With all the hype about hybrid, electric and alternative fuel cars, it's easy to think that the age of the gasoline engine is over. When you've got cars that run on hydrogen or that plug into the wall, the internal combustion engine can seem downright passé.
But the fact remains that the vast majority of cars sold in the United States are powered by gasoline engines. The dominance of gas engines in the automotive market is going to persist for the foreseeable future. Car makers use gasoline engines for a lot of reasons. People are used to them, there's an infrastructure that supports them, and they fit nicely with how most Americans use their cars.
That's not to say that gasoline engines don't have their downsides. They pollute and they're dependent on gasoline -- which leaves American drivers subject to shifts in fuel prices. Though the engine in the car in your driveway has a lot in common with the engines used on the earliest cars, new innovations in engine technology have allowed carmakers to negate some of the problems associated with gasoline automotive engines. Improvements in power, fuel efficiency and emissions are letting people drive the types of cars that they like while also reducing the amount they pollute and the money they spend on gas.
Looking at some of the new technology that improves fuel economy by just a few miles per gallon may not seem like much, but keep in mind that with almost all cars on the road using gasoline engines, small improvements have big impact nationwide. Currently, electric and hybrid cars only make up about 2 percent of the cars on the road. Making the other 98 percent more efficient saves money, reduces dependence on foreign oil and cuts pollution while keeping new cars affordable and appealing to most buyers.
Variable Valve-Timing and Lift
In an engine, the valves open and close to control how the air/fuel mixture enters and how the exhaust exits the combustion chamber. In most gasoline engines, the vales open for the same amount of time and open the same distance regardless of how hard the engine is working. How hard an engine is working is known as its speed. Engine speed doesn't track how fast a car's moving down the road. Instead, engine speed refers to how fast the engine's crankshaft is rotating. That rotation comes from the pistons in the engine's cylinders. The faster they go, the faster the engine speed -- and the harder the engine is working.
Imagine that you're working out really hard. You're going to need lots of fuel, in the form of calories -- and lots of air. You car's engine is the same way, only it uses gas for fuel instead of calories. When you're just ambling along, you don't need as many calories and air. Same with your engine. If the engine valves open for the same amount of time and just as wide regardless of how hard the engine is working, some fuel will get wasted. That's because the engine is getting the same amount of fuel and air whether it's coasting or towing a heavy load.
By varying the time and distance that the valves open, the engine gets just enough fuel and air for the task it's currently performing. In fact, variable valve timing and lift can make a gasoline engine about 5 percent more efficient [source: U.S. Department of Energy].
Cylinder deactivation works on the same principle as variable valve timing and lift: An engine needs different amounts of fuel for different types of work.
Take a V-8 engine, for example. A V-8 engine has eight cylinders. Whenever the engine is on, all eight of those cylinders are working, burning up fuel and air. Most cars, trucks and SUVs with V-8 engines have them because, generally, the more cylinders an engine has, the more powerful it is. That's why you typically see V-8 engines in sports cars or heavy-duty trucks. But, while people like V-8 engines because they go fast and can pull heavy loads, most people aren't doing those things all the time.
That's where cylinder deactivation comes in. Cylinder deactivation shuts down a number of the engine's cylinders when they're not needed. That means that when a car or truck is maintaining a constant speed and not accelerating, some cylinders aren't in use. Since they aren't in use, they aren't getting any gas either -- and that saves fuel. Cylinder deactivation technology has been used on V-8-powered cars and trucks for the past few years, but some car makers are starting to add it to their six-cylinder engines, too. It's estimated that cylinder deactivation technology can improve engine efficiency by 7.5 percent [source: U.S. Department of Energy].
Direct Fuel Injection
Another way gasoline engines are improving is by modifying the way fuel reaches the combustion chamber. In a gasoline engine, fuel and air use a spark to ignite in the combustion chamber. But, researchers have found that by heating and pressurizing the fuel before it's injected into the combustion chamber they can ignite the fuel without a spark -- sort of how a diesel engine operates. This process helps it burn cleaner and more efficiently, reducing the amount of fuel the engine needs to operate.
