alt="images"/> is
(1.33)
For
(1.34)
so
(1.35)
As
(1.36)
The cylinder volumes predicted by Equations (1.33) and (1.36) are compared in Figure 1.11 for a value of Volume.m listed in the Appendix. Both equations give identical results at bottom dead center and top dead center. The approximate volume relation underpredicts the exact cylinder volume by about 18% at
Figure 1.11 Cylinder volume vs. crank angle for
The instantaneous piston velocity
(1.37)
Equation (1.37) can be nondimensionalized by the mean piston speed
(1.38)
Using the Matlab® program Velocity.m listed in the Appendix, the nondimensional velocity
Figure 1.12 Nondimensional velocity vs. crank angle for
If we neglect terms of
(1.39)
The acceleration
(1.40)
Note that the velocity and acceleration terms have two components, one varying with the same frequency
The reciprocating motion of the connecting rod and piston creates accelerations and thus inertial forces and moments that need to be considered in the choice of an engine configuration. In multicylinder engines, the cylinder arrangement and firing order are chosen to minimize the primary and secondary forces and moments. Complete cancellation is possible for the following four‐stroke engines: in‐line 6‐ and 8‐cylinder engines; horizontally opposed 8‐ and 12‐cylinder engines, and 12‐ and 16‐cylinder V engines (Taylor 1985).
Scaling of Engine Performance
The performance characteristics of three different diesel engines are compared in Table 1.1. The engines are a four‐cylinder 1.9 L automobile engine, a six‐cylinder 5.9 L truck engine, and a six‐cylinder 7.2 L military engine. Comparison of the data in the table indicates that the performance characteristics of piston engines are remarkably similar when scaled to be
