Single Rotor and/or Maximum BSFC
04-07-2007, 07:12 PM
#1
Junior Member
Thread Starter
Join Date: Apr 2007
Location: Sacramento, California
Posts: 7
I'm looking into using a 13B NA rotary motor for a hybrid project I'm working on.
I like the rotary motor for its small size and power/weight.
I'd like to get the maxium MPG out of the motor when its running my car at 50-70mpg which is where the motor will be run, otherwise it will not be running.
What RPM will get the maximum brake-specific fuel consumption?
Suggestions on what tuning can be done?
I really only need about 20-40hp from the motor, and was thinking just a single rotor would be enough power.
I've seen some prototypes for airplanes of single rotors, but it doesn't seem like a practical configuration, I don't want to spend all my time researching that problem.
Also has anyone used water injection to increase mpg?
thanks for any input.
Jack
I like the rotary motor for its small size and power/weight.
I'd like to get the maxium MPG out of the motor when its running my car at 50-70mpg which is where the motor will be run, otherwise it will not be running.
What RPM will get the maximum brake-specific fuel consumption?
Suggestions on what tuning can be done?
I really only need about 20-40hp from the motor, and was thinking just a single rotor would be enough power.
I've seen some prototypes for airplanes of single rotors, but it doesn't seem like a practical configuration, I don't want to spend all my time researching that problem.
Also has anyone used water injection to increase mpg?
thanks for any input.
Jack
04-08-2007, 01:08 AM
#2
Fabricator
Join Date: Jan 2004
Location: Central Ohio (Hebron) Zephyrhills Fla.
Posts: 1,322
Originally Posted by nimblemotors' post='867186' date='Apr 7 2007, 05:12 PM
I'm looking into using a 13B NA rotary motor for a hybrid project I'm working on.
I like the rotary motor for its small size and power/weight.
I'd like to get the maxium MPG out of the motor when its running my car at 50-70mpg which is where the motor will be run, otherwise it will not be running.
What RPM will get the maximum brake-specific fuel consumption?
Suggestions on what tuning can be done?
I really only need about 20-40hp from the motor, and was thinking just a single rotor would be enough power.
I've seen some prototypes for airplanes of single rotors, but it doesn't seem like a practical configuration, I don't want to spend all my time researching that problem.
Also has anyone used water injection to increase mpg?
thanks for any input.
Jack
The rotary will run well lean of peak EGT, and best efficiency will generally be at the best torque RPM.
Put a monster ignition system on a two rotor and lean it until it stumbles, then advance the timing and lean some more. You can get very close to piston BSFCs. Quicker on an engine dyno, with an adjustible controller. Use the RX-8 rotors or better yet the whole engine, (no overlap). Coast and slight throttle can be up to 35 degrees of advance. Ceramic covered rotor faces would help. Direct injection after the intake has closed would help a bunch. The closer to TDC the better. Heat the intake air as much as possible. Takes away top power but really helps the burn. Trigger the ignition several times around TDC.
That should get you close. The single rotor is a long project just by itself.
Lynn E Hanover
Picture is Richard Sohn's single rotor.
04-10-2007, 04:31 PM
#4
Member
Join Date: Oct 2004
Posts: 83
Rotomax is a company that makes a 85 Hp single and also two rotor Wankel rotaries based on Mazda dimensions that have air cooled rotors- this should help efficiency.
http://www.rotamax.net/products.html
Aixro is a 48 Hp single air cooled rotor wankel go-cart engines may be more suitable for your low power requirements. It has a secondary port that opens at 5,500rpm that bypasses the heated air. It is about the size of a Briggs and Straton complete and ready to run!
http://www.nova-racing.com/nova_gb/index.htm
http://www.cometkartsales.com/store/engine/aixro.htm
As already stated by Mr Hanover, the Mazda rotary can be tweaked to run lean as it was in the lean burn production versions before emissions required a catylitic converter and a 10 year warranty on all emmisions parts.
Mazda had more advanced experimental lean burn engines as well.
ROSCO was their ROtary Stratified COmbustion system. It used a reed valve in a small peripheral primary port an additional side air port for high load and semi-direct injection at the top of the rotor housing.
Under light load the peripheral port only fed air and the fuel was injected into the swirl created by its placement so the fuel was readily atomised. The reed valve stopped intake charge reversion from the peripheral primary port at lower rpms.
SCP was their Stationary Combustion Process engine. It had a small spherical chamber in the spark plug location that housed a fuel injector and spark plug.
All the fuel required for low load operation was supplied into this spherical stationary chamber and the rotors compression phase introduced air into the chamber.
This allowed a very lean total burn as there was a rich pocket in the spherical chamber that was easy to ignite and then the burning mixture expanded out into the normal rotary combustion chamber filled with just air for complete burn.
http://www.rotamax.net/products.html
Aixro is a 48 Hp single air cooled rotor wankel go-cart engines may be more suitable for your low power requirements. It has a secondary port that opens at 5,500rpm that bypasses the heated air. It is about the size of a Briggs and Straton complete and ready to run!
http://www.nova-racing.com/nova_gb/index.htm
http://www.cometkartsales.com/store/engine/aixro.htm
As already stated by Mr Hanover, the Mazda rotary can be tweaked to run lean as it was in the lean burn production versions before emissions required a catylitic converter and a 10 year warranty on all emmisions parts.
