[Thermodynamics] Quick question about ''Cut-off ratio'' in the Diesel Cycle.

1. Jun 19, 2010

Je m'appelle

[SOLVED] Quick question about ''Cut-off ratio'' in the Diesel Cycle.

So I've been studying the Diesel Cycle, and I've come up with something called the ''cut-off ratio'', which is simply a name for the ratio of expansion $$r_E$$.

But I'm getting different definitions for this ratio.

For example, in the below link the expansion ratio is given by $$r_E = \frac{V_1}{V_3}$$

http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/diesel.html#c2

And in this other link the expansion ratio is given differently by $$r_E = \frac{V_3}{V_2}$$

http://www.taftan.com/thermodynamics/DIESEL.HTM

I'm confused, can someone enlighten me please, are those expressions similar, if yes, how so?

Thanks.

Last edited: Jun 20, 2010
2. Jun 20, 2010

Je m'appelle

I've already found out what I was getting wrong.

Thanks for all the help I was provided.

3. Jun 29, 2010

The expansion ratio is basically the compression ratio, unless we're talking 'bout an engine with offset cylinder bank/crankshaft, which I've heard of very few, all of which being of small displacement because of balancing issues. The Toyo Aygo 1.0 petrol is one example. The Honda Inshight 1.0 is another.

With such engines, the compression and expansion ratios differ and the intake and compression, expansion and exhaust do not last for as many crank degrees.