Calculate Thermal Indicated Thermal Efficiency Of An Otto Engine

In summary, the indicated thermal efficiency of an engine is approximately 61.1%, based on the fuel used and heat input calculations. However, this may be slightly lower than the actual efficiency due to possible errors and discrepancies in the data.
  • #1
smokingwheels
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Homework Statement



What is the indicated thermal efficiency of an engine?

Fuel used in total 42.61 cc/min @ 1730 rpm.

Fuel used to get to 1730 rpm = 29.16 cc/min no load.

Fuel left = 13.45 cc/min to do approx 4.335 kw at 1730 rpm approx 40.95 kph

Fuel heat content 34.8 kj/l

Approx 62kj / kw

According to the graph on http://web.mit.edu/16.unified/www/SPRING/thermodynamics/notes/node25.html"
The max ideal engine efficiency is about 62.81% efficient for a compression ratio of 10.5:1 when you look at the bit map with paint.

I worked it out on total fuel and got 36% but the engine uses approx 50% less fuel.
So I used the fuel used to create the power at 1730 rpm.

Homework Equations



Work over heat input.

The Attempt at a Solution



4.335 kw/min = 286 kj

13.45 cc/min = 0.01345 L * 34.8 kj = .46806 Mj = 468 kj

So 286kj / 468 kj = .611 * 100 = 61.1 % indicated thermal efficiency

My test maybe a few % low on consumption when compared to the ADR mileage test which I used the dyno figure for the mass of my car and a 30% efficient drive train.

Note: when I have finished checking and tidying up the raw data it will be in your favor slightly If I have not missed something or made a big error...LOL I wish I had lots of video camera's.

Thanks for all your help so far and in advance People from the Physics Forum.
 
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  • #2
The link to the graph is broken. This makes it hard to figure out if you're right and how to help you if you're not.
 

1. What is the formula for calculating thermal indicated thermal efficiency of an Otto engine?

The formula for calculating thermal indicated thermal efficiency of an Otto engine is:

ηth = (1 - (1 / rγ-1)) x 100

Where ηth represents the thermal efficiency, r is the compression ratio, and γ is the specific heat ratio of the working fluid.

2. How is the thermal indicated thermal efficiency of an Otto engine different from the overall thermal efficiency?

The thermal indicated thermal efficiency of an Otto engine only takes into account the energy produced by the combustion process, while the overall thermal efficiency also considers other factors such as friction, heat loss, and incomplete combustion. Therefore, the thermal indicated thermal efficiency will always be higher than the overall thermal efficiency.

3. What factors affect the thermal indicated thermal efficiency of an Otto engine?

The thermal indicated thermal efficiency of an Otto engine is affected by the compression ratio, specific heat ratio of the working fluid, combustion process, and heat loss. Other factors such as engine design, fuel quality, and operating conditions can also play a role in the efficiency of the engine.

4. How can the thermal indicated thermal efficiency of an Otto engine be improved?

The thermal indicated thermal efficiency of an Otto engine can be improved by increasing the compression ratio, using a higher quality fuel, improving the combustion process, and reducing heat loss through better insulation or engine design. Regular maintenance and proper tuning of the engine can also help improve efficiency.

5. Is the thermal indicated thermal efficiency of an Otto engine the same as its mechanical efficiency?

No, the thermal indicated thermal efficiency and mechanical efficiency are two different measures of an engine's performance. The thermal indicated thermal efficiency focuses on the energy produced by the combustion process, while mechanical efficiency takes into account the energy lost due to friction and other mechanical processes. Therefore, the thermal indicated thermal efficiency is always higher than the mechanical efficiency.

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