jplecas

iTrader: (1)

I just saw photos of amemiyas new rx8 for d1. i was pretty surprised when i saw three separate fuel coolers in the trunk of the car! thought they were oil coolers but everything routes back to the swirl tank. could high fuel temps cause a loss of power?

jplecas

iTrader: (1)

i found someone had said they had a 10% loss on the dyno because of high fuel temperatures. i live in arizona so this could be an issue for me. my car is noticably slower on a hot day.

does temperature have a similar effect as different octanes? lower temps would take longer to reach the flash point because they have a farther gap to close. i dont want to worry about detonation because of the weather out here.. maybe a fuel cooler wouldnt hurt imo.

jplecas

iTrader: (1)

Maybe this would get more of a response in a different sub-forum?

peejay

I know my tune definitely changes with hot fuel vs. cold fuel. I can tune my idle and drivability to be perfect with a just-warmed-up engine, but if I drive it for a long enough time for the fuel in the tank to get heat soaked, the drivability starts to fall apart and the idle goes to crap.

The OEMs have made a mad dash to returnless systems for good reason: keep the fuel cool instead of constantly circulating it to the hot engine and back. They mainly did it for emissions reasons, since hot fuel results in higher evaporative emissions. But think about that a moment... hot fuel evaporates easier, or to put another way, the fuel takes less heat out of the intake in the process of evaporating. If you are running a carb or fuel injectors shooting down from the end of an intake trumpet, you're getting clear power benefits from this heat of evaporation cooling the air down and making it denser... and if the fuel is hot, you lose those benefits...

There's an amount of snake oil in cool cans, but there's some truth to their usefulness too.

jplecas

iTrader: (1)

I think i understand what your talking about. but i dont think its the process of evaporating that causes it. fuel has to sit in an open space for a long while to evaporate. but it wont stay there much longer though once its been ignited! your explanation makes me think about all those horrible emissions components and about trying to lower hydrocarbons. LOL but i know thats not where you were going with it. and i appreciate the reply, im thinking this thread should be moved to the rotary performance section.. maybe it would get more input. and i really want a straight answer on this.

If we were able to monitor the temperature of the air/fuel mixture before its been ignited, im sure we would be able to plot out the increase in power along with the decrease of fuel temps. but the closest we can come to that is monitoring IAT's. which is recorded before fuel is mixed. Someone correct me if im wrong, but i think since fuel is much denser than air, it would have the most effect on overall temps. Like Hot fuel would greatly increase the air temps. We spend so much time making sure our air charge is icy cool, but if were spraying heat soaked & uncooled fuel into it then temps still go up in the end. I guess thats why egt's are important during tuning?

It sounds like it would help to make sure the car isnt just at operating temperature before a tune, but also that fuel temps are somewhere near daily driving conditions. another reason why i prefer street tuning over dyno.

RotaryRocket88

iTrader: (7)

The latent heat of vaporization (heat energy required to undergo the phase change from liquid to gas) is the most important part of the process. A significant amount of heat energy is extracted from the intake air when this happens.

The addition of fuel to the intake air will always have a cooling effect, but the initial temperature will have a role in how much cooling goes on.

The heat energy required to increase the temperature of the gasoline to the boiling point is much lower than the amount required to perform the actual phase change (vaporization), but a change in fuel temperature would have a minor effect on the intake charge temperature.

The amount of heat required to raise the temperature of 1g of gasoline by 1š C is 2.22 Joules/g-C (heat capacity) http://www.engineeringtoolbox.com/sp...ids-d_151.html. But the latent heat of vaporization of gasoline is 348.9 J/g. http://www.afdc.energy.gov/afdc/pdfs/fueltable.pdf (150 btu/lb converted to J/g)

The boiling point of gasoline varies depending on ethanol content, etc..., so I'll just use 100šC for the example.

So for the energy required to raise 1g of 90šC gasoline to 100šC:

q = C_p * T = 2.22 J/g-C * 10šC = 22.2 J/g

Add the 348.9 J/g for vaporization, and you get 371.1 J/g of total energy used

If you had a lower starting temperature, say 70šC, and increased it to 100šC, you would have:

q = 2.22 J/g-C * 30šC = 66.6 J/g

66.6 J/g + 348.9 J/g for vaporization = 415.5 J/g total energy

So that 20šC starting temperature difference results in an energy change of about 12% (415.5 J / 371.1 J).

If we assume a stoichiometric air/fuel ratio (14.7:1), you have 1g of gasoline for every 14.7g of air. The energy needed to heat and vaporize the fuel is extracted from the air, and in this case it gets split 14.7 different ways. The heat capacity of air at atmospheric pressure & near the temperature range in question is 1.009 J/g-C (http://www.engineeringtoolbox.com/ai...ies-d_156.html).

