extracting more miles traveled in your car from a gallon (or liter) of petrol. This statement is difficult to refute. Well, how does one go about doing this? Part of the answer lies in what car you drive and part of it lies in how you drive.
The single most important factor in the 'gas mileage' that characterizes a particular vehicle is the weight, or mass, of the car. It is because, when we drive, we start and stop frequently except for those times when we are cruising at a high speed, because each time that we start out from a low, or zero, speed situation, we must accelerate the vehicle, and all it contains, up to the desired cruising speed. A principle from elementary physics is that the kinetic energy of a moving body is proportional to its mass and to the square of its velocity. Where does this energy come from when we accelerate? It comes from the energy released by burning the petrol required to achieve the final speed of the vehicle.
What can we learn about saving petrol? There are several points here. Firstly, when stopping and starting, keep your maximum speed as low as practicable. Secondly, attempt to keep your car free of extra weight; for example, don't carry heavy articles around that are not immediately needed. And, finally, look to the weight of your car. Do you really need a vehicle that weighs so much; or, could you get by with a smaller and lighter one?
The next important area where petrol can be conserved has to do with how the car is driven. All of the air that enters the car's engine goes through the throttle. You have control of the throttle by means of how far you press down the accelerator pedal with your foot. Let us take a look at the throttle. It restricts the airflow to the engine because, if it did not, the engine would run full out and the car would become a missile. Now, when the engine pulls air through the throttle, there is a pressure drop in the air across the throttle. What this means is that the engine is doing work (expending energy) to pull in the desired amount of airflow. Where do you think that this energy comes from? Why it comes from the petrol that you are burning to provide it. So here is another potential source of loss of energy that does nothing to get the car's driver from point A to point B.
What can the driver do to reduce the loss of energy of getting the combustion air into the car's engine? Well, one thing to do is to think about the transmission when you buy the car. An automatic transmission is designed to shift between adjacent gears at particular points of engine speed (rpm). This is pretty much out of the driver's control since it is built into the car. However, a driver could have purchased a car with a manually-shifted transmission. This allows the car to operate at lower engine speeds providing the car is not 'lugging'. What is lugging? I think that you know what it is. It is when the engine speed is low and there is a sensing that the drive system is beginning to vibrate a bit, as the oil film in the bearings begins to become unstable (that is another topic). Anyway, by keeping the engine speed low, the airflow through the throttle is kept low and the losses owing to pumping air through the throttle are reduced. This can be summarized by the following instructions: 1) keep a light foot on the accelerator; and, 2) stay in as high a gear as quiet and stable operation of the vehicle will allow.
There are other things that you can do to make improvements in the gas mileage of your car. Firstly, maintain the inflation of your tires at the level recommended by the vehicle's manufacturer. Secondly, and perhaps more importantly, pay attention to having the engine of your car tuned as frequently as suggested by the car's manufacturer. And, finally, beware of devices to be added to your car that are offered by third party suppliers and that offer dramatic improvements in gas mileage. Most of these are bogus and might even damage your engine.
Good luck and safe driving.
© Colin Fisher
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Colin writes for Bonzer magazine. Please visit www.bonzer.org.au
