shaunv74

There has been a great deal of positive results for piston engines using direct fuel injection techniques gaining more horsepower and more gas mileage. These are things most people are complaining about with the renesis.

Could this engine benefit from this technology? From what I've read it doesn't look like the renesis is direct injection. Am I wrong?

Could you route the fuel injectors next to the intake ports directly on the side housings? Mazda is currently using the technology in the Mazdaspeed 6 with favorable results so they know about it.

I'd like to hear some thoughts and comments from the rotary experienced out there...

rotarygod

Mazda has played with this concept several times over the last 30 years. The first of these attempts was in the ROSCO concept.

This stood for ROtary Stratified COmbustion system. This engine used a fuel injector that fired directly into the rotor housing. It was mounted nearly on the top of the engine facing down. It actually slightly faced the downward side towards the intake ports. This engine had both peripheral and side intake ports.

Next came the SCP (Stationary Combustion Process). This had only side intake ports. There was a "pre-chamber" where the leading plug is on our engines. Inside this chamber fired the fuel injector and the spark plug and then the mixture was sent out into the enigne.

Later on came the DISC (Direct Injection Stratified Charge) and DISC II concepts.

Nothing has ever come to production through Mazda from all of these experiments.

Other manufacturers however have brought direct injection rotary engines into use. Racing Beat's 3 rotor 3 turbo Bonneville RX-7 used direct fuel injection. They placed 2 injectors immediately next to the peripheral intake ports. It obviously worked as this is the worlds fastest rotary powered car. When I find the picture of the fuel injector layout, I post it here.

The PATS company out of Maryland makes 1 rotor APU's (auxillary power units) for small business jets. These are peripheral ported 1 rotors that make about 18 horsepower. They are direct injected with JP4 av gas. I do have a picture of this but it is too large to post here.

fullsmoke

Shrink the picture in M$ Paint!
I've also wondered the same thing...

FS

TRZ750

I don't really have any direct knowledge on direct injection (DI) on the rotary, but do have a number of comments. First is I wonder why DI isn't used more as most all manufactures have done extensive testing. Probably either the cost of manufacturing is too great compared to the benifits. Or there are some technical or runability problems, like at idle or low speed. As a example is that the boat outboard manufactures, Mercury, Johnson-Evenrude, and Yamaha have all used DI, but have all had problems. Especially with long periods of idle and plug fouling. If Mazda has found some advantages of DI with the rotary they could easily be waiting to use DI as a advancement in the future after the RX8 is established. Remember their 13B was first out in 1974 (RX4), but not used in the RX7 (released in 79 with 12A(B)) until 1984.

Many people using this site forget about business reasons like above. Mazda and other manufactures are very concerned about manufacturing costs, legal issues like liability, future sales directions (along with market studies), patient issues (can't use other manufactures ideas), and testing and development costs. One example is that many here may want more power, but they could only represent 10% of the targeted market, so Mazda decided to hold off. What % of RX8 owners ever become members? I for one am happy with the current power of my RX8.

neit_jnf

The Renesis has a similar layout for the primary injectors, they inject fuel directly into the combustion chamber through the primary intake ports and the fuel gets further atomized/mixed by the air injectors. I think the secondaries and tertiaries are regular type mounted in the manifold.

I wouldn't call this exactly direct injection, as it is still injected during the intake cycle. Direct injection as applied to diesel or gdi engines allow for various modes of operation where the gas gets injected during the intake cycle, compression cycle, or at TDC depending on several variables like engine load, rpm, throttle position, etc.

It is popular in Europe and other non-US countries. The main reason for it not being applied more widely in the US is the high sulfur contents of the gas, special catalitic converters have to be used.

The benefits of direct injection are many; engines can run in ultra-lean conditions (40~50:1 AFR) at cruising speeds, can use higher compression (there are DI engines that use 12~14:1 CR on pump gas) and boost pressures (as seen on the MS6 9.5:1 CR and 15.6 psi). And advances are being made towards compression ignition gasoline direct injected engines. A higher compression engine is more efficient.

