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  • Writer's pictureRipl


Test results and a conversation with Paul Baxter, inventor of the Ripl Rotary internal combustion engine.

The results are in from the thermodynamic study of the Ripl Rotary Internal Combustion Engine (ICE) and they are good. They are alarmingly good. We have shown them to other internal combustion experts and have been met by disbelief. But that’s okay as here at Ripl, where our goals are to invent and develop paradigm-shifting technology at pace, we are used to being met by disbelief.

Read the results below. They are followed by a chat with Paul Baxter, the inventor of the Ripl Rotary engine. He will explain the core concepts that deliver such revelationary revolutionary performance and help you become a believer.

N.B. The results are derived by comparison of digital models simulating the performance of the Ripl Rotary internal combustion engine and a conventional piston internal combustion engine. Further detail about the research scope can be found at the bottom of this document. All assumptions about the Ripl Rotary engine are comparable and conservative.

Key Results:

• The key novel elements in the Ripl Rotary engine design are that the;

o Induction, compression, and expansion process are not the same volume, and

these volume ratios can be defined and optimised

o Combustion process happens at a constant volume where the duration can be

defined and optimised

• The following engine performance data was calculated;

o RIPL rotary engine efficiency (v1.2) 51.0%

o Conventional piston engine efficiency 36.4%

o Relative improvement 40.1%

• Due to the there being increased power strokes per revolution and an increase in efficiency

of the RIPL engine, there is a four-fold increase in the power to weight ratio over the

contemporary technology (Ford Ecoboost V6 3.5L engine).

Hello Paul. Please could you introduce yourself and explain a little about the Ripl Rotary engine?

Hello everyone. I am the inventor of the Ripl Rotary engine and I don't blame you if you are having some doubts about the figures you have seen. We can't show you the mechanism, as it’s secret, but I can let you in on how the Ripl Rotary extracts so much more motive power from the same amount of fuel and hits those high power to weight ratios.

Cool. So where is the extra power coming from?

This is pretty simple. The Ripl Rotary engine follows the Atkinson rather than the Otto cycle. To put it simply the Otto cycle is a standard piston that crushes a set volume of fuel and air, ignites it and then expands to the original volume and exhausts the hot expanding gas. The Atkinson does the same but expands to a greater volume than the original fuel air volume extracting more motive power from the fuel. The Ripl Rotary engine has full control over the intake volume, the compression ratio, and the final expansion volume meaning you can get every last bit of grunt into the drive rather than throwing it away out of the exhaust.

Is that it?

Well no, there are other key aspects to the design. When you light the fuel air mix in a piston engine it takes a while to burn and whilst this happens the pressure in the cylinder climbs. Sadly the piston is in constant motion so the maximum force downward can only be generated if you light the fuel slightly before full compression.

This leads to a counter productive pressure increase when the piston is still on its way up but it pays off overall. In a perfect world you would squash the fuel air mix to its chosen volume and then ignite it and hold it still whilst it burns. Once it is full combusted you then start your power stroke. The Ripl Rotary engine does this trick perfectly but without interrupting its rotation in any way.

That’s very useful, thank you…..

Hang on, there’s more! It only has four moving parts and they are all bearing mounted. It does work on both sides of its piston heads at all times so there is very little wasted volume. It produces a circular motion by default meaning no crank shafts or sumps with the associated friction and power to weight losses. It also makes pops rather than a stream of fast moving exhaust air meaning you can dampen the noise through an exhaust. It’s a game-changing design and we look forward to showing it to some like-minded people.

Our gratitude to our friends Marine-I and Riventa for supporting this stage of the engine development. We are presently in conversation with several potential partners about the next stage.

If you would like to be involved or learn more, please contact Andy Crouch at

The specified project scope for this study was as follows.

• Simplified Thermodynamic analysis of engine to include:

o Pressure-Volume & Temperature-Entropy graphs for a complete cycle

o Pressure, Temperature and Volume relationships to Stroke/rotation position

o Comparison to an equivalent piston engine

o Comparison to ideal Otto and Atkinson Cycles

o The relationship between Fuel Fraction Burned and Combustion Time

o The relationship between Ignition Advance and Net Work

▪ Identify optimal ignition angle for given inputs

▪ Predicted Power Output

• Approximation of thermal losses through cycle and an estimation of mechanical

efficiency from the literature.

• Produce a theoretical model.

• Produce an output report from the model detailing all the above, highlighting the

efficiencies of the different steps in the process.



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