Mazda had more advanced experimental lean burn engines as well.
ROSCO was their ROtary Stratified COmbustion system. It used a reed valve in a small peripheral primary port an additional side air port for high load and semi-direct injection at the top of the rotor housing.
Under light load the peripheral port only fed air and the fuel was injected into the swirl created by its placement so the fuel was readily atomised. The reed valve stopped intake charge reversion from the peripheral primary port at lower rpms.
SCP was their Stationary Combustion Process engine. It had a small spherical chamber in the spark plug location that housed a fuel injector and spark plug.
All the fuel required for low load operation was supplied into this spherical stationary chamber and the rotors compression phase introduced air into the chamber.
This allowed a very lean total burn as there was a rich pocket in the spherical chamber that was easy to ignite and then the burning mixture expanded out into the normal rotary combustion chamber filled with just air for complete burn.
04-11-2007, 06:41 PM
#5
Junior Member
Join Date: Jan 2007
Posts: 2
If you're going to go through the EPA frowned on process of adding water injection, you might as well consider hydrogen injection through electrolysis of water. It can increase the flame front speed quite a bit, allowing you to run even leaner. Water or hydrogen injection likely won't pass current EPA car rules if you're interested in making a prototype that might reach mass production unless you can make the car work fine without it.
I'm pretty sure water injection will give you small boost in efficiency due to the extra heat energy vaporizing the water into steam, as well you can usually run more advanced timing due to the cooling effect. If you're going to go very very lean though, combustion temperatures actually drop pretty low and you risk quenching it. Water injection can be a big benefit to volumetric efficiency, though, which can help mpg depending on your efficiency points. I don't think it will be feasible at very lean A/F ratios.
The reason very lean conditions can cook engines even though combustion temperatures drop is that the flame front speed drops off as you lean it out, leading the flame front to 'dwell' on certain parts of the engine (more often than under say stoichiometric air/fuel ratios which actually is the point of hottest combustion) before petering out. This will cook your apex seals on a rotary and possibly eject too much heat to the oil. Ceramic coating the rotors will help with the latter, and ceramic apex seals with the former.
The faster flame front from hydrogen injection will help this too. Ceramic apex seals are $1000+($1800 for Ianetti) and I don't know how much ceramic coating a rotor costs - half this I suppose for a single rotor) and this possibly saves you going through the trouble of taking the engine apart to install them.
There is no way I can think of you can get a rotary to get 50-70mpg at cruise unless your car is very very light, and I don't see how that is possible with the weight of hybrid components. How do you plan to get around that or is it a secret? The Audi A2 can get that mpg now but its a 1.2L CDI turbo-diesel aluminum bodied car with a 1900lb curb weight.
A 2000lb car at 80mph is going to need like 24hp, maybe slighty less with a lot of work to reduce drag. You'll definitely want the smallest possible rotary motor to reduce throttle losses, but nobody sells them small enough that I'm aware of.
I'm pretty sure water injection will give you small boost in efficiency due to the extra heat energy vaporizing the water into steam, as well you can usually run more advanced timing due to the cooling effect. If you're going to go very very lean though, combustion temperatures actually drop pretty low and you risk quenching it. Water injection can be a big benefit to volumetric efficiency, though, which can help mpg depending on your efficiency points. I don't think it will be feasible at very lean A/F ratios.
The reason very lean conditions can cook engines even though combustion temperatures drop is that the flame front speed drops off as you lean it out, leading the flame front to 'dwell' on certain parts of the engine (more often than under say stoichiometric air/fuel ratios which actually is the point of hottest combustion) before petering out. This will cook your apex seals on a rotary and possibly eject too much heat to the oil. Ceramic coating the rotors will help with the latter, and ceramic apex seals with the former.
The faster flame front from hydrogen injection will help this too. Ceramic apex seals are $1000+($1800 for Ianetti) and I don't know how much ceramic coating a rotor costs - half this I suppose for a single rotor) and this possibly saves you going through the trouble of taking the engine apart to install them.
There is no way I can think of you can get a rotary to get 50-70mpg at cruise unless your car is very very light, and I don't see how that is possible with the weight of hybrid components. How do you plan to get around that or is it a secret? The Audi A2 can get that mpg now but its a 1.2L CDI turbo-diesel aluminum bodied car with a 1900lb curb weight.
A 2000lb car at 80mph is going to need like 24hp, maybe slighty less with a lot of work to reduce drag. You'll definitely want the smallest possible rotary motor to reduce throttle losses, but nobody sells them small enough that I'm aware of.
06-11-2007, 01:41 PM
#6
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Join Date: Mar 2002
Posts: 29
06-11-2007, 06:08 PM
#7
Senior Member
Join Date: Jun 2004
Posts: 524
Weight hurts acceleration, aero and friction hurt cruise.
You can get startlingly good fuel economy in a very heavy car as long as it has a low frontal area and is reasonably sleek, and you do little in the way of accelerating or decelerating. Think taxiing to the highway immediately after fillup and drive a constant speed until the tank is near empty.
You can get startlingly good fuel economy in a very heavy car as long as it has a low frontal area and is reasonably sleek, and you do little in the way of accelerating or decelerating. Think taxiing to the highway immediately after fillup and drive a constant speed until the tank is near empty.
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