Good info here: http://www.mitsubishi-motors.co.jp/i...GDI/page5.html

Check out the pictures and animations

rotarygod

The Renesis isn't really any different than the 13B's in terms of where fuel is injected. All of these enigne s place the primaries in the intermediate housing but they are still firing into the intake runners before it enters the engine. Racing Beat actually physically installed the injectors into the rotor housings firing at the rotors themselves.

shaunv74

If Racing Beat has a working setup...has Mazda offered to license the technology? If the idea has promise and they've been working in a similar direction, I'm supprised the two have not collaborated on it. Especially since Racing Beat has worked so closely with Mazda for so long on rotaries.

Is there something about the rotary cycle that makes it more difficult than a piston engine to get the technology to work?

brillo

I'm pretty sure the reason its not standard yet is cost. Mazda didn't give the renesis guys a huge budget, so they decided to work on the biggest issue, which was emissions, hence the new side exhaust system.

More and more new engines are coming out with this. It will be like fuel injection was in the late 1970's, lux/ high performance will get it first, then it will trickle down. You can thank the diesel guys for the DI technology, since its been Europe's love fest with diesel that has made this practical and now more cost effective. for the rotary, the biggest issue is the more holes you drill into the rotor housings, the more potential for pressure leaks as the apex seals passes over them. Now if the injectors were all placed right next to the intake openings into the chamber, that wouldn't be an issue.

I would kill to see a DI 6 spark plug all aluminum 2 rotor. hopefully thats what's in the new RX7

neit_jnf

The combustion chamber rotates, also the shape of the chamber is not ideal; all this adds complexity to the system

Rhumb

It is actually the odd, elongated shape of the rotary combustion chamber that I would think would make DFI uniquely beneficial to the rotary. I think a lot of the thermal efficiency have to do with diffuculties in maintain efficient flame fronts across these wide, oddly shaped chambers with a lot of surface area to further quench the flame. DFI might better allow very precise control over where the fuel/air mixture is actually located in the combustion chambers, basically limiting it to a much more centralized, contiguous area that can be more efficiently burned. But that's the theory, of course the reality and cost of reaching that reality are other things.

neit_jnf

I've been thinking about this application... you would need several injectors positioned around the rotor housings to allow for different injection times but it could be done and I think would be very beneficial

brillo

I think with 2 injectors in the intermediate housings and an injector in each rotor housing, you could prolly skip having an additional two since you could have such precise control over the fuel flow.

The biggest issue with DI for non diesel engines has been getting the injector nozzles to survive the heat from the chamber, that and computers with the sufficient processing power to meter the fuel properly. Now that’s not an issue.

I liked RG’s idea too of having a 1.3L 3 rotor, smaller chamber would be more efficient in terms of flame travel.

robrecht

Now that Mazda has placed a 13B-DI (direct injection) rotary in it's Senku hybrid concept, maybe this thread can be revived.

Does anyone know or care to speculate how much increased power or fuel economy is likely from direct injection.

Is it likely that direct injection could make it into the 2007 model year?

Please note, I'm not asking about the whole hybrid thing, just the direct injection modification to the renesis.

Thanks!

TeamRX8

iTrader: (25)

just a matter of time, these guys will eventually have one too, they've already done some diesel rotary versions

http://www.freedom-motors.com/

RichardK

My parents owned a Carisma GDi from 1998 for a couple of years - it was a stupidly cheap contract hire care so the dull styling was forgiven.

Driven hard, it gave 35mpg, but would maintain 90 through a set of bends that my 924S had struggled to hold 80 through - with five people in the Carisma. Generally it gave 44mpg, which for a car that size and weight wasn't bad, but was no better than my 1990 catless Golf GTI 8v - and with similar performance, albeit with less safety equipment, emissions kit and so forth in the Golf. (The Golf weighed about 850kg or so IIRC, the Mitsubishi around 1200 at a guess - I could look it up).

If we want the safety kit, we need the GDI, but more efficient car designs would be better IMO. I wonder what the Golf would have given with that GDI engine in it...

Both the Golf and Mitsubishi, when driven on fumes in a "Oh god I need to get to the fuel station and it's empty" moment for the Mitsubishi and "Let's see how high I can get the MPG on this" on the Golf, returned 52mpg.

