Description of volumetric efficiency of rotary engine

According to Auto-Ware.com, volumetric efficiency is:

… used to represent the amount of fuel / air in a cylinder in relation to the normal atmosphere. If the cylinder is filled with fuel / air at atmospheric pressure, the engine is said to have 100% volumetric efficiency. Superchargers and turbochargers, on the other hand, increase the pressure entering the cylinder, increasing the volumetric efficiency of the engine to more than 100%. However, if the cylinder is evacuated, the volumetric efficiency of the engine is less than 100%. Normally, the intake engine usually runs anywhere between 80% and 100% VE. Therefore, reading that a particular manifold and cam combination was tested to be 95% VE, we can see that the higher the number, the more power the engine can produce.

Characteristics of rotary engine compared to 4-stroke piston engine:

The rotor of a rotary engine completes one stroke for every 270 degree crank rotation.

• Incorporates 270º of crank rotation.
• 540º compression of crank rotation.
• Combustion of 810º of crank rotation.
• Exhaust 1080º of crank rotation.

In other words, the rotary engine must rotate the crankshaft 1080 ° to complete the intake, compression, combustion, and exhaust cycles. Or, crankshaft rotation 3 times per cycle.

The piston completes one stroke each time the crank rotates 180 degrees.

• Incorporates a crank rotation of 180º.
• 360º compression of crank rotation.
• Combustion of 540º of crank rotation.
• Exhaust 720º of crank rotation.

The piston engine requires 720º crankshaft rotation to complete the cycle. In other words, two complete rotations of the crankshaft.

The rotor rotates at 1/3 the speed of the crankshaft. In other words, for every revolution of the rotor, the crankshaft makes three revolutions. For example, if the vehicle’s tachometer shows 9000 rpm, one rotor is spinning at 3000 rpm.

In the two rotor engines, the front and rear rotors are offset 180 ° from each other. When you rotate the crankshaft 360 degrees, the two rotors go through the combustion stroke. Since each combustion chamber is 654cc for -13B, a total of 1308cc is exhausted each time the crankshaft rotates 360 degrees.

The following logic can be used to interpolate the cycles and volumes replaced by rotary and 4-piston engines.

• The piston engine requires a crank rotation of 720º to complete the cycle.
• In a rotary engine, 720º produces four combustion strokes.

1. 360º crank rotation => 2 combustion strokes.
2. 720º = 360ºx2
3. 720º crank rotation => 4 combustion strokes.
4. 4 stroke = 654cc x 4
5. 4 stroke = 2616cc

For simplicity, a 1.3L 2-rotor rotary engine can be defined as similar to a 2.6L 4-piston 4-stroke piston engine. It may not be academically correct, but this is a relatively easy way to visualize the rest of this description and how to apply the formulas normally applied to piston engines to rotary engines.

In addition, it applies the same calculations used to determine the volumetric efficiency (VE) of a piston engine, but with optimistic results for a rotary engine. Considering a rotary engine, which is a 4-stroke engine with a displacement of 1.3L, VE exceeds 100% in multiple instances, which is extremely unrealistic.

Did it make sense? Well, maybe not, but I’m trying to understand what I’ve collected so far, so be sure to follow the next steps.

A little experiment …

Well, today I finally gave up and decided to do a small experiment I found while looking for an effective way to calculate the volumetric efficiency of a car without having to pull the engine from the car. I came across the following experiment: Calculate the volumetric efficiency of a car

I think it’s a hassle or tired to follow the links, so I’ll explain a little about the content of the experiment.

Experience requires: (1) Vehicle with engine. (1) OBD-II scan tool; (1) Stock air intake with mass airflow sensor (MAF) on stock trim-According to the author, slight differences from factory stock, such as screen removal and sensor relocation. Gives little value to the experiment-(1) Private, safe, deserted road stretching.

Once you have all these items, the procedure is fairly straightforward. Install the scan tool on your vehicle to ensure that you can report engine RPM, intake temperature, and air flow. Vehicles from low engine speeds (2500rpm) @ WOT to the red line (or to the extent you want to move the sample) while recording intake temperature (IAT), engine speed (RPM) using a deserted driveway To run. ) & Intake Mass Airflow (IMAF).

