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Re: BMEP of Wankel Rotary Engine?  
Re: BMEP of Wankel Rotary Engine?  Carmon Colvin  Post Reply  Top of thread  Forum 
Posted by: Niko 04/10/2003, 13:49:43 Edit 
: 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 4stroke and 2stroke type of engine.: 2stroke BMEP = (HP * 6500) / (L * RPM): 4stroke 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 2stroke motor uses 100% of is displacement for combustion during one revolution where a 4stroke 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 : 2stroke BMEP = (HP * (6500 / 1.0)) / (L * RPM): 4stroke 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 ColvinFirst 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:4stroke BMEP = (HP * (6500 / .5)) / (L * RPM)2stroke BMEP = (HP * (6500 / 1.0)) / (L * RPM)Wankel Rotary BMEP (HP * (6500 / 3)) / (L * RPM)cause4stroke have 1 combustion every 2 revolution 720°2stroke have 1 combustion every 1 revolution 360°Wankel have 3 combustion every 1 revolution 360°alias4stroke have 0.5 combustion every 1 revol. 360°2stroke have 1 combustion every 1 revolution 360°Wankel have 3 combustion every 1 revolution 360°because 4strokes 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) / 9156BMEP = 363888 / 9156BMEP = 39.7i 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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