Those are Imperial Gallons, so the numbers would be smaller for US gallons of course.

rx8wannahave

Interesting...what ever they do, you can't go wrong adding power and fuel economy to the RX8....the question is how much is Mazda willing to invest into the rotary engine.

I'm giving them the benefit of the doubt (business reasons, Ford's say in all of this, etc) but if they just let the RX8 die off like the RX7 (while I understand it was too pricey) I just might not get another rotary.

I love the car and engine, but if Mazda shows me they are doing all of this with the half-*** approach, I won't get another one...just keep my 8 and go chase my V8 lust in the new Camaro.

Meanwhile...I'll continue to faithfully wait on Mazda and see what happens. Frankly, either they are committed to advance the rotary or they aint.

With all due respect of course since they are the only car company making rotary powered cars...I understand, but I want to see more development on the engine I've grown to love and I worry if Mazda has it in them.

robrecht

Any one care to speculate how much increased power or fuel economy is likely from a direct injection Renesis???

rotarygod

That is a question that is hard to answer without actually knowing how they did the fuel injector placement in the engine. Just because it is direct injection does not neccessarily mean more efficiency. It would be a waste of time to do it without getting an increase so it's pretty safe to assume an efficiency gain of some sort. Exactly where the fuel is injected and when will have a big effect on the power and efficiency.

Right now with the way fuel is injected into the engine, it is not terribly efficent at combustion. When the rotor moves through the compression phase. The a/f mixture gets pushed into the dish in the rotor face. What most don't realize is that as the chamber gets smaller the a/f mixture actually moves backwards through this area towards the trailing plug until it encounters the trailing apex seal. This means the mixture is richer at the trailing plug than at the leading plug. When the leading plug fires, it is igniting a leaner mixture than is present at the trailing plug. It is the a/f ratio at the point of combustion that counts. At idle the Renesis fires the trailing plug first which means it is firing a richer mixture. As a result of this you can run a leaner overall a/f ratio at idle. Remember it's the a/f mixture at the point of combustion that counts and not the total as measured at the exhaust sensor. As a result of this technique the Renesis uses 70% less fuel than the last 13B at idle. The leading plug fires first everywhere else. Fortunately as long at there is not positive pressure in the intake (boost) you can always run trailing first to increase efficiency. That's something that can be done now. I've actually negative split (trailings firing first) on my RX-7 with a degree of success. It works!

Now the reason I got into that is to show the importance of where the a/f mixture is concentrated. Mazda has tried a special direct injection arrangement in the past that had 2 fuel injectors in the side housings firing into the combustion chamber directly besides the leading spark plugs. This would form the rich mixture centered in front of the leading plug itself rather than spread out everywhere else. The easiest way to try to simulate the same thing is with negative split. There's a whole lot to be had with some creative tuning.

rx8wannahave

^so tell us again why you aint working for Mazda? Dang it RG...we need people like you in there, I know I'm inpatient but give us something Mazda...other than new options and fluff...

I would love to see a NA rotary come out from Mazda making 300 flywheel (or 265whp) all the while getting maybe 19/25 in mpg. (20/26 would nock my socks off for a rotary)

There, I gave numbers that have no factual information or evidence to support it but to give the newbs out there (like me) something to dream about...lol.

robrecht

Thanks, rotarygod.

I realized my question was speculative but didn't imagine I would get such an erudite dodge! Bottom line, I'm trying to decide if I want to wait for potential 2007 improvements and miss out on a year of RX-8 driving (don't worry, I still love my Miata). But aside from that question, I'm also just trying to learn a little bit about rotaries so thank you very much for your response!
Thanks, robrecht!

auzoom

I often wondered if it was possible to run a wankel rotary on diesel and with the fuel "crisis" I wondered if Mazda would look at a diesel instead of hydrogen. Guess its to far from the norm.

Freedoms ability to run in both a spark based mode and compression based mode with the flick of a switch is very interesting (I think I read this right http://www.freedom-motors.com/diesel.html). Imagine being able to flick to Diesel to get some nice low down torque and then back to petrol fuel for some big HP!

Or am i way off the mark?

Andrew