Internal combustion engines: where does all that wasted heat go?
(NC)—The majority of vehicles on the road today are powered by internal combustion engines. These engines generate power by burning fuel and air in the engine cylinder, which when ignited, creates the energy that pushes the piston to propel the vehicle forward.
Sounds great except internal combustion engines are extremely inefficient at converting the chemical energy of fuel into forward motion; in fact, from a cup and a half of gasoline (the equivalent of a can of pop or about 355 millilitres) most vehicles will only use about four tablespoons (60 millilitres) to move the vehicle forward and power the electrical system. The rest of the fuel is lost through heat, idling, friction, incomplete combustion and other inefficiencies associated with internal combustion engines; in fact, only about 16 percent of the energy is used to actually move the vehicle while the remaining 84 percent is lost to those various other factors.
Here's a breakdown:
Engine losses – 65 percent. Losses occur from engine friction, pumping air into and out of the engine, and wasted heat, which is the largest component of engine energy losses.
Idling - 11 percent. Idling occurs mostly during urban driving, while the vehicle remains stationary at intersections or in congested traffic. Remember, the amount of fuel you use during 10 seconds of idling is the amount it takes to restart your engine.
Drivetrain - 5.5 percent. The drivetrain transfers energy from the engine to the wheels through several components, including the driveshaft, transmission, differential and axle. Energy losses occur due to friction in the gears and bearings.
Accessories - 1.9 percent. The belts and chains connected to the engine's crankshaft draw continuous power, even when the accessories are not in use, which results in wasted fuel.
Inertia - 4.2 percent. The energy needed to move the vehicle is determined mainly by its weight. The heavier a vehicle is, the more inertia it has and the more energy is required to accelerate or to brake.
Rolling resistance - 5.5 percent. Rolling resistance is friction between the tires and the road. As a vehicle travels, its weight deforms the tire tread where the tire contacts the road. This deformation generates heat between the tire and the road, which is then lost to the surrounding atmosphere. The power required to overcome rolling resistance increases with speed.
Aerodynamic drag - 6.3 percent. Aerodynamic drag is caused by friction between the moving vehicle's surface and the air. Drag forces are minimal at low speeds, but become much stronger at higher speeds.
So what does all this mean for you the buyer?
It means looking for the most fuel-efficient vehicles you can afford. According to Natural Resources Canada, over 10 years, a 20 to 35 percent reduction in fuel consumption for 20,000 km/year of combined city and highway driving can result in fuel savings ranging from $3,500 to $13,100 and potential CO2 reductions ranging from 6,400 to 24,200 kg.
It's food for thought that is definitely worth digesting. You can learn more about fuel efficiency at www.vehicles.nrcan.gc.ca.
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