At The Pumps: Your Car's Fuel Requirements

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Knowing the right fuel for your car is essential.

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While we may not have reached the point where we can power a time-traveling DeLorean with banana peels, you do have more options when it comes to fuel for your car than you did 36 years ago. Fossil fuel may still be the staple in many countries around the globe, but governments and automakers are doing their best to move away from this quickly dwindling resource as different types of car fuel are made available, each offering their own specific benefits. In this guide, we discuss the various alternatives and everything you need to know about what goes into your car's engine.

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What is Fuel?

Almost all types of car fuel are derived from crude oil, natural gas, or biomass. Production entails breaking down the crude oil into components or fractions in a distillation process. By heating the oil, vapor is produced, which is then cooled and the condensed product is collected at different heights and temperatures, as per the diagram below.

In the case of gasoline, different petroleum products from the various refining processes are combined to create base gasoline for regular and premium grades. Most of the finished types of gasoline for cars in the USA contain about 10% fuel ethanol. This is significant in that this meets the requirements of the Renewable Fuel Standard, which aims to reduce greenhouse gas emissions through various required standards for the composition of transportation fuel sold in the US. There are three main grades of gasoline sold in the US, named for their octane rating:

  • Regular
  • Midgrade
  • Premium
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Types of Car Fuel

Each car engine is designed to run on a specific type of fuel. The same goes for the system that supplies fuel to the engine - it must be able to withstand the chemistry of the fuel. A list of the most common car fuel types currently in use include:

  • Gasoline is most widely used in the US for light-duty vehicles like cars and pickup trucks. In most parts of the US, common grades of gas for cars are noted as follows: regular gasoline is 87 octane, mid-grade is 89 and premium is 91, 92, or 93. In areas at high altitudes where the air contains less oxygen to support combustion, regular, mid-grade, and premium gasoline are usually 85, 87, and 91, respectively.
  • Diesel is derived from petroleum and has a higher mass density than gasoline, meaning that diesel fuel contains more energy than the same volume of gasoline. Because of diesel's higher mass density and the engine's higher compression ratio, diesel-fuel cars are more energy efficient. One major drawback, however, is that diesel produces more harmful emissions.
  • Biodiesel is made from renewable resources like vegetable and grain oils, tallow, and lard, as well as from biomass such as algae. Biodiesel cars produce lower net emissions than regular diesel. It is generally blended with petrodiesel in varying percentages; pure biodiesel fuel is known as B100 (100% biodiesel). A biodiesel to petrodiesel ratio of 20:80 (B20) is considered the optimum blend as fuel for cars. It is utilized by some state and federal government agencies with fleets, and is popular in the trucking industry for its excellent lubricating properties. Medium or heavy trucks and buses are also using more biodiesel, especially in areas where air quality is a concern. Biodiesel usage in the USA has grown in the last few years; as per volumes reported under the Renewable Fuel Standard (RFS), usage has increased from 2.89B gallons in 2016 to 3B gallons in 2020.
  • Hydrogen fuel is used to generate electricity, so a hydrogen fuel-cell car is actually an electric car that has replaced its battery with a chemical process that produces electricity for the motors and car systems. This setup is far more efficient than an internal combustion engine, with steam or distilled water being the only byproduct. However, it is more costly and these cars usually have a higher starting price as a result. Additionally, there are very limited fueling station options available at present.
  • Ethanol is the most common biofuel in the US - it's made from biomass that includes grains and crops with a high sugar or starch content. Regular gasoline for cars is commonly blended with ethanol in a 9:1 ratio called E10. However, E85, also known as flex-fuel, which has an 83% ethanol content, is also popular. Fuels with an ethanol content of more than 15 percent can only be used in 'flex-fuel' vehicles with specialized equipment since ethanol fuel for cars is corrosive.
  • Liquefied Petroleum Gas (LPG) is a mixture of propane and butane and is not particularly expensive. And while it does not result in a drop in performance, fuel economy is typically lower than conventionally-fuelled vehicles. Advantages include longer engine life, fewer oil services, reduced emissions, and better spark plug life. However, a drawback to LPG is the limited number of fuel stations that carry it.
  • Compressed Natural Gas (CNG) is a natural gas and can be converted to liquid as liquefied natural gas (LNG), too. It isn't too difficult to convert gasoline-powered vehicles into CNG-fuel cars. These emit 5-10% less carbon dioxide (CO2) than gas-fed variants. Like LPG, there are a limited number of fuel stations that carry this type of fuel, making these vehicles most practical for centrally-fueled fleets.
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Fuel Type Comparisons

