What are the different types of power losses in a car engine?

In summary, power loss in a car engine to the wheels varies with engine speeds and is dependent on the type and manufacturing tolerances of the engine and transmission system. The power loss is made up of various factors such as air drag, windage losses, frictional losses in bearings and gears, and the number of gears in the transmission. The estimate of 12% of fuel energy being delivered to the wheels is likely optimistic and can vary between different types and units of the same type. The power loss due to air drag is proportional to the cube of the vehicle's speed.
  • #1
Max90
2
0
Hello, i would like to know in what ways power is loss from a car engine to the wheels and what are the percentages of the power losses that occur.
Do the power losses vary with engine speeds?
Also, how much power does the electric motor starter consume?

Max90
 
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  • #2
welcome
power varies with RPM...so the power loss thru parasitic drag og transmission/differential would also vary. the amount is engine/ trans/diff dependent.
starter motor takes minimal electric power to turn over engine and this is replaced via alternator
 
  • #3
I know that power loss due to air drag is proportional to the square of vehicle's speed.
I have read somewhere that for a gasoline engine, "of the 25 percent crankshaft power, about 4 percent is used up by accessories, 9 percent by friction and slippage in the mechanical systems (transmission and differential), leaving only about 12 percent of the fuel energy to be delivered to the wheels".
How does the power loss associated with trans/diff vary with engine speeds? Will it simply increase?

Max90
 
  • #4
Asking how much powerloss comes from an engine is like asking what colour are pencil crayons?

The power output and losses of an engine and transmission system, will not only vary between types (can vary a great deal) but also between units of the same typre due to manufacturing tolerances.

12% seems a very low estimate, even for poor engines.
 
  • #5
Max90 said:
I know that power loss due to air drag is proportional to the square of vehicle's speed.
Max90

Proportional to the cube of the vehicle's speed.

As has been said, power lost in the drivetrain is not so easy to figure out. There's windage losses (the gears, engine swinging through the oil/ oil mist) that will obviously rise with rpm, but not necessarily load. There's frictional losses in bearings and gears that will rise with rpm and load.

Each gear, each bearing, each moving part takes up a certain small percentage of the total power. The more gears (such as in 4wd and rear-wheel drive cars), the more power lost. An automatic transmission usually gives more power loss.

Good luck figuring out each individual component. The 12% mentioned is an easier way to estimate it, although it's probably being very optimistic. I've heard around 15% of power for front-wheel drive cars...
 

FAQ: What are the different types of power losses in a car engine?

What causes power losses in automobiles?

Power losses in automobiles can be caused by a variety of factors, including friction in the engine and drivetrain, inefficient fuel combustion, and resistance in the electrical system. These losses can lead to decreased engine performance and reduced fuel efficiency.

How do I know if my car is experiencing power loss?

Some signs that your car is experiencing power loss include a decrease in acceleration and top speed, difficulty starting the engine, and lower fuel efficiency. You may also notice strange noises or vibrations coming from the engine.

Can power losses be prevented?

While some losses are inevitable due to the nature of engine mechanics, there are steps you can take to minimize power losses. Regular maintenance, such as changing the oil and air filters, can help keep your engine running smoothly. Additionally, using high-quality fuel and keeping your tires properly inflated can improve fuel efficiency and reduce friction in the drivetrain.

How does driving style affect power losses?

Aggressive driving, such as rapid acceleration and braking, can increase power losses in your car. This is because sudden changes in speed require more fuel and put extra strain on the engine and drivetrain. By driving more smoothly and steadily, you can reduce power losses and improve fuel efficiency.

Are there ways to recover power losses in my car?

In some cases, power losses can be recovered through repairs or upgrades. For example, replacing worn spark plugs or using a higher grade of motor oil can improve engine performance and reduce power losses. However, it is important to consult a qualified mechanic before making any changes to your car's engine or electrical system.

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