Why compression ratio of petrol engine is smaller than diesel engine?
Due to its high flash point it is relatively safer than petrol. Therefore diesel can be ignited by heat generated by compression of air inside a cylinder which requires higher compression ratio whereas a petrol engine uses spark ignition and hence has lower compression ratio.
Why is Otto cycle more efficient than Diesel cycle for the same compression ratio and heat input in Otto cycle?
Otto cycle efficiency is higher than Diesel cycle efficiency for the same compression ratio and heat input because, in Otto cycle. Combustion is at constant volume.
What is the primary reason why an Otto cycle is less efficient than a Carnot cycle?
The cylinders are not perfectly insulated from the engine block, so heat energy is lost from each cylinder by conduction. This makes the engine less efficient that a Carnot engine, because heat is being discharged at a temperature that is not as cool as the environment.
Why is there a limit to the compression ratio for an Otto engine?
In ordinary gasoline engines, the compression ratio has its limits. Since the temperature attained by the fuel-air mixture during the compression increases as the compression ratio increases, the likelihood of autoignition increases with the compression ratio.
Why the compression ratio of diesel engine is usually greater than petrol cycle?
Diesel engines use higher compression ratios than petrol engines, because the lack of a spark plug means that the compression ratio must increase the temperature of the air in the cylinder sufficiently to ignite the diesel using compression ignition.
Why is higher compression ratio better?
A higher compression ratio (CR) is beneficial for engines. That’s because the higher ratio allows for an engine to extract more energy from the combustion process due to better thermal efficiency. Higher compression ratios allow the same combustion temperatures to be achieved with less fuel.
Why the higher efficiency of the Otto cycle compared to diesel cycle for the same compression ratio is only of academic interest and not practical importance?
3. 6 Diesel Cycle. Although for a given compression ratio the Otto cycle has higher efficiency, because the Diesel engine can be operated to higher compression ratio, the engine can actually have higher efficiency than an Otto cycle when both are operated at compression ratios that might be achieved in practice.
Why the higher efficiency of the Otto cycle compared to the diesel cycle?
A diesel cycle can operate with a higher compression ratio than an Otto cycle as there is no risk of auto-ignition of the fuel and only air is compressed. But, for a given compression ratio, the Otto cycle has higher efficiency than the diesel engine.
What is the relation between compression ratio and the efficiency of the Otto cycle?
Explanation: This is the expression for efficiency of Otto cycle and rk=compression ratio=Vmax/Vmin.
What is the relation between compression ratio and the efficiency of the Otto cycle Mcq?
Important Points
| C.I.Engine | S.I.Engine |
|---|---|
| compression ratio: 16:1 to 22:1 | compression ratio: 6:1 to 12:1 |
| Thermal efficiency is high. | Thermal efficiency is less. |
| Weight per unit power is more. | Weight per unit power is less. |
| Produce high torque and operating speed is less. | Produce less torque but operating speed is quite high. |
Why is Otto cycle more efficient?
Although for a given compression ratio the Otto cycle has higher efficiency, because the Diesel engine can be operated to higher compression ratio, the engine can actually have higher efficiency than an Otto cycle when both are operated at compression ratios that might be achieved in practice.
Is a lower compression ratio better?
Compression ratios usually range from 8:1 to 10:1. A higher compression ratio — say, from 12:1 to 14:1 — means higher combustion efficiency. Higher compression ratios and combustion efficiency mean more power with less fuel, and fewer exhaust gases.