Compression Ratio

I've always had trouble understanding compression ratios. You gave the example in this video about how a 10.1 compression ratio allows for faster cooling in the exhaust chamber because there is more room as the 5.1 compression ratio doesn't have enough room to cool prior to exiting the chamber. Although excessive heat is harmful for a motor, doesn't it provide more power because there is more heat to spark and produce torque into the crank?

Could you please provide a link to the video in question, it's a little difficult to follow your query?

I suspect it's related to a property of an expanding gas where it cools with expansion. The more compressed it is initially, the greater the temperature drop that may be expected as it expands - like with a piston at TDC and moving down the bore.

Aloha Allen,

Concerning compression ratios in regard to the lesson on "Pressure Volume Cycle":

The instructor briefly explains that internal combustion engines with higher compression ratios have greater expansion ratios.

By allowing the combustion by-products (exhaust gases) to expand further more work is extracted over the expansion stroke improving engine efficiency.

Ultimately, it is the pressure acting on the piston's surface area that generates the torque at the crank. This force applied from TDC to BDC is the amount of work done by the system. Power is the rate (with respect to time) at which the work is being done.

As mentioned by the instructor, "All things being equal", we can reason that the 10:1 engine having a higher initial pressure will produce more force over a greater distance in the least amount of time.

Hope this helps,

Joe