Energy Losses in a typical Gasoline Vehicle

Only about 15% of the energy from the fuel you put in your tank is used to move your car down the road or run useful accessories, such as air conditioning. The rest of the energy is lost to engine and driveline inefficiencies and idling. Therefore, the potential to improve fuel efficiency with advanced technologies is enormous.

Source: U.S. Dept. of Energy

Engine Losses – 62.4 percent
In gasoline-powered vehicles, over 62 percent of the fuel’s energy is lost in the internal combustion engine (ICE). ICE engines are very inefficient at converting the fuel’s chemical energy to mechanical energy, losing energy to engine friction, pumping air into and out of the engine, and wasted heat.

Advanced engine technologies such as variable valve timing and lift, turbo charging, direct fuel injection, and cylinder deactivation can be used to reduce these losses.

In addition, diesels are about 30-35 percent more efficient than gasoline engines, and new advances in diesel technologies and fuels are making these vehicles more attractive.

Idling Losses – 17.2 percent
In urban driving, significant energy is lost to idling at stop lights or in traffic. Technologies such as Start Stop systems help reduce these losses by automatically turning the engine off when the vehicle comes to a stop and restarting it instantaneously when the accelerator is pressed.

Accessories – 2.2 percent
Air conditioning, power steering, windshield wipers, and other accessories use energy generated from the engine. Fuel economy improvements of up to 1 percent may be achievable with more efficient alternator systems and power steering pumps.

Driveline Losses – 5.6 percent
Energy is lost in the transmission and other parts of the driveline. Technologies, such as automated manual transmission and continuously variable transmission, are being developed to reduce these losses.

Aerodynamic Drag – 2.6 percent
A vehicle must expend energy to move air out of the way as it goes down the road,less energy at lower speeds and progressively more as speed increases. Drag is directly related to the vehicle’s shape. Smoother vehicle shapes have already reduced drag significantly, but further reductions of 20-30 percent are possible.

Rolling Resistance – 4.2 percent
Rolling resistance is a measure of the force necessary to move the tire forward and is directly proportional to the weight of the load supported by the tire. A variety of new technologies can be used to reduce rolling resistance, including improved tire tread and shoulder designs and materials used in the tire belt and traction surfaces.

For passenger cars, a 5-7 percent reduction in rolling resistance increases fuel efficiency by 1 percent. However, these improvements must be balanced against traction, durabillity, and noise.

Overcoming Inertia; Braking Losses – 5.8 percent
To move forward, a vehicle’s drivetrain must provide enough energy to overcome the vehicle’s inertia, which is directly related to its weight. The less a vehicle weighs, the less energy it takes to move it. Weight can be reduced by using lightweight materials and lighter-weight technologies (e.g., automated manual transmissions weigh less than conventional automatics).

In addition, any time you use your brakes, energy initially used to overcome inertia is lost.

Type of Losses

We can divide these vehicular losses into three basic types as follows:

Friction
Wind resistance, rolling resistance, mechanical friction (two parts moving against each other), and hydraulic friction (force required to push or pump a liquid)

Mechanical Load
The combination of losses incurred by the engine due to powering accessories such as air conditioning, electrical, and power steering as well as vehicle weight and payload

Heat & Noise
loss of energy in theform of heat loss or vibrational noise

Tips and Techniques for Reducing Friction Losses

Tip #1 Keep your tires inflated properly
Make sure to check your tire pressure any time there is a change in temperature outside and keep them filled up near the highest pressure listed on the tire. It’s good practice to check them every week. This may be one of the most important ways for you to keep your fuel mileage high. Remember, adjusting your tire pressure for your specific vehicle load is important for optimum fuel mileage. Both safety and efficiency are clearly at risk if this is not proper.

Check for abnormal wear, typically along the center line of the tire if over-inflated and along the edges if under-inflated. Uneven wear or cupping of the tread along one or both edges is an indication of an alignment problem or an issue with your shocks or struts.

Tip #2 Don’t drive with your windows down
In general experts suggest driving without Air Conditioning unless you really need it. There is a trade-off here. If it is too warm to keep the A/C off and keep your windows up, you are better off running your A/C than you are driving with at highway speeds with your windows down because of the excessive drag created by the open windows.

Tip #3 Apply synthetic bearing grease to your wheel bearings
Good quality synthetic bearing grease will greatly reduce the friction around your wheel bearings and will help decrease overall rolling resistance.

Tip #4 Use synthetic oil in your transmission, differential and transfer case
Good quality synthetic ATF or appropriate gear oil will dramatically reduce the friction and operating temperature inside your automatic or manual transmission, differential(s) or transfer case. It could also last up to 50,000 miles, or 3 to 5 times longer than conventional petroleum based oils.

Tip #5 Make sure your wheels are aligned to reduce rolling resistance
Maintaining your vehicle’s alignment is paramount to the operational efficiency and safety of your vehicle. It should be in alignment and as level and straight as the level road you are traveling down. If you have a “cantered” steering wheel while driving straight down the road, you are probably in need of an alignment

Many times you might have bumped a curb or hit a pretty significant bump. Even one small uneventful bump from a curb can significantly mis-align your car.

It can also cause premature wearing of your tires. This can be a double whammy in that you pay more out of your pocket for each inch you travel because of poor mileage caused by an out of alignment vehicle AND having to buy new tires more often. Sounds a bit simplistic but this is a commonly overlooked mileage eater.

Tip #6 Maintain your brakes and make sure your emergency brake is disengaged
There are two parts to the brake equation – your standard brakes and your emergency brakes. Both are absolute critical systems and the highest priority should be given to their maintenance and effectiveness.

The worn and improperly maintained brakes can cause excess drag and may become a driving hazard. The brake pad contact points can fall out of alignment, ever so slightly, and create unwanted friction between the pads and the rotors. In most cases, you will hear a slight chatter or chirp telling you there is a problem. You may also feel this as slight vibration or chatter with your foot as you apply pressure on the brakes. Additionally, today’s newer cars, with 4- wheel disc brakes, have a second-set of brake shoes (emergency brakes), used to keep the car from rolling when parked and to stop the car in the event the primary system has failed.

All too many times drivers leave the parking brake partially engaged and do not figure this out until they see smoke. If the emergency brakes get so hot they begin to fuse the shoe to the friction material it is in contact with, you may feel a distinct chatter or vibration in the car.

Tip #7 Make your vehicle more aerodynamic
Anything attached to the outside of your vehicle will add extra wind resistance. A car-top carrier, a bike rack on the back, even your luggage rack will add wind resistance. If your luggage rack is removable, take it off when you don’t need it.

If you can add an air dam, spoilers, or fairings around the bottom of the vehicle to minimize the amount of air that can pass underneath, the vehicle will be more aerodynamic and the engine won’t need to work so hard to move it. Obviously, if you truly go off-road in your SUV or truck then this may not be the option for you.