13.5(√a – 28) = mean pressure
where a is the percentage of admission.
From this formula, table 11 is made.
331. Mr. Clark deduces as general results, from a very extensive and carefully conducted system of experiments, the following.
That the maximum useful admission is seventy-five per cent.
The minimum useful admission is ten per cent.
The greatest possible gain by working expansively is one hundred per cent., which is effected by an admission of ten per cent.
The best admission for engines having ports 1
14 of the area of the piston, and blast area from 1
13 to 1
16 of piston, at high speeds (from thirty to sixty miles per hour) and with considerable loads, is from sixty to sixty-six per cent. With a wider port and blast area, the best admission is seventy-five per cent.
The resistance due to the back pressure of the blast, varies as the speed squared, and inversely as the square of the area of blast orifice.
332. From the experiments made by Daniel Gooch, with the engine “Great Britain,” the following results appear.