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Re: BMEP of Wankel Rotary Engine?

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Posted by Niko (213.140.9.151) on April 10, 2003 at 13:49:43:

In Reply to: BMEP of Wankel Rotary Engine? posted by Carmon Colvin on November 18, 2002 at 17:12:57:

: First of all I am NOT an engineer so please forgive me if I use the wrong terminology or similar laymen mistake.

: I am trying to calculate the BMEP (Brake Mean Effective Pressure) of a Wankel rotary engine. Searching the net I have found one formula that is slightly different for a 4-stroke and 2-stroke type of engine.

: 2-stroke BMEP = (HP * 6500) / (L * RPM)
: 4-stroke BMEP = (HP * 13000) / (L * RPM)
: source: /engine_formula_automotive.htm

: The only difference between the two formulas are the numbers 6500 and 13000. The only correlation with a 2x difference between the two types of motors are the 2-stroke motor uses 100% of is displacement for combustion during one revolution where a 4-stroke motor uses 50% of its displacement for one revolution.

: The only way I can make this work between those formulas is to look at it this way.

:
: BMEP = (HP * (6500 / DU%) ) / (L * RPM)
: Using the Displacement % used as DU%

: OR

: 2-stroke BMEP = (HP * (6500 / 1.0)) / (L * RPM)
: 4-stroke BMEP = (HP * (6500 / .5)) / (L * RPM)

: A Wankel Rotary engine uses 33% of its displacement for combustion for one revolution output from the motor.

: Wankel Rotary BMEP (HP * (6500 / .333)) / (L * RPM)

: IS THIS A CORRECT ASSUMPTION?

: Data from an actual dyno run (measured at the wheels) of a slightly modified Mazda 13b (1308cc) non turbo motor put out 168 HP at 7000 RPM and 147 ft lbs of torque @ 4000 RPM.

: BMEP = (168 * (6500 / .333)) / (1.308 * 7000)
: BMEP = (168 * 19500) / 9156
: BMEP = 3276000 / 9156
: BMEP = 357.8
: This number seems really high compared to other BMEP readings I have seen for 4 and 2 stroke engines.
: And am I correct in assuming this is in pounds per liter?

: If this is completely wrong please help me with a formula that will accurately give me BMEP of a Rotary Engine.

: Thanks.

:
: Carmon Colvin

First of all please forgive me for my little English i'm an italian wankelieer web surfer so..

Following your reasoning i believe the formula is:

4-stroke BMEP = (HP * (6500 / .5)) / (L * RPM)
2-stroke BMEP = (HP * (6500 / 1.0)) / (L * RPM)
Wankel Rotary BMEP (HP * (6500 / 3)) / (L * RPM)

cause
4-stroke have 1 combustion every 2 revolution 720°
2-stroke have 1 combustion every 1 revolution 360°
Wankel have 3 combustion every 1 revolution 360°

alias
4-stroke have 0.5 combustion every 1 revol. 360°
2-stroke have 1 combustion every 1 revolution 360°
Wankel have 3 combustion every 1 revolution 360°

because 4-strokes have 1 combustion every 2 revolution wankel 6 combustion every 2 revolution and supposing same hp form 4t and Wk (at same conditions, rpm, ...), Wk will have 1/6 BPEM of 4t alias 4t=0.5 Wk=3, these two values in the formula works reducing BPEM as i wrote.

only an example for your car:
BMEP = (168 * (6500 / 3)) / (1.308 * 7000)
BMEP = (168 * 2166) / 9156
BMEP = 363888 / 9156
BMEP = 39.7

i do not add more, because i believe this task is too old, if not reply and i'll continue......
bye wankel friends.

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Subject: Re: Re: BMEP of Wankel Rotary Engine?

Comments:
: : First of all I am NOT an engineer so please forgive me if I use the wrong terminology or similar laymen mistake. : : I am trying to calculate the BMEP (Brake Mean Effective Pressure) of a Wankel rotary engine. Searching the net I have found one formula that is slightly different for a 4-stroke and 2-stroke type of engine. : : 2-stroke BMEP = (HP * 6500) / (L * RPM) : : 4-stroke BMEP = (HP * 13000) / (L * RPM) : : source: /engine_formula_automotive.htm : : The only difference between the two formulas are the numbers 6500 and 13000. The only correlation with a 2x difference between the two types of motors are the 2-stroke motor uses 100% of is displacement for combustion during one revolution where a 4-stroke motor uses 50% of its displacement for one revolution. : : The only way I can make this work between those formulas is to look at it this way. : : : : BMEP = (HP * (6500 / DU%) ) / (L * RPM) : : Using the Displacement % used as DU% : : OR : : 2-stroke BMEP = (HP * (6500 / 1.0)) / (L * RPM) : : 4-stroke BMEP = (HP * (6500 / .5)) / (L * RPM) : : A Wankel Rotary engine uses 33% of its displacement for combustion for one revolution output from the motor. : : Wankel Rotary BMEP (HP * (6500 / .333)) / (L * RPM) : : IS THIS A CORRECT ASSUMPTION? : : Data from an actual dyno run (measured at the wheels) of a slightly modified Mazda 13b (1308cc) non turbo motor put out 168 HP at 7000 RPM and 147 ft lbs of torque @ 4000 RPM. : : BMEP = (168 * (6500 / .333)) / (1.308 * 7000) : : BMEP = (168 * 19500) / 9156 : : BMEP = 3276000 / 9156 : : BMEP = 357.8 : : This number seems really high compared to other BMEP readings I have seen for 4 and 2 stroke engines. : : And am I correct in assuming this is in pounds per liter? : : If this is completely wrong please help me with a formula that will accurately give me BMEP of a Rotary Engine. : : Thanks. : : : : Carmon Colvin : : First of all please forgive me for my little English i'm an italian wankelieer web surfer so.. : Following your reasoning i believe the formula is: : 4-stroke BMEP = (HP * (6500 / .5)) / (L * RPM) : 2-stroke BMEP = (HP * (6500 / 1.0)) / (L * RPM) : Wankel Rotary BMEP (HP * (6500 / 3)) / (L * RPM) : cause : 4-stroke have 1 combustion every 2 revolution 720° : 2-stroke have 1 combustion every 1 revolution 360° : Wankel have 3 combustion every 1 revolution 360° : alias : 4-stroke have 0.5 combustion every 1 revol. 360° : 2-stroke have 1 combustion every 1 revolution 360° : Wankel have 3 combustion every 1 revolution 360° : because 4-strokes have 1 combustion every 2 revolution wankel 6 combustion every 2 revolution and supposing same hp form 4t and Wk (at same conditions, rpm, ...), Wk will have 1/6 BPEM of 4t alias 4t=0.5 Wk=3, these two values in the formula works reducing BPEM as i wrote. : only an example for your car: : BMEP = (168 * (6500 / 3)) / (1.308 * 7000) : BMEP = (168 * 2166) / 9156 : BMEP = 363888 / 9156 : BMEP = 39.7 : : i do not add more, because i believe this task is too old, if not reply and i'll continue...... : bye wankel friends.

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