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Old 04-29-2016, 12:07 PM   #1
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Propane injection?

I've read all of the pros and cons in the cummins forums. Any thoughts on propane injection in a 5.9 12 Valve/ allison MT643 in a RE Thomas? I will certainly have enough propane on board.
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Old 05-30-2016, 10:53 AM   #2
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I have had interest in this as well. As you did, I have spent hours reading & studying the subject.

I am quite convinced that, properly done, propane injection can improve power, economy and reduce EGT's.

I have looked at it from an economy standpoint. Today I can buy diesel for $2.39-$2.59 in my area. Propane is generally $2.99-$3.29 a gallon.

What I have been completely unable to quantify is: How much diesel would I save after consuming one gallon of propane via injection?

I had considered the idea of an accurate fuel flow meter (2way) and a high refresh GPS to facilitate testing.

I would place fixed orifices in the intake and use a variable pressure regulator to vary the propane flow.

I could set up a particular driving situation and vary the propane flow while documenting driving condition, propane flow, fuel flow and speed.

I have some other ideas such as using an RV "safety valve" on the propane tank. It is a 12v solenoid valve that controls the propane flow at the tank. No power = no propane. I would control this valve with an oil pressure sensor. No oil pressure = no propane.

Several of the installs that I have seen are a simple "on/off" fixed flow setups. I really think that some kind of staged or variable approach would be more effective.

Without testing, I am clueless as to what to base the variable flow on. Throttle position? Boost? EGT? Some combination?

Any Arduino wizards out there to build us a controller???

Just some random thoughts from a guy with an overactive imagination...

Have Fun!!

S.
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Old 06-06-2016, 10:36 PM   #3
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Quote:
Originally Posted by PNW_Steve View Post
I have had interest in this as well. As you did, I have spent hours reading & studying the subject.

I am quite convinced that, properly done, propane injection can improve power, economy and reduce EGT's.

I have looked at it from an economy standpoint. Today I can buy diesel for $2.39-$2.59 in my area. Propane is generally $2.99-$3.29 a gallon.

What I have been completely unable to quantify is: How much diesel would I save after consuming one gallon of propane via injection?

I had considered the idea of an accurate fuel flow meter (2way) and a high refresh GPS to facilitate testing.

I would place fixed orifices in the intake and use a variable pressure regulator to vary the propane flow.

I could set up a particular driving situation and vary the propane flow while documenting driving condition, propane flow, fuel flow and speed.

I have some other ideas such as using an RV "safety valve" on the propane tank. It is a 12v solenoid valve that controls the propane flow at the tank. No power = no propane. I would control this valve with an oil pressure sensor. No oil pressure = no propane.

Several of the installs that I have seen are a simple "on/off" fixed flow setups. I really think that some kind of staged or variable approach would be more effective.

Without testing, I am clueless as to what to base the variable flow on. Throttle position? Boost? EGT? Some combination?

Any Arduino wizards out there to build us a controller???

Just some random thoughts from a guy with an overactive imagination...

Have Fun!!

S.
Bolt-on aftermarket to do this is sold out there, but it ain't cheap since it's pitched at the over-the-road guys. I want to know the same numbers that you do, but translated to dollars. Adjusted for whatever effect it has good or bad on engine life and preventive maintenance.
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Old 06-06-2016, 11:07 PM   #4
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get yourself over to a chassis dyno and pull some numbers torque rpm bsfh temp egt then with solid numbers the picture becomes clearer. charts graphs etc help sharpen the focus........
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Old 06-06-2016, 11:29 PM   #5
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It takes almost twice as much propane (gal per gal) to make the same amount of power. In other words, it takes two gallons of propane to make the same power as one gallon of diesel.

Its a straight thermodynamic calc. 1 gal of propane is 70,000'btu. 1'gal of diesel is about 135,000 btu.

As to the EGT reduction, this is controversial. Yes, initially, the EGT's drop, but there is quickly a point where the propane is crowding out air, and then the EGTS go to the moon. Diesels need excess air to function safely. Propane tends to crowd-out the air, meaning you can quickly approach the smoke/rich limit without realizing it if you're not watching the pyrometer.

Kohler did a ton of research on using propane and natural gas (methane) to offset the cost of diesel in their stationary power generators. Google "kohler bi-fuel". They found that, under very careful control, it works. But they made a lot of broken parts in the process. Basically they program their controller to provide very little gaseous fuel at low power, and only about 1/3rd gaseous fuel at high power. Only during part load operation was the gaseous fuel used in quantity, with better than 75 percent of part load operation energy coming from gaseous sources.

Note that these were stationary engines with a constant speed. Getting a variable speed engine to work like this will be a challenge indeed for the shade tree mechanic!

I think propane has its place, especially in electronically-controlled diesels (like a DT466e) where you cant monkey with the ECM to get more power. In these engines, 25 extra hp would be a godsend, and propane will give you that, as long as you stay away from the smoke/rich limt (which should be easily accomplished).
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Old 06-07-2016, 04:30 AM   #6
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I seem to recall reading about this in another forum, some fellow was using propane injection on a 7.3 (?) powered Ford truck. In his project, he had a simple on/off valve at the propane tank (regulated pressure, of course), which turned on at "full throttle", he had a switch under the pedal. Supposedly at full throttle, the propane boost came on gradually as the propane line was empty and had to fill from the tank to the engine, same was true for when he let up on the throttle. In his case, economy was not his main concern, it was power and acceleration.
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Old 06-07-2016, 07:47 AM   #7
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im a total Newbie at the thought but how does propane in the air stream not cause misfiring as you cannot adjust the timing of it... ie if your cylinder temp is high wouldnt the propane want to fire off way before the cylindr is at TDC?

-Christopher
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Old 06-07-2016, 10:50 AM   #8
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As best I understand it, we are not trying to "replace" diesel as the energy producing fuel with propane. We are adding propane to act as a catalyst of sorts to promote more complete combustion of the diesel fuel.

While I certain that the combustion of the propane is contributing to the total energy that is not the primary function of the propane injection on a diesel engine.
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Old 06-07-2016, 05:59 PM   #9
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Propane has a VERY high resistance to compression ignition, which is one reason that a propane-only spark-ignition engine can run higher considerably compression, advance and boost. The effective octane rating of propane is generally stated as between 105 and 110 (it changes with rich/lean mixture).

There is generally no problem of pre-ignition in a propane/diesel hybrid. The compression temperatures are not high enough to get it to go. But when the diesel injector starts to fire, the resulting flame front provides ample temp and pressure to light the propane, basically acting like a spark plug.

Its interesting to note that octane and cetane are sort of opposite of each other. Increasing octane signals a fuels increasing resistance to ignition by compression heat, while an increasing cetane number signals the fuels willingness to ignite quickly and smoothly upon injection.

With regards to propane being a catalyst of sorts, propane is a very simple molecule whose chemistry and behaviors are exceedingly well documented. Propane does not act as a catalyst in any way. It is a direct reactant, fully consumed in the combustion event, and contributes nothing but heat and pressure. In this manner it is the same as diesel fuel, gