Propane Injection + Water Injection Applications 2

[MCubed]

Please excuse my ignorance, but here it goes:

Currently I am modifying a NA EFI gasoline (non-diesel) engine to a turbo application. I have succeeded the first time, but now I am going into uncharted territory (larger turbo). I have been using an Aquamist Water injection system to help deter knock. Now I have seen the use of of Propane in some applications to be successful, but most of the applications have been diesel engines. So here is the questions I have for you automotive experts:

1. Can a combination of water and propane injection be used?

2. Where would be the best place to inject propane (from my experience would the in the intake runners for better dispersion into each cylinder)?

3. From my reading on other applications, once you use the propane injection you are able to run more boost (to a certain extent) on the same fuel system (i.e., same amount of fuel being used)? Propane's A/F is 15.7-15.8, so does that mean I would need to inject more gasoline to make up for the lean A/F of propane?

4. What are the pros and cons of running propane? What are the pros and cons of running water+propane (if it is possible)?

Any other information will be greatly appreciated.

Thanks,

Carlos

 

[Whittey]

AFAIK the propane injection for diesels is added before the valves and its combustion is to help mix the diesel and remaining air, so you can add more fuel making more power. I don't see gasoline engines improving in the same fashion because all you'll end up doing is displacing gasoline, which will put out more power anyway. As for anti-knock, I don't see a small amount of propane helping too much, and a larger amount will probably lose hp to a lower-boost all-gas setup.

I have no experience with this, so feel free to take it with a lb of salt


-=Whittey=-

 

[franzh]

Wow, I finally get to show up Whittey!

My specialty is working with gaseous fuels, propane and natural gas, and this question is not that uncommon.

Injecting small amounts of lpg vapor into the intake runners will have no effect on the relative octane of the total fuel mixture. LPG vapor does displace air, to the tune of about 8% at stoichiometry, and the use of a blower does help to restore some of the efficiency of the lost air.

The craze of "propane injection" for diesels is just that, a craze. Adding HC's to a fuel mixture that is already running very lean is providing BTU's, bringing the relative fuel mixture closer to stoichiometry, and the diesel engine is unthrottled, therefore, lots of power, but short engine life. Propane has an octane of 104, and has a higher ignition point than diesel, BUT the pressure rise time is MUCH faster than diesel, resulting in detonation / knock.

You are right that LPG has a stoich ratio of 15.5, but that is only .8 leaner than gasoline. My recommendation? Either use gasoline or propane, do not try mixing it. Unless you are prepared to design and install a dedicated LPG injection system that is speed density based, you are in for a lot of work for little or no benefit. There are some very good performing vehicles running LPG, and its very popular in Australia and New Zealand.

Franz

 

[MCubed]

Franz,

I knew you would chime in since you have participated in almost all the propane threads that I have read. Let me present this situation to you then:

Locally, there is a group of hot rodders tunning Toyota Twin Turbo Supras. The leader of the group is the one with the most experience with propane injection. He claims that he is running anywhere from 3-5psi more using the propane injection on the stock fuel system (this is probably to overcome the 8% substitution of propane for air). He claims his EGT's have also dropped dramatically. I assume this is because he is injecting a "large" amount of propane into his intake manifold causing him to run rich. His system works of a preset pressure switch that receives a pressure signal from the manifold and then activates the system once it reaches the threshhold This leads me to the following questions:

1. Is there a rule of thumb on what is a "safe" amount of propane to be injected using 93 octane fuel (I know safe depends on A/F and other variable)?

2. Is this guy on the short path to a catastrophic engine failure?

Again, any information regarding the questions in my first post or in this subsequent one would be of great help. And to clear this up, this is for a non-diesel engine.

Thanks,

Carlos

 

[MCubed]

PS. Bottom line, it sounds to me that he is using the propane as an "octane booster" as well as for cooling the intake charge leading him to the higher boost setting.

 

[GregLocock]

I think your diagnosis in para 2 was correct. His higher boost pressure merely compensates for the displaced oxygen, as a first approximation.

Let's see if maths will help:

Which is greater?

no propane:

100% air*(atmospheric+boost pressure)

8% propane, 4 psi more boost

92% air *(atmospheric+original boost pressure+4 psi)

If his non-propane boost pressure is less than 31 psi then the propane setup gives him more oxygen in the cylinder, and so the /potential/ for greater power.

Well I'm surprised. Cheers

Greg Locock

 

[Whittey]

Franz, i'm sure you can show me up many times over as i'm just a computer geek with an interest in cars (and if you're interested in something, why not learn as much as you can?)

As for propane being a craze, I dunno. My buddys uncle has a sweet F250 with a powerstroke pushing almost 700hp with a banks turbo kit, chip (I dunno what kind) and propane. Thats a big difference from stock, though he didn't dyno without the propane. The kit he had was supposedly good for 150hp? I dunno.

Just an idea i'm throwing out here, but would the propane itself act like a cushion to the ignition of the gasonline, in somewhat the same manner as water injection does?


-=I dunno=-

 

[MCubed]

Whittey,

I have seen a couple of turbo diesel trucks in my area using propane injection, but this is not uncommon with diesel engines looking for performance gains. I am interested in the application to petrol engines, and from what I can find, if forced induction is being used, there is no downside as long as you keep your A/F near stoichiometric.

GregLocock,

I follow you example somewhat, but get lost towards the end. Can you please give a more detailed explanation?

Thanks to all,

Carlos

 

[GregLocock]

Ultimately the power you can develop is limited by the quantity of air you can get intot he cylinder. What I did was to work out the potential amount of air in each of the two cases.

To my surprise in a very simple analysis (bear in mind that the higher boost pressure you use the higher the charge temperature, amongst other things), the extra boost pressure he can run more than compensates for the lost air occupied by the propane, up until 31 psi. Cheers

Greg Locock

 

[MCubed]

Greg,

Again, forgive my ignorance, but where do you come up with the 31psi boost pressure number and what happens once you go beyond 31psi and use propane?

Thanks,

Carlos

 

[franzh]

Yipes, take a day off and look what I've created!

I guess the reason your EGT dropped with propaned added was that it was burning and the gasoline was not, ie: running richer, condense fuel mixture, liquid effect cooling, but NOT from the richer propane, you would have gotten the same results from gasoline.

As for the diesel injection, I never said that it would NOT produce more power, it will, but that it MUST be used carefully.

We are and should be a law abiding community, and here in the US, Australia, most of Europe, and elsewhere in the world, emissions are a major part of a vehicles certification. Simply dumping fuel in an engine will not satisfy our EPA, and I cringe at the advertisements that state that it DECREASES emissions and LOWERS exhaust temps!

Sorry, I have spent many, many, hours on the dyno working on dual fuel engine systems. I had reams of paper with different fuel mixtures, substitution rates, and horsepower curves showing the results of propane or natural gas dual fuel fumigation. I have also ruined an engine budget with boo-boos, running too much fuel, or running manual systems where the driver had control over the amount of fuel being dumped into an engine.

Although I have the most respect for Greg's posts, I too am lost by his reference to 31 psi, but I am sure that there is relevence somewhere ;=)

Franz

 

[MCubed]

Franz,

So the bottom line of your explanation is that you can achieve the same effect with more fuel (petrol). But my question is the following:

Isn't the benefit of using propane injection is that it serves as a dual function: reducing air intake temp's and making the mixture richer thus allowing you to run more pressure on a forced induction vehicle?

As far as the use of this secondary fuel and EPA considerations, the whole purpose I would use it for is only track use, definitely not on a daily driver.

Thanks again,

Carlos

 

[franzh]

Unless you are injecting liquid propane into the intake, there is no intake cooling effect. Injecting liquid propane can be VERY trying as it is 270 times as dense as propane vapor! Just a tiny fraction can be more than an engine needs to operate. The control methodology for modern liquid propane injection vehicles is very critical, and I think far beyond the ability of a casual tuner (no offense intended).

You really do not need to run a richer mixture for a turbo, although adding propane vapor will provide more boost by continuing to burn when the exhaust valve opens (higher octane, longer burn duration). But this comes at the cost of power and exhaust system life, not the thing that is really necessary.

If you really want more pressure, work on the turbo scrolls and keep the fuel mixture at or near Stoich, and use an intercooler.

This is too much fun!

Franz

 

[PJGD]

The reason propane (or other gaseous fuel) is used in diesel engines, is that it enables a greater proportion of the air to be utilized. In a normal diesel engine, despite the best efforts of the design, development, and fuel system application engineers, it is virtually impossible for the injected fuel to find, mix with, and burn all the oxygen that was inducted into the cylinder. To much of the oxygen is in the headland crevice or in the dead area above the piston, so that a diesel very rarely achieves 100% air utilization (ie, 16:1 A/F ratio). In the past, it was typically around 80%, today it can approach 95% on the latest engines. So the theory goes; why not introduce 10 or 20% propane into the induction tract, and hope to make use of the otherwise lost oxygen because the propane will also be in those crevices. Whether it will be rich enough to burn is another issue. And as pointed out earlier, it can have a deleterious effect on cylinder pressures, pushing them over the structural limit in some cases.

PJGD

 

[buzz41]

Franzh -

I think you are estimating the criticalness of propane based on diesel use. There, a tiny bit too much liquid propane will, for sure, cause detonation, and very likely, a damaged engine. In this spark ign application, the addition of liquid propane will increase the octane by the high octane of the propane itself plus the octane enhancement of a richer mixture. The worst I can see for a too much propane condition is drowning the engine in too much fuel.

A question that comes to mind, though, is how best to use the latent heat of the liquid propane. Should it be introduced early in the intake stream, right at the valve or somewhere in between?

You really do not need to run a richer mixture for a turbo, although adding propane vapor will provide more boost by continuing to burn when the exhaust valve opens (higher octane, longer burn duration). But this comes at the cost of power and exhaust system life, not the thing that is really necessary.