Once you have logged the data, reread the experiment from the link provided and start calculating the numbers. The principle seems simple. Based on the calculated theoretical volumetric airflow of the engine (Renesis in this case) and the recorded data, the actual VE of a particular engine can be estimated. Provides the formula used at the end of this article.Let’s take a look at this chart for the time being [http://www.myrotarycar.com/mazdarx8/images/13B.MSP.Volumetric.Efficiency.020205.a.gif]..

The theoretical volumetric airflow was calculated assuming that the 13B MSP rotary engine has a displacement similar to a 2.6 liter 4-stroke piston engine at 720º of crankshaft rotation. Notice how the VE rises until the engine speed reaches 5500 rpm. It is safe to assume that the VE peaks at or near 5500 rpm as the engine is evaluated to produce peak torque. In addition, the volumetric efficiency plotted against engine speed can be safely assumed to mimic the shape and characteristics of the torque curve produced by the engine.

Note that the plotted VE is slightly linear. It starts at 80% and rises just above 100%. If the results of this experiment can be verified and the parameters used are accurate, the Renesis engine (at least in my car) is actually very efficient with respect to the naturally aspirated internal-combustion power plant-VE definition above. It means that.

Calculation of Volumetric Efficiency (VE) for Renesis (13B MSP) Rotary Engines:

Use the following values ​​obtained during the data log:

data:

Intake temperature (IAT) = 82ºF

Engine speed (RPM) = 8561 rpm

Airflow (MAF) = 27.3lb / min

Theoretical airflow calculation:

formula:

[(ED) x (rpm) x (VE)] / [(ES) x (C)] = TAF

variable:

ED = engine displacement [in³]

rpm = engine speed [RPMs]

VE = Volumetric efficiency [%]

ES = engine stroke coefficient [#]

Conversion coefficient from C = in³ to ft³

TAF = theoretical airflow [ft³]

Solution:

[(159.64in³) x (8561rpm) x (1)] / [(2) x (1728 in³/ft³)] = TAF

TAF = 395.42ft³

value:

ED = 2.6 liters (1308cc x 2) >> 159.64in³

You have arbitrarily selected rpm = 8561 rpm.

VE = This corresponds to the theoretical VE, so we assume VE = 100% (1)

To simplify the ES = 13B engine to a 4-stroke piston engine (ie 2.6L), we use a factor of 2.

C = 1728 in³ / ft³

Calculation of air density and temperature:

formula:

[(t1) / (t2)] = = [(d2) / (d1)]

variable:

t1 = temperature of air of known density [ºR]

t2 = Inspiratory temperature measured by the IAT sensor [ºR]

d1 = density of air at known temperatures [lb/ft³]

d2 = intake density [lb/ft³]

Solve [d2]:

[(t1) / (t2)] x (d1) = (d2)

[(491.67ºR) / (541.67ºR)] x (0.0808lb / ft³) = d2

d2 = 0.073341lb / ft³

value:

t1 = 32ºF >> 491.67ºR

t2 = 82ºF >> 541.67ºR

d1 = 0.0808lb / ft³

Volumetric flow calculation:

formula:

[(MF) / (d2)] = AVF

variable:

Mass flow rate obtained from MF = CAN Scan [lb/minute]

d2 = intake density [lb/ft³]

AVF = actual volumetric flow rate [ft³/minute]

Solution:

[(27.3lb/minute) / (0.073341lb/ft³)] = AVF

AVF = 372.233 ft³ / min

value:

MF = 27.3lb / min

d2 = 0.073341lb / ft³

Volumetric efficiency calculation:

formula:

[(AVF) / (TAF)] = VE

variable:

AVF = actual volumetric flow rate [ft³/minute]

TAF = theoretical air flow rate [ft³/minute]

VE = Volumetric efficiency [%]

Solution:

[(372.233ft³/minute) / (395.42ft³/minute)] = AVF

AVF = 0.94 >> 94%

value:

AVF = 372.233 ft³ / min

TAF = 395.42 ft³ / min

Is this remote and close to exact? I really don’t know! I simply took the time to do some research and gather information through various channels. If you have any comments, suggestions or corrections, please contact me!