2.1.2. Low temperature differential engine configurations
A low temperature differential (LTD) Stirling engine can be run with small temperature
difference between the hot and cold ends of the displacer cylinder [5]. It is
different from other types of Stirling-cycle engines, which have a greater temperature
difference between the two ends, and therefore the power developed from the engine
can be greater.
LTD engines may be of two designs. The first uses single-crank operation where
only the power piston is connected to the flywheel, called the Ringbom engine. This
type of engine, that has been appearing more frequently, is based on the Ringbom
principle. A short, large-diameter displacer rod in a precise-machined fitted guide
has been used to replace the displacer connecting rod [5]. The other design is called
a kinematic engine, where both the displacer and the power piston are connected to
the flywheel. The kinematic engine with a normal 90° phase angle is a gammaconfiguration
engine [5].
Some characteristics of the LTD Stirling engine [5] are as follows.
1. Displacer to power piston swept volumes ratio is large;
2. diameter of displacer cylinder and displacer is large;
3. displacer is short;
4. effective heat transfer surfaces on both end plates of the displacer cylinder are
large;
5. displacer stroke is small;
6. dwell period at the end of the displacer stroke is rather longer than the normal
Stirling engine;
7. operating speed is low.