Is any one fuel type better than the rest? Some are certainly better-suited to certain circumstances. Here is a breakdown of which fares best:

Gasoline vs. Diesel

Diesel's higher energy per volume compared with gasoline, plus a higher engine compression ratio, means diesel-fuel cars give better mpg estimates. While regular gas and diesel generally cost about the same, you get more out of the same amount of diesel in a tank in terms of mileage. However, diesel soot and emissions remain a concern.

Regular vs. Premium

The key difference between regular and premium gasoline is octane, which is the ability of the fuel to combust at the correct time; mistimed ignition is called pre-ignition or knocking. Higher octane gasoline resists pre-ignition better, which is why performance engines often recommend using premium fuel to prevent damage to the engine. Be sure to read more on this subject here.

Alternative Fuels

Is there a big difference between cars that run on CNG or LPG fuel? Is one more efficient than the other? Not really. They are not interchangeable, but when choosing a vehicle or converting your existing vehicle, your choice should be based on the availability of each fuel in your area, and how each one affects the environment as it exits the exhaust pipe. Neither are currently widely available across the States, so do your research first. In terms of emissions, both are better than standard gasoline engines, but biodiesel is slightly better for the environment. Although hydrogen fuel vehicles are by far the most environmentally friendly, they are expensive and only a small group of manufacturers produce them.

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What Goes Into Making a Good Fuel?

With all these options to choose from, what are the qualities that make a fuel good for the average Joe? The ideal fuel should tick every box in terms of efficiency, environmental friendliness, low cost, and performance, but this is not entirely realistic. Nevertheless, here is a checklist for choosing the best fuel:

  • A good fuel should not be cheap to fill up with and offer superior mileage figures.
  • It should be readily available, meaning you should be able to top up with relative ease.
  • Engine emissions should not be harmful to the environment.
  • It must provide enough power to the engine.

FAQs

How is fuel economy calculated?

Fuel economy refers to the distance a car can travel using a specific amount of fuel. In the US, this is expressed as miles per gallon (mpg). The Environmental Protection Agency (EPA) derives fuel economy through lab-controlled tests, but you can estimate your mpg by dividing the distance traveled between tank refills by the amount of fuel your tank can hold.

Which cars are most fuel-efficient?

In terms of running costs, EVs are definitely the most economical cars, though they cost a bit more to buy outright. However, vehicles that utilize regular gasoline, diesel, or alternative fuels can still be fuel efficient, too. Of the various types of fuels mentioned here, fuel cell vehicles like the Honda Clarity, Hyundai Nexo, and the Toyota Mirai offer superb EPA estimates, with mileage figures for each working out to 68, 61, and 74 MPGe in combined cycles, respectively.

Can an SUV or truck offer good gas mileage?

Yes. Gone are the days where an SUV with a 3rd row would cost a fortune to drive regularly. Many manufacturers now offer SUVs and pickups as hybridized variants. Some of the most fuel-efficient SUVs include the Kia Sorento Hybrid, Toyota RAV4 Hybrid/Prime, and Toyota Venza. Trucks that offer impressive fuel consumption ratings, albeit gas/diesel-fed include the Ram 1500 diesel and the Toyota Tacoma.

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