physics

Miles per gallon gasoline equivalent

Miles per gallon gasoline equivalent is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Miles per gallon gasoline equivalent rather than just read about it. In short: Miles per gallon gasoline equivalent (MPGe or MPGge) is a measure of the average distance traveled per unit of energy consumed. MPGe is used by the United States Environmental Protection Agency (EPA) to compare energy consumption of alternative fuel vehicles, plug-in electric vehicles and other advanced technology vehicles with the energy consumption of conventional internal combustion vehicles rated in miles per U…

Key takeaways

Miles per gallon gasoline equivalent belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Miles per gallon gasoline equivalent to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Miles per gallon gasoline equivalent from memory before moving on to harder problems.

Reference excerpt

Miles per gallon gasoline equivalent (MPGe or MPGge) is a measure of the average distance traveled per unit of energy consumed. MPGe is used by the United States Environmental Protection Agency (EPA) to compare energy consumption of alternative fuel vehicles, plug-in electric vehicles and other advanced technology vehicles with the energy consumption of conventional internal combustion vehicles rated in miles per U.S. gallon. The unit of energy consumed is deemed to be 33.7 kilowatt-hours without regard to the efficiency of conversion of heat energy into electrical energy, also measured in kilowatt-hours (kWh). MPGe does not necessarily represent an equivalency in the operating costs between alternative fuel vehicles and the MPG rating of internal combustion engine vehicles due to the wide variation in costs for the fuel sources regionally since the EPA assumes prices that represents the national averages. Miles per gallon equivalent cost for alternate fuel can be calculated with a simple conversion to the conventional mpg (miles per gallon, miles/gal). See conversion to MPG by cost below. The MPGe metric was introduced in November 2010 by EPA in the Monroney sticker of the Nissan Leaf electric car and the Chevrolet Volt plug-in hybrid. The ratings are based on EPA's formula, in which 33.7 kWh (121 MJ) of electricity is equivalent to one (U.S.) gallon of gasoline, and the energy consumption of each vehicle during EPA's five standard drive cycle tests simulating varying driving conditions. All new cars and light-duty trucks sold in the U.S. are required to have this label showing the EPA's estimate of fuel economy of the vehicle. In a joint ruling issued in May 2011 the National Highway Traffic Safety Administration (NHTSA) and EPA established the new requirements for a fuel economy and environment label that is mandatory for all new passenger cars and trucks starting with model year 2013. This ruling uses miles per gallon gasoline equivalent for all fuel and advanced technology vehicles available in the U.S. market including plug-in hybrids, electric vehicles, flexible-fuel vehicles, hydrogen fuel cell vehicle, natural gas vehicles, diesel-powered vehicles, and gasoline-powered vehicles. In addition to being displayed on new vehicles, fuel economy ratings are used by the U.S. Department of Energy (DOE) to publish the annual Fuel Economy Guide; the U.S. Department of Transportation (DOT) to administer the Corporate Average Fuel Economy (CAFE) program; and the Internal Revenue Service (IRS) to collect gas guzzler taxes. Fuel economy estimates for window stickers and CAFE standard compliance are different. The EPA MPGe rating shown in the Monroney label is based on the consumption of the on-board energy content stored in the fuel tank or in the vehicle's battery, or any other energy source, and only represents the tank-to-wheel energy consumption. CAFE estimates are based on a well-to-wheel basis and in the case of liquid fuels and electric drive vehicles also account for the energy consumed upstream to produce the fuel or electricity and deliver it to the vehicle. Fuel economy for CAFE purposes include an incentive adjustment for alternative fuel vehicles and plug-in electric vehicles which results in higher MPGe than those estimated for window stickers.

Background

1988: Alternative Motor Fuels Act The Alternative Motor Fuels Act (AMFA) enacted in 1988 provides Corporate Average Fuel Economy (CAFE) incentives for manufacturing alternative fuel vehicles (AFVs) that are powered by ethanol, methanol, or natural gas fuels, either exclusively or in conjunction with gasoline or diesel fuel. These dual-fuel vehicles also are known as flexible-fuel vehicles (FFVs). To provide incentives for the widespread use of these fuels and to promote the production of AFVs and FFVs, AMFA grants AFV/FFV manufacturers CAFE credits, which allows them to raise their overall fleet fuel economy levels to comply with the CAFE standards. Beginning in 1993, manufacturers of qualified AFVs can improve their CAFE estimation by computing the weighted average of the fuel economy when operating on conventional fuel (gasoline and diesel) and when operating on alternative fuel(s). AMFA provides the following energy content-based equivalency factors:

1 gal (alcohol) = 0.15 gal (gasoline) 100 ft3 (natural gas) = 0.823 gal-equivalent (natural gas) 1 gal-equivalent (natural gas) = 0.15 gal (gasoline) A dedicated AFV which operates solely on alcohol would divide the alcohol fuel economy by the energy-equivalency factor of 0.15. As an example, a dedicated AFV that achieves 15 mpg fuel economy while operating on alcohol would have a CAFE calculated as follows:

F E a l c o h o l = 1 0.15 ⋅ ( 15 m p g a l c ) = 100 m p g e q u i v {\displaystyle FE_{alcohol}={\frac {1}{0.15}}\cdot (15\,mpg_{alc})=100\,mpg_{equiv}}

For FFVs, an assumption is made that the vehicles would operate 50% of the time on the alternative fuel and 50% of the time on conventional fuel, resulting in a fuel economy that is based on a harmonic average of alternative fuel and conventional fuel. For example, for an alternative dual-fuel model that achieves 15 miles per gallon operating on an alcohol fuel and 25 mpg on the conventional fuel, the resulting CAFE would be:

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Miles per gallon gasoline equivalent

Start with the simplest possible case. Write down what Miles per gallon gasoline equivalent claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Miles per gallon gasoline equivalent before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Miles per gallon gasoline equivalent ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Miles per gallon gasoline equivalent

In research: Miles per gallon gasoline equivalent appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Miles per gallon gasoline equivalent in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Miles per gallon gasoline equivalent is common in secondary-school and first-year university syllabi. It links to neighbouring topics Car costs, Energy conservation, Energy economics, so understanding it makes those chapters shorter.
In everyday life: Look for Miles per gallon gasoline equivalent outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Miles per gallon gasoline equivalent in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Miles per gallon gasoline equivalent means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Miles per gallon gasoline equivalent out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Miles per gallon gasoline equivalent in simple terms?

Why does Miles per gallon gasoline equivalent matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Miles per gallon gasoline equivalent?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Miles per gallon gasoline equivalent.