Page 203 - Handbook of Energy Engineering Calculations

An engine located below sea level can theoretically develop more power
than at sea level because the intake air is denser. However, the greater
potential output is generally ignored in engine-selection calculations.

ENERGY ANALYSIS OF I-C ENGINES

An indicator card taken on an internal-combustion engine cylinder has an
2
2
area of 5.3 in (34.2 cm ) and a length of 4.95 in (12.7 cm). What is the
indicated mean effective pressure in this cylinder? What is the indicated
horsepower of this four-cycle engine if it has eight 6-in (15.6-cm) diameter
cylinders, an 18-in (45.7-cm) stroke, and operates at 300 r/min? The indicator

spring scale is 100 lb/in (1.77 kg/mm).

Calculation Procedure:

1. Compute the indicated mean effective pressure
2
For any indicator card, imep = (card area, in ) (indicator spring scale,
lb)/(length of indicator card, in) where imep = indicated mean effective
2
pressure, lb/in . Thus, for this engine, imep = (5.3)(100)/4.95 = 107 lb/in 2
(737.7 kPa).

2. Compute the indicated horsepower

For any reciprocating internal-combustion engine, ihp = (imep) LAn/33,000,
where ihp = indicated horsepower per cylinder; L = piston stroke length, ft; A
2
= piston area, in ; n = number of cycles/min. Thus, for this four-cycle engine