A normal gasoline engine has a compression ratio of about 10 to 1 (or slightly less). However, a new engine from Mazda (one that is currently on sale in Japan) uses this technology and has a compression ratio of 14 to 1. The Mazda Demio gets a reported 70 miles per gallon (29.8 kilometers per liter).
One problem with an increased compression ratio is that the fuel can ignite prematurely, causing what's known as engine knock. To help keep that from happening, direct injection systems spray a fine mist of fuel directly into the cylinder (usually, air and fuel are mixed in the port before entering the system). That helps keep the engine's temperature down and reduces knock. Direct fuel injection can improve engine efficiency by 12 percent [source: U.S. Department of Energy].
Turbochargers are fans powered by gasses from the car's exhaust system. They allow more compressed air to go into the cylinder. That allows for a higher compressions ratio (just like direct fuel injection), and therefore, more efficient combustion. Think of a turbocharger as direct injection for the air part of an engine's air/fuel mixture.
While using a turbocharger allows performance cars to generate even more power, putting them on a smaller engine allows them to do the same work as a bigger engine -- and that saves fuel. In 2011, Ford added a turbocharged V-6 engine to its line of engines for its F-150 trucks. Called EcoBoost engines, they prove that you don't need a V-8 in a pickup. With a turbocharger, the EcoBoost engine in the 2011 F-150 makes 365 horsepower, 420 pound-feet of torque and can tow up to 11,300 pounds (5,126 kilograms). By comparison, the base V-8 in the F-150 makes 360 horsepower and 380 pound-feet of torque. The EcoBoost V-6 in the F-150 not only makes more power, it also gets better fuel economy than the V-8. In two-wheel drive, the EPA says it gets 16/22 miles per gallon (6.8/9.4 kilometers per liter) city/highway, while the base V-8 gets 15/21 miles per gallon (6.4/8.9 kilometers per liter) city/highway.
The biggest variable in how much gas an engine uses isn't completely in its technology. It's in how it's driven. It's simple, really: Floor the accelerator and you're going to use more gas than someone who accelerates gradually. There's a reason fuel economy estimates always note that your mileage may vary.
But, car companies are finding ways to train drivers to drive more efficiently. By letting the driver know when they're driving efficiently, the engine can spend more time operating at levels where efficiency is optimized. For example, the Kia Forte and the 2011 Honda Odyssey have green lights on the dashboard that indicate when they're being driven efficiently. And they're not the only ones -- several carmakers have similar driver efficiency indicators. The manufacturers hope that drivers will treat keeping the efficiency light on as a sort of game, increasing their overall efficiency and decreasing fuel consumption.
Another feature that many new cars have is something called eco mode. While eco modes are common on hybrids, automakers are beginning to add them to gasoline-only cars as well. In most cars, eco mode is activated by pushing a button. That changes the transmission shifting characteristics to keep the engine operating at lower speeds. Since the engine isn't working as hard, it doesn't use as much fuel. Though eco mode doesn't work in all driving situations (it can provide some lag on the highway, for instance), for around town driving it can definitely help you use less gas.
For more information about new gasoline engine technologies and other related topics, follow the links on the next page.
Is it possible for something as simple as new motor mounts to increase engine response in your car or truck? Find out at HowStuffWorks.
- Bullis, Kevin. "70 MPG without a Hybrid." Technology Review. Oct. 25, 2010. (May 16, 2011) http://www.technologyreview.com/energy/26613
- Bullis, Kevin. "Hydrogen Reality Check." Technology Review. May 5, 2006. (May 16, 2011) http://www.technologyreview.com/energy/16777/page1/
- Carney, Dan. "Ford's EcoBoost F-150 Packs a Powerful Punch." MSNBC. Nov. 5, 2010. (May 16, 2011) http://www.msnbc.msn.com/id/39969898/ns/business-autos/t/fords- ecoboost-f--packs-powerful-punch/
- Mays, Kelsey. "More Details on Chevy Equinox's Eco Mode." Kicking Tires. June 29, 2009. (May 16, 2011) http://blogs.cars.com/kickingtires/2009/06/chevrolet-equinox.html
- U.S. Department of Energy. "Energy Efficient Technologies." U.S. Department of Energy and Environmental Protection Agency. (May 16, 2011)http://www.fueleconomy.gov/feg/tech_adv.shtml