Adding extra fuel for cooling is common to essentially all piston aircraft engines. For very high powered applications, the richness is increased well beyond best power to allow higher boost and higher net power. Increased richness tends to increase the effective octane considerably.

There is LITTLE OR NO correlation between octane rating and flame speed. Of course, if octane is not sufficient and DETONATION occurs, that is a quite different phenomena than normal flame front combustion and produces very destructive local forces - like TNT would.

Combustion cannot continue after all the oxygen is reacted, so continued burning through the exhaust event should not happen. I have often observed the common feather flame that is present on high powered piston aircraft during rich takeoff and climb. But, that is the external air reacting with the hot exhaust.

In the case of adding propane for enrichment, the exhaust system should not be damaged by a cooler exhaust unless the metal is sensitive to a carborizing flame and not an oxidizing one.

 

Why not inject methanol instead of water. It will give you a cooling effect, added power and contains its own oxygen It much easier to work with than propane. Heck just run the whole motor on it and crank up the boost, compression then you'll have good reliable hp as long as you don't lean it out.

 

[joereitman]

many people in the DSM world are beggining to experiment with propane, such as myself. maybe we can aid each other in our discussions...check out one of our threads and see what you think.

http://www.dsmtalk.com/forums/showt...02a1fad8dd50fe4f8&threadid=65627&pagenumber=1

it's lengthy but has tons of data and theory in it. my SN is eyebrowski over there.

 

[franzh]

Buzz41:
Sorry I missed your post.

I have spent several hundred hours on an engine dyno, and many thousands of miles doing some seat of the pants work tuning on the LP+Diesel fumigation system.

Admitting propane vapor into the intake manifold in small increments will provide power, frequently copious amounts, by adding additional fuel. Since the diesel engine in not throttled, there is almost always excess air, more than enough to combust propane even it is out of its AF range, since there is also diesel combustion taking place. Supplying excess propane vapor fuel to the point of flooding the engine is in my opinion, not possible. The engine will most likely destruct long before. Adding extra propane will NOT cool the combustion temps as there is no evaporative effect, and since it is a vapor, there is little heat absorption by the fuel.

The problem is that adding more than about 4% by volume propane vapor, significant pressure spikes occur, often prior to the diesel injection sequence. These sometimes inaudible pressure waves can cause significant damage, from burned and melted pistons, cracked cylinder heads, melted exhaust valves, burned turbochargers, cracked exhaust manifolds, broken studs, broken head bolts, blown head gaskets, and so on.

I have sitting on my desk a piston from a system that was installed and operating in the "Power" setting on a late model Cummins 24 valve. $15,000 later, the engine is still not reassembled. If I had the means of inserting a photo, I would.

My gripe is not with using propane as a fuel, many readers will no doubt notice my frequent posts here, but using it irresponsibly. The marketing guru's are making claims that are factually incorrect (whats new here!). Also, to even the playing field, the EPA has not approved the use of the propane dual fuel diesel engine. Many of the systems advertised on the web state claims that cannot be substantiated, offer user adjustable power levels, using components that are not DOT approved or installed in accordance to FMVSS or DOT or NFPA guidelines.

If some company wants to step up to the plate and offer a sealed tamper-proof system that has OEM support and backing, has full EPA testing with a valid certification, AND a warranty, you will find me in the front row, leading the cheers! Until then, I will be a critic.

Also, joereitman, the link you provided is not accessible.

Franz

 

[joereitman]

Franz- eyebrowski linked to this thread from a link I placed in dsmtalk.com, and accidentally replied in my name- I thought that couldn't happen? I will email the admin about that. My handle in dsmtalk is the same name as here. I do echo eyebrowsi's request for both groups of forum users to share information. By the way, the link provided above worked for me, but maybe not for you since you are not a dsmtalk member. You may need to just go to dsmtalk.com and find the propane thread under "parts reviews".

Also, your cautions and words to the wise stated above are well taken. Thanks

Joe

 

[joereitman]

Summary of logs injecting at 22psi, pre turbo, 2 turns open on tank and on needle valve:

No propane 3rd gear pull first- 4k to 6.5k. 10-13 counts knock for entire pull, 14-17 timing, .84 O2. This was about a 4.25 second pull. This was on ~25% toluene (nets about 97.5 octane with 93) at 20-21 psi, after a lot of boosting, so some heat soak going on.

Propane 3rd gear pull about 2 minutes later, no real cooldown, 4.3k to 6.35k, no knock, timing started at 19 quickly climbing to 22, .88 O2. This was a 3.5 second pull.

The use of toluene tends to minimize any octane affect of propane, due to small quantity of propane and fact that the small amount of propane at 104 to 110 probably is not impacting overall octane much. The temperature affect of vapor propane is not that great per prior measuring. So the turbulence/complete burn/elimination of hot spots/ buffering theories appear most responsible for the results.

The car was pulling so strong with the toluene mix that I could not tell much of a seat of the pants difference, but per the logger results it makes a difference, which I expect will be more obvious once I turn up the boost beyond where the 25% toluene would be effective.

Track testing will follow soon, maybe dyno too if I can find one nearby.

Joe