Entry tags:

mazda rx8, rotary 13b engine, rotary engine, volumetric efficiency

Volumetric Efficiency of a Rotary Motor Explained
rotary 13b engine

Compression 540º of crank rotation.

Combustion 810º of crank rotation.

Exhaust 1080º of crank rotation.

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In other words, it will take a rotary engine 1080º of crankshaft rotation to full an intake, compression, combustion & exhaust cycle. Or three crankshaft rotations for each cycle.

A piston completes a single stroke every single 180º of crank rotation:

• Consumption 180º of crank rotation.


• Compression 360º of crank rotation.


• Combustion 540º of crank rotation.


• Exhaust 720º of crank rotation.

A piston engine needs 720º of crankshaft rotation to complete a cycle. In other words, two total revolutions of the crankshaft.

A rotor rotates @ one/3 of the rate of the crankshaft. In other words, for each and every one revolution of a rotor, the crankshaft has done three revolutions. For instance when the tachometer on a car signifies 9000rpms, 1 rotor is turning at 3000rpms.

On two rotor engines, the front & rear rotors are offset 180º from every single other. A rotation of 360º of the crankshaft will provide the two rotors via the combustion stroke. Since each combustion chamber is -in the case of a 13B- 654cc, each and every 360º of crankshaft rotation will displace a total of 1308cc.

In buy to interpolate the cycles and volume displaced by a rotary motor vs. a 4 aide engine, we can use the following logic:

• A piston engine will take 720º of crank rotation to complete a cycle.


• In a rotary motor, 720º will create 4 combustion strokes:

1. 360º of crank rotation => 2 combustion strokes.


2. 720º = 360º x two


3. 720º of crank rotation => 4 combustion strokes.


4. 4 strokes = 654cc x 4


5. four strokes = 2616cc

For simplicity factors, we can stipulate that a 1.3L, two rotor rotary engine is equivalent to a 2.6L four aide, 4 stroke aide engine. It may possibly not be academically correct, but it is a comparatively easy way of visualizing how the rest of this write up and the formulas that are usually utilized to aide engines can be applied to a rotary motor.

Additionally, applying the very same calculations utilized to determine Volumetric Effectiveness (VE) on a aide motor, but for a rotary motor will yield optimistic results. If we were to take into account the rotary motor, a 4 stroke motor with a displacement of 1.3L, the benefits would render a VE of around one hundred% in a lot more than one particular instance, which is really unrealistic.

Did I make any feeling? Mmm perhaps not but, try to adhere to the up coming steps as I try to make perception out of what I have gathered so far.

A tiny experiment...

Properly, these days I eventually gave up and decided to do a little experiment that I located whilst looking for an useful technique to determine Volumetric Performance on a motor vehicle with out possessing to yank the engine from the car. I arrived across the following experiment: Calculating your cars volumetric effectiveness

I will assume that you are both as well lazy or exhausted to stick to the hyperlink, so I will make clear a bit on what does the experiment entail.