So for example 1:

Delta_T (change in air temperature) = q / C_p / 14.7

Delta_T = (371.1 J/g) / (1.009 J/g-C) / 14.7 = 25šC

For example 2:

Delta_T = (415.5 J/g) / (1.009 J/g-C) / 14.7 = 28šC

So the temperature drop of the intake charge after gasoline is injected and vaporized changes by only 3šC. So for every 1šC the gasoline temperature increases, the intake charge temperature will increase by 0.15šC. That's not really much at all.

This is pretty simplified, but I think it still gives a good overview. Hopefully I didn't botch the math somewhere .

sharingan 19

iTrader: (16)

Excellent info! Sounds about right intuitively speaking. It would seem there isn't much to be gained from a performance perspective, but I suppose every little bit helps.

As far as oems, the money they would save on material by not having to run fuel lines back to the tank would probably be enough for them to justify return-less fuel systems, performance benifits aside lol.

peejay

Lines are cheap, reducing emissions is not. If they could reduce emissions by running ten lines back and forth, they'd do it.

Looking at the math, *wow* the heat of evaporation is a lot compared to simple cooling. I didn't realize it was that intense for gasoline.

Great, now I am thinking about fuel *heaters*. But only the fuel that stays near the engine. Hmm, another use for a returnless fuel system.

arghx

iTrader: (3)

The heat of vaporization is a much bigger deal on gasoline direct injection. You know Mazda's new Sky engines run 14:1 compression on 87 octane? That's because the fuel is injected directly into the intake during the compression stroke at about 100bar of fuel pressure, as opposed to around 3 bar on multiport injection. They also have a factory long runner 4-2-1 header.

arghx

iTrader: (3)

you guys should see this research paper Mazda did back in the 90s on prototype direct injected rotaries.

lastphaseofthis

iTrader: (8)

direction injection would make a world of diffrence on those of us wishing to run 87 octane in a high compression turbo engine. to bad there's so much $$$ involved in the parts themselves, i'm sure we could mill and drill some housings to accept them...

Slevin_FD

iTrader: (26)

I'm down. I really need to mail you a very large jump drive to fill up with awesome.

arghx

iTrader: (3)

Here are some diagrams from the old prototypes, which were pre-Renesis peripheral exhaust port engines with a strange "subchamber" ignition system.





Mazda has been playing around with injector locations in their prototypes for years and years now. A few years ago they patented a GDI rotary engine with three injectors. One was the "upstream" design. That's the primary injector. The second injector sprays inside the engine during the intake stroke. The third (auxiliary, tertiary, whatever you want to call it) is in the conventional intake port location. Staging is based on rpm and load. Here is a sketch of the two injectors located on the rotor housing:



The diagrams seem to show a lower cost solenoid-type injector that you would see in say a Ford GDI application. This is as opposed to the piezoelectric injectors used on common rail diesels and favored by BMW for GDI applications.

t-von

iTrader: (8)

^ You know I've been really curious as to what pressures Mazda is running on the new above injector placements? I wouldn't think you would need as much since it's NOT in FULL compression. All this time I was thinking that the injector pointing towards the intake was the primary. I guess I had that backwards. LOL!

arghx

iTrader: (3)

Of course these are still prototypes but I'm sure it's probably some slightly modified off-the-shelf injector system they got from a supplier (Denso most likely). So the fuel pressure probably varies between 20 and 100 bar like every other system.

If you look at the control strategies for GDI engines, fuel pressure usually has more to do with RPM and load than the injection timing. On piston engines they don't always fire during the compression stroke. Your basic "homogenous" style GDI engine, running lambda = 1 (not a lean burn/stratified engine) fires once during the compression stroke normally. However during warm up they will use various "split injection" strategies with two events per cycle in an effort to get the cat hot. Engines with more responsive injectors (piezoelectric instead of solenoid type) may have 3 injection events even during normal operation. That's how BMW does it on their homogenous engines.

JK64

I'm not sure exactly how this translates to street cars, but If you know anyone who races motocross seriously, they all chill their fuel. I was told that it is universally known as the easiest way to add (or save) hp.

j9fd3s

iTrader: (3)

the honda turbo F1 car actually had a fuel HEATER. of course the honda ran a really strange fuel.

i think this points out that what ever fuel you run might have a temp range that it works best at.

Liborek

Assuming complete evaporation. Unfortunatelly, many people and designs canīt utilize this fully... and choose to blame gasoline as bad fuel against miracle blends of today

peejay

The EcoBoosts are 10:1 with 12psi on top on 87 octane.

VW's direct injection engines are 13:1 N/A and 11:1 with 14psi on top, but they may require 91 minimum.

peejay

The Ford trainer told us that the Ford direct injection engines were piezo.

And that they went for the top tier of injector tolerances. No programming the PCM to a new injector's characteristics like GM.

