The analysis done here further shows that the point of maximum indicated work is quite far from the maximum shaft work point and is in fact on the unfavorable side of the brake output curve. In the case shown in Figure 10.4, the maximum indicated work occurs at about ? = 1 .7 and ? = 90 . At this point, shaft work is a low and mechanical efficiency is a dismal ? _m = 0 .35.

As another example of this, extreme but real, consider the design of an engine intended to operate at a low temperature differential with ? =0 .9, and, for simplicity, assume ? = 0. Numerical optimization shows that the maximum specific indicated work is , and this is attained when ? = 1 .6 and ? = 89 . At this point, . Even if the mechanism effectiveness is a fairly good E = 0 .8, Formula (3.2) shows that shaft work for this engine will be negative:

In other words, this engine could not even run itself. Even if the mechanism effectiveness were raised to 0.9, the engine still could not run itself. From the optimization table 10.1, maximum specific shaft work for a Schmidt gamma engine with ? = 0 .9, ? = 0, and E = 0 .8 occurs at a quite different geometry, namely, ? ^* = 0 .29.