Joined Jun 2007
4K Posts | 1K+
south east WA Australia
Hossack engine (square pistons)
from the same hossack front end designer
The Hossack Engine ? a Square Piston Two Stroke
Objective
There are several gains to be had from this format.
Prime among these is the ability to make the port timing asymmetric. Conventionally piston ported 2-stroke engines open the exhaust port first followed by the transfer ports. This is an acceptable sequence but as the cycle continues the transfer ports close before the exhaust and because of this up to 30 percent, by some studies of the fresh unburned charge is lost down the exhaust port. The HOSSACK design seeks to avoid this loss by varying this sequence. This is achieved by positioning the ports on different sides of the lobe. In this way the transfer ports can open later and close later and the exhaust can open sooner and close sooner. By this it is claimed the losses normally associated with 2-strokes can be limited.
Secondly the HOSSACK engine having dispensed with the wrist pin and its associated structures can be built much lighter. The normal wrist pin requires a strong support structure at the proximal end of the connecting rod as well as a beefy structure in the piston. Add to this the retaining circlips and a bearing and the weight of the rod itself. The HOSSACK engine provides a lighter structure allowing for higher engine RPM or lighter construction.
Thirdly in a conventional engine all these just mentioned masses stop and start 2 times every cycle. At TDC and at BDC these masses decelerate to and accelerate from a complete stop. The HOSSACK design changes this by virtue of its shape. The lobe never stops. It rocks. There is no instant in which the lobe is stationary.
It takes up to 30 degrees of crank rotation for the total mass of the lobe to change direction over TDC and up to 40 degrees of crank rotation over BDC. By this change in the reciprocating pattern the end loads generated are reduced which could lead again to a lighter component or higher RPM.
Mini V8
[YOUTUBE]i3VVI6Auvys[/YOUTUBE]
from the same hossack front end designer
The Hossack Engine ? a Square Piston Two Stroke
Objective
There are several gains to be had from this format.
Prime among these is the ability to make the port timing asymmetric. Conventionally piston ported 2-stroke engines open the exhaust port first followed by the transfer ports. This is an acceptable sequence but as the cycle continues the transfer ports close before the exhaust and because of this up to 30 percent, by some studies of the fresh unburned charge is lost down the exhaust port. The HOSSACK design seeks to avoid this loss by varying this sequence. This is achieved by positioning the ports on different sides of the lobe. In this way the transfer ports can open later and close later and the exhaust can open sooner and close sooner. By this it is claimed the losses normally associated with 2-strokes can be limited.
Secondly the HOSSACK engine having dispensed with the wrist pin and its associated structures can be built much lighter. The normal wrist pin requires a strong support structure at the proximal end of the connecting rod as well as a beefy structure in the piston. Add to this the retaining circlips and a bearing and the weight of the rod itself. The HOSSACK engine provides a lighter structure allowing for higher engine RPM or lighter construction.
Thirdly in a conventional engine all these just mentioned masses stop and start 2 times every cycle. At TDC and at BDC these masses decelerate to and accelerate from a complete stop. The HOSSACK design changes this by virtue of its shape. The lobe never stops. It rocks. There is no instant in which the lobe is stationary.
It takes up to 30 degrees of crank rotation for the total mass of the lobe to change direction over TDC and up to 40 degrees of crank rotation over BDC. By this change in the reciprocating pattern the end loads generated are reduced which could lead again to a lighter component or higher RPM.
Mini V8
[YOUTUBE]i3VVI6Auvys[/YOUTUBE]
