Wednesday, June 4, 2008

Thank Gasoline

TGIT - Thank Gasoline It's Thursday Green Thursday

This week’s blog is brought to you courtesy of that amazing liquid we call gasoline. The average motorist uses two gallons of gasoline a day. This does not sound like a huge amount, however when multiplied by the over two hundred million vehicles in the USA, it is a vast volume of fuel. Gasoline is a mixture of compounds containing carbon and hydrogen atoms (hydrocarbons). This mixture typically has two hydrogen atoms for each carbon atom. Natural gas is composed primarily of methane and has four hydrogen atoms for each carbon atom.

If one did quick but incorrect math, one may believe that using natural gas instead of gasoline as a transportation fuel would halve your carbon footprint. Doing the math correctly by applying the atomic weights of carbon and hydrogen, and the heats of combustion of methane and gasoline, natural gas as a transportation fuel instead of gasoline will lower your carbon footprint by just over twenty percent. The problem is that natural gas is much more difficult to store onboard a vehicle, therefore only a very few vehicles have been converted to run on compressed or liquefied natural gas.

Each gallon of gasoline has 115,000 British Thermal Units (BTUs) of heating value. A BTU is the amount of energy needed to increase the temperature of one pound of water by one degree Fahrenheit. When you take a five minute shower with the water flowing at two gallons per minute at 100 degrees Fahrenheit, you have consumed 3,336 BTUs if the cold water entering your water heater had a temperature of 60 degrees Fahrenheit. Your water heater is 80% efficient, therefore one gallon of gasoline, if used to fuel a water heater, could provide the energy for almost all the showers you take in a month. We have flow restrictors in our showers to conserve hot water but we are barking up the wrong tree when it comes to saving energy in large measure. We should have flow restrictors in our automobiles.

We do have a way of restricting the flow of gasoline in our automobiles. We should be a little more light-footed on our gas pedal. Think of your gas pedal as the flow restrictor for your engine. Those of us who accelerate quickly and brake abruptly are taking long scalding hot showers. You will get far better mileage if you accelerate slowly and if you time your arrival at the traffic lights on Tiburon Boulevard such that you coast to the traffic light without braking. By doing this, you are essentially mimicking the operation of a hybrid vehicle and you will enjoy as much as 20% better fuel efficiency. Also keep your tires fully inflated and keep your trunk empty to avoid schlepping around additional unneeded mass that simply consumes fuel as you accelerate or climb hills.

There is much debate on whether you should fill your tank at night or at midday and whether you are cheated out of some gasoline because of the higher daytime temperature. My view on this is that gasoline is 2% more dense at 50 degrees than it is at 80 degrees so why not fill up early in the morning and gain part of this added mass and also minimize the escape of gasoline vapors from your tank. Certainly in summer months if you choose a gas station that is close to the San Francisco Bay the ground temperature, and hence the gasoline temperature, will be a lot lower than at a gas station in Sonoma. In the summer you will get more pounds of gasoline filling up in Tiburon than in Sonoma if you buy the same number of gallons. In the winter filling up early in the morning in Sonoma would help you gain more pounds of gasoline when purchasing a fixed volume of gallons. Gas stations also typically change their prices at midday. This proves that the early bird does catch the worm if the bird knows where the worm is hiding.