To increase the output of a spark-ignition engine by either
- raising the compression ratio from 8 to 10
(2) increasing the inlet pressure from 1.0 atm to 1.5 atm. Using the constant-volume cycle (Otto cycle) as a model for engine operation
which procedure will give?
- The highest pressure?
Highest pressure is assumed to be Ps
Ps=(r=8, P1=1.0)=66.1 atm
Ps=(r=8, P1=1.3)=94 atm
Ps=(r=8, P1=1.5)= 118.98 atm
- The highest efficiency?
Efficiency is therefore a function of compensation ration (r) and so a higher compensation ratio result in high efficiency
r=10 implies highest efficiency
- The highest mean effective pressure (mep)?
Imep=(r=8, P=1.0) =13.13 atm
Imep=(r=9, P=1.3) =14.34 atm
Imep=(r=10, P=1.5) =23.64 atm
The best method to obtain the highest output of the spark ignition combision engine is by varying both the value of pressure and the compensation ration.
In this case, the highest mean effective pressure is obtained at the compensation ratio of 10 and at a pressure of 1.5 Pascal
- How would one increase the compression ratio and the inlet pressure in an internal combustion engine?
The compression ratio is the ratio between the volume of the gas in a internal combustion cylinder when the valve is at the top and when at the bottom. For instance, a combustion chamber with 1000cc reduces to 100cc when the pistol is at the top is said to have a compression ratio of 1000:100 or 10:1. Compression ratio can therefore be said to be the expansion ratio. A high compression ratio is desired and can be obtained by using elastic cylinder that will not increase the temperature with increase in pressure. As a result, less heat will be emitted into the surrounding.
Djouadi, Amel and Fatiha Bentahar. 2016. “Combustion Study Of A Spark-Ignition Engine From Pressure Cycles”. Energy 101: 211-217. doi:10.1016/j.energy.2016.02.013.
Panua, Raj Sekhar and Biswajit De. 2014. “OPTIMIZATION OF COMPRESSION RATIO OF JATROPHA OIL BLEND WITH DIESEL FUELLED ON VARIABLE COMPRESSION RATIO ENGINE”. Frontiers In Heat And Mass Transfer 5. doi:10.5098/hmt.5.10.