It is good to have a basically efficient engine,
but to get the most of it, it must be used
in an efficient manner and with proper engine accessories.

Intake Cut Off Valve - Efficiency Versus Power

Note: The following is not necessary for the engine to run great!

Quasiturbine Efficiency

The Quasiturbine is quite efficient as is by many standards. But for those who want still more efficiency, the intake cutoff is the ultimo possibility for the pressure fluid modes. Like the pistons and the turbines, the Quasiturbine needs a minimum pressure and flow to sustain the free spinning at the working rpm, and there is not benefit to cut off in order to produce an exhaust pressure output lower, which would not even provide the no load free rpm.

Power Level versus Efficiency

First, great care must always be taken not to confuse engine efficiency with the system efficiency. A 100% engine efficiency could still led to a low system efficiency, as efficiency of each system component multiply themselves... Efficiency is not a constant engine parameter, but it depends very much of the engine operation conditions and regime, and of the intake cut off decision in compressed fluid mode. Very often, it is not possible or even suitable, to keep an engine running at its optimum efficiency regime.

When an engine is used with compressed fluid in pneumatic, steam, expander or turbo-pump, there is always an inerrant competition between the Power level and the Efficiency. Longer the gas pressure is provided to the chamber cycle, more power it will produce, but less expansion this gas will have within the machine, and consequently less gas relaxation will occur before the exhaust time - An efficiency penalty imposed when high power level demand. Optimum would be a perfect reversibility situation, where the chamber is initially and rapidly pressurized (ideally with hot gas) to such a level that expansion ends near the atmospheric pressure and temperature at exhaust time. In such a system, increase in Power can be obtain either by increasing the intake pressure, or by increasing the open duration of the intake valve.

The practice of truncating the intake cycle is common to all positive displacement engines. Old steam locomotive did have some cut off capability once cruise speed attained, as have many of the today vane type engines. Of course, his valve must be synchronized somehow with the engine shaft or the chamber cycles, and the in-line gas pressure regulating reservoir must be located before the cutting valves.

One should also remember that heat is produced when compressing a gas, and as much as possible, this heat should not be discarded by cooling the compressor, but rather stored with the compressed air in an insulated pressure tank (if the compressed gas is going to be relaxed within hours of its compression). This heat would then be efficiently used in the adiabatic cooling relaxation process and insure a much better reversibility of the compression-expansion cycle.

Total Energy

For applications using a fix amount of air (like high pressure cylinder), intake cut off power reduction can generally be compensated by using higher intake pressure, and by doing so, the overall energy available from a cylinder could increase substantially.

Power Premium Value

Not only energy has a price, but power also! Because utilities will pay a prime value for peak power, storage facility may allow to substantially increase the overall economic of a system (some storage projects do not bother with energy generation, but just buy low cost off peak energy to resell it at a premium during peak periods). Nothing is free, but it could make (economical) sense not to run the system always at optimum efficiency. This is why the engine ability of efficient power modulation is a very valuable one.

Windmill Energy Storage Case:
For example, a windmill could produce a steady power over the day, but thanks to storage, much higher power could be deliver for a short period of time during the peak demand period. This extra power involves equipments and storage facility which demand an extra premium. It could also affect the total efficiency of the system, because it could require not to cut-off as much during such peak, with the advantage to keep supplying the customers. Windmill energy storage is not needed only for low wind period, but to harvest the most energy even when the demand is lower than the power generated, and also to provide supplemental peak power (in excess of the windmill capability) when needed. Because it does not make much sense to store an energy which is needed right away, a simple windmill system could include in addition to the generator, a reversible Quasiturbine compressor - air motor to store exceeding energy only, and to help speedup somewhat the windmill when needed, or to run its generator alone while the windmill is un-clutched (By the way, if you local energy network accepts to store your windmill energy for free, you are lucky, but this will not last for ever...).

Sophisticated Cut Off Valve

Sophisticated optimization can be achieved through the use of controlled valves at intake ports. Modern electro-mechanical valves can be computer controlled for optimum opening duration in accordance with the power level and other running parameters. The main advantage of electronic control is that it allows infinite possibility of dynamic timing and opening duration. The best would be 2 valves, one for each intake port, but linking the 2 ports together would require only one valve.

At this time, such an accessory system is not currently available for the prototypes, and buyers are free to make their own if needed.

Simple Mechanical Cut Off Valve

Simple intake cut off valve can be made by using two perpendicular radial holes in the central shaft as part of the rotary valve. A brass or nylon disk with similar perpendicular radial holes being fitted over the shaft, with the 2 exits going respectively to their respective Quasiturbine entry port. Diameter of the holes in relation to the shaft diameter determine the fraction of the time the flow is on. Typically a fraction around 50 to 65 % is a fair test debut. Synchronization timing is done by moving slowly the disk angle position before bolting it in place.

Example of a simple rotary synchronization intake cut off valve,
using 3/16 of an inch perpendicular cross holes on a 3/4 inch diam. shaft.
Valve open 65 to 75% of the time.

Alternatively, a cam on the central shaft could drive mechanical valves located at both intake ports, with the further advantage of reducing the residual volume between the valve and the chamber (which reduces the geometric compression ratio). Mechanical valve driving train do not offers much flexibility, but it is very worthwhile considering its relative simplicity.

A variation of this simple mechanical cut off valve could be efficiently located at each intake port, providing a proper driver gear and strap to rotate them in phase, or better, to be driven by 2 digital electrical motor controlled by computer, and synchronized from the signal of a microphone listening at the exhaust noise...

Cut off valve located at each intake port.
On the left, the shopper shaft has been removed and is shown for detail.

This simple accessory system is not currently offered with the prototypes, but could eventually be on special request.

Exhaust Pressure Pulse

An other simple mechanical way would be to make use the exhaust pressure pulse to mechanically activate the opening of an intake valve.

Other Advantages

Efficiency is the main reason for the use of the intake cut off valve. But because the intake cycle is truncated, exhaust noise is substantially reduced.

More Technical

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Quasiturbine Rotary Expander