RotaryRocket88

iTrader: (7)

The heat of vaporization of gasoline is pitiful when you compare it to water or methanol. Water is 2257 J/g and methanol is 1104 J/g. That's where the most substantial gains from aux. injection come from. Of course with water injection, an excess of water can interfere with the vaporization of the fuel being injected and lead to negative effects on power/efficiency. All the more reason to get the injection amount right.

The Ford Ecoboost paper you sent me mentions that some of the advantages to high pressure fuel injection are better atomization and easier evaporation. If more fuel can evaporate before ignition, the intake charge will definitely see a more significant temperature drop.

But it also discusses the problems direct injection has with cold start emissions due to the reduced amount of time between fuel injection, ignition/combustion & the exhaust stroke. Especially in turbo applications because of the heat loss from the turbocharger. One of the solutions mentioned is to retard ignition timing after a cold start to increase the amount of heat in the exhaust system.

The facts/rumors about the future 16X engine have me very interested in how efficient the rotary can become. Direct injection and laser ignition sound like huge advances for the rotary.

At least we don't have valves for the fuel to stick to. Though a portion will still stick to the intake walls, and another portion will exit through the exhaust ports unburnt. But for the purposes of this discussion, the fraction of fuel that never evaporates isn't important for comparison of fuel temperatures. We can still compare the effects on intake charge temp if we assume the same percentage of fuel

arghx

iTrader: (3)

The gasoline direct injection engines use a 6-hole solenoid type that appears to have a peak-and-hold style driver. The 6.4L diesels have piezo injectors. See attachments.

Retarding ignition timing during warmup is also used on regular old port injection (Rx-7's do it). What they were mostly talking about is retarding fuel injection timing. For cold start the Ecoboost uses the split-injection strategy that a lot of other homogenous GDI engines are using (see the Hyundai paper I sent you). So fuel is sprayed during the intake stroke. It flows into the special bowl in the piston and starts to form a stratified mixture near the plug. Then a second spray is fired very late in the compression stroke, right near TDC, to further concentrate the stratified mixture. An optimized split-injection strategy is used because it resulted in less fuel consumption and HC emissions without having to install tumble generation valves like Subaru and VW/Audi use.

Finally the plug fires and the very hot mixture goes right out the exhaust valve, past the turbo and into the cat. On a port injected engine you can't do this as well because you have to spray the injectors a lot earlier. But then again, on port injected engines that kind of strategy isn't usually needed in the first place.

peejay

One "dirty" little secret about DI engines is that the intake manifolds and ports, being completely dry of fuel, are bad to clog up with carbon. Even in an extremely close mounted port injection scheme where the injectors actually run into the cylinder head, there's enough runner wetting to keep things relatively clean.

Heck, I notice this on my port injected engines which all have had only two injectors. The primary runners stay clean, the secondaries get carbony, and when I was running the Turbo II manifold the secondary side plenum would get standing oil in it! And this was with engines that had no crankcase ventilation into the inlet tract.

The Subaru TGVs are used on port injected engines to speed up airflow past the injectors. I'm unfamiliar with the VWAG implementation...

arghx

iTrader: (3)

The lack of fuel spraying on the valves does present a challenge with carbon buildup but they're not all bad. The VWAG engines certainly have certainly developed a reputation for being the worst with carbon buildup though. The BMW engines haven't been out as long but they certainly don't have a reputation for widespread carbon buildup problems. But they also have pretty sophisticated air-oil separation for the PCV system. Injection timing, injector design and location, etc.

jplecas

iTrader: (1)

Thanks for all the great responses. Im understanding this better now. After reading about fuel vaporization I realized that liquid fuel doesnt burn. i guess i should have known that already but now i get why a big puddle of gas doesnt just explode.

here is a system that heats and vaporizes the fuel.

http://vfis.us/

The more surface area that is available to mix with air, the less unburnt fuel and energy loss we get. So if a higher fuel temp vaporizes more air, it results in a more efficient combustion. That article says HC's are ELIMINATED!?OMGWTF!? because they can vaporize the fuel 100% with the use of a heated vaporization chamber. once the gasoline is in a completely gaseous state, then its mixed with air and moved into the combustion chamber. All of the gas gets used, emissions are reduced, power is increased.. if thats all it takes why havent they been using it? I ended up reading that this is how a lot of those 200+ mpg claims were made in the 70s. and i found a huge list of patents of fuel vaporizers too.

http://www.rexresearch.com/ogle/1ogle.htm


I dont really want to make a new thread on fuel vaporization because it is effected by the temperature. I think its still relevant

http://freeenergynews.com/Directory/VapSter/

It looks like the way these guys are doing it is by placing the vap chamber directly above the exhaust manifold. Or using an electric heater. That article also mentioned using hot air from the radiator.