Subject: Oil injection in the fuel
From: ACRE
Date: 1/8/2005, 11:03 AM



frank barbot wrote:







Hello,







I am working on engine conception (and a part of production) for



7



years, in



the past on gasoline and automotive and aeronautic applications.







I am now working for Mistral engines, with a base of Mazda



rotary



engine



13B



for aeronautic application.







So i would like to participate to your discution as a member.







I already do have a question.







The oil going to the head of rotor and apex seal coming from the



"secondary



volumetric" oil pump, through oil injectors, is mixed with air



coming



from



the inlet manifold. When is this flow usefull, what is his



fonction,



can



i



suppress this in certain condition ?







This question is very important for me, i am dimensionning a new



lubrification system dedicate to our application on that



function.







Best regards







Frank BARBOT







Welcome Frank. I'll repeat what I just said to Francois.







I don't have much on the pneumatic part other than what is in the



shop



manuals which is also not much. Mainly checking the one way



valves.







I think they function when the pressure is lower in the intake



chamber



than atmospheric. As far as I know no positive air pressure is



used



to assist the oil injection. Mazda main thrust on the design is



to reduce the quantity of apex seal oil as much as possible to



reduce emissions. A small positive displacement pump may be all



that you



need. Use a separate tank for the 2 cycle apex seal oil with a low



oil



warning light.







Here is one I made quite some time ago. I used off the shelf gear



pinion



stock for the rotors.







Paul Lamar







Frank,



I don't know if what I say will contribute anything BUT someone on



this



discussion group ( I can't remember who) said the 'oil metering



pump' was



a



two stage pump with a small amount of oil in Idle and fully on



(100:1)



just



above idle.







This may be different for the later Series 6 and RX8 models as they



are



electrically controlled metering and as Paul said the emphasis was



on



emissions control. Personally I would measure the out put at



different



RPM's, while running the engine on pre-mix.







Now having said all that, a recent trip to my local engine builder



mates,



informed me that they couldn't put an aftermarket engine management



system



on a Mazda, without first replacing the 'oil metering pump' with an



earlier



model manual pump- why! because there wasn't a Engine Management



System



manufactured to cater for 'oil metering'- why! because no other



engine



required this facility and it was a system for Mazda alone.







Is this the case with the Mistral Engine Management System?







George (down under)







Frank's job is to design the system for Mistral.







Paul Lamar







Mistral's DEM system can electronically manage electro-valves



precisely



metering the oil.  Frank wants to know if he can do away with the



pneumatic



system in this set-up.  I must admit we don't know as we have not



worked on



this system so far because it works fine... except that it's bloody



expensive to manufacture and to install (we are talking of copper or



steel



lines replacing Mazda's nylon line Paul "loves" so much for their



durability! :-)  ).







Cheers







Francois (across the pond)







I looked it up in the RX8 Service Highlights manual. Ironically I have



more info



on the RX8 than any other 13B. The function of the atmospheric air



supply



and the one way air valves in the injectors is to prevent the intake



chamber from sucking



oil out of the injection lines when the pressure in the intake chamber



is below atmospheric



which will happen big time if the throttle is closed while the engine is



still turning at significant RPMs. Definitely an emissions issue.



Probably



not a problem in an air craft engine. If the the oil is mixed with the



fuel



before injection that too would solve that problem. In other words no



direct injectors.







The PCM changes the electronic stepper motor metering pump according to



engine speed, engine



coolant temp and the amount of intake air. The fail safe mode is; the



injected



amount of oil is minimized and oil is injected only according to engine



RPM. The failure



of the stepper motor can be sensed by the PCM. The PCM then limits  the



amount of



fuel and hence the RPM and the power the engine can generate. Again a



fail safe



emissions issue since too much apex seal oil does nothing except



increase the



Hc emissions. In other words a limp to your car dealer mode :)







Aren't computers wonderful? :)







Paul Lamar




Ben Schneider wrote:






I don't know too much about them, but how does a 2-cycle oil injection



system work? (as on a snowmobile) Would something like that work, as you



would still have a seperate oil tank, but it mixes with the fuel before it



enters the engine. Perhaps more simple, and maybe less complicated? Just a



thought.







    Ben Schneider



I know very well were people are coming from with this practice of mixing 2-cycle oil in the fuel tanks or to inject it somewhere in the fuel lines.  It makes the complicated and expensive oil
metering system redundant and results in acceptable or even good lubrication of the apex seals and running surface with what is probably the best oil to avoid gum deposits in the seals' slits.



But let me set the record straight (at least from my point of view and I recognize there are others), this practice has big and unacceptable drawbacks for a commercial product IMHO:



1. Everyone is trying very hard to atomize and inject the fuel as well as possible to get the best possible combustion and efficiency.  That means keeping as much fuel away from the walls as
possible.  This objective is totally in opposition with depositing a layer of fuel-mixed oil on the trochoid surface.  In addition to 80-90% (hopefully) of the oil droplets that would stay in
suspension and be rejected either burned or unburned with the exhaust gases without having had any role in lubrication, you have 50% or more of the oil which get in contact with walls that are not
the walls you want it deposited onto, because they either don't need lubrication (rotor surfaces) or get it in another way (side-housing surfaces).  It means that from the quantity of oil you
introduce, something like 5% only does the job it was intended to do.  Talk about a waste and talk about unnecessary emissions!  How much is one supposed to mix?  2 to 4 ounces per gallon is the
recommendation if my memory serves me well?  That's 10 times more than what we use.  FYI, s piece of data from our Oshkosh trip:  Florida to Oshkosh and back + a few flights around OSH, 19 hours of
flight:  1 (one) quart of oil used, total.



2. Worse: the oil that goes through the engine without playing its role of lubricant is not some "innocuous" waste.  It sensibly increases the propensity to detonate and it clearly contributes to
higher EGTs.



3. Picture yourself as a salesperson trying to convince a non-rotorhead to purchase a rotary engine.  Now, you have to tell him or her that 2 different qualities of oil must be regularly added into



2 different tanks and, if one puts the wrong oil in the wrong tank, one may seriously damage the engine. Oh yeah!  One more thing:  one of these qualities of oil (the one you must add most often by
far) is generally not sold on airports.  ...If you can do it, then please let me know, I immediately offer you a job at Mistral Engines with a great compensation package!



I know that using engine oil in the metering system is not optimal, but the option is much worse IMHO, at least for a commercial product.



BTW, we have not observed, so far, any gumming of the seals whatsoever in hundreds of bench hours.  Maybe it's because we inject the right amount of oil?  We'll be especially careful to take this
aspect of things into account when we'll issue a final specification for the oil, but I already know that it will be an oil brand and/or quality that can be purchased in most FBOs.




Sorry for being vocal.



Francois Badoux


Not a problem being vocal. That's is why we are here. Lets put some numbers on it.
One fluid ounce per gallon is the norm. That is one part in 128 parts of fuel.

If you look at this chart from Mazda you need 80 or 100 cc per hour per rotor
or say 200 cc per hour to keep the seals cool. Since there are about 33 cc per 
fluid ounce that is 6.6 fluid ounces per hour. At 13 gallons per hour that is 
about half an ounce of 2 cycle oil per gallon. Since the Mazda rotary  racing world 
has tens of thousands of hours on one ounce mixed per gallon 50% getting to the 
apex seal is not that bad. Also I might add the only way the side seals get 
oil is from the apex seal oil. In theory, if the oil scrappers are doing their 
job on the sides of the rotors they get no oil from the crankcase.

In the early days Mazda introduced the oil into the carb float bowl. It was only
later they added direct injection and after the emission regs became draconian.

This weird rotor housing wear obviously was the result of a failed apex 
seal oil injector. Mazda also spent a lot of R&D time on how the injected apex seal 
oil was distributed across the rotor housing surface which I can document.
Not a fait accompli by any means.

Racing Beat with their 1200 HP 3 rotor turbo charged rotary found that up to four 
ounces per gallon did not cause detonation. (One part in 32)

I am not saying you have to mix it manually with the fuel. I am saying you will
get better results if you inject it into the fuel and not into the rotor housing
directly. I know you don't like the idea of forcing the pilot to mix it
with the fuel.
 
Check my arithmetic.

Paul Lamar
 
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