Engine Efficiency and Fuel Savings

Automobile Engine Efficiency

Engine efficiency is the percentage of chemical energy in a fuel that is converted into mechanical energy to move a car down the road. The latest gasoline engines are commonly just 25 to 35 percent efficient, while diesel engines are a bit better with typical efficiencies in the mid-to-upper 30s. These numbers leave lots of room for improvement, and automakers are devoting extensive resources to increase engine efficiency to help meet EPA fuel economy standards.

Technologies now in production include engines with Diesel and Atkinson combustion cycles, engine stop-start systems, cylinder deactivation, higher compression ratios, smaller displacement engines, turbocharging, low-rpm operation, variable valve timing and lift, gasoline direct injection and various methods to reduce engine accessory loads and internal friction.

Avenues being explored to increase future engine efficiency include low-temperature, lean-burn and clean-diesel combustion, along with co-optimization of engines and fuels, camless valvetrains, waste heat recovery and laser/plasma ignition systems.

The more efficient engines of today and tomorrow provide better fuel economy and reduced exhaust emissions, but many also have maintenance requirements such as the use of semi- or full-synthetic oils that must be followed to ensure proper engine operation and maintain warranty coverage.

Maximizing Vehicle Efficiency

More than half the gasoline or diesel you pump into your car goes to waste. That’s right, roughly 60 cents out of every dollar you spend on fuel does absolutely nothing to move your car down the road. Why? Because internal combustion automobile engines are simply not very efficient.

Where does the rest of the fuel energy go? A small amount powers engine accessories such as the air conditioning compressor, water pump and alternator. However, more than half is thrown away as waste heat through the engine cooling and exhaust systems. And more is lost to internal friction, intake and exhaust restrictions, and incomplete combustion.

If you want to purchase a vehicle that offers maximum efficiency, the easiest way is to consider those models that have the highest EPA estimated fuel economy ratings. If you do extensive urban driving, you may also want to seek out a model with a stop-start system that shuts down the engine when the car is stopped in traffic. While the operation of these systems may seem unusual at first, they can deliver meaningful efficiency gains.

Finally, when seeking optimum efficiency, don’t overlook your own driving behavior; it has a major effect on fuel economy. Moderate acceleration at low rpms, staying within the speed limits, coasting down to stopped traffic, gentle braking when necessary, and “driving ahead” to eliminate unnecessary acceleration and “time” traffic lights are all proven practices to maximize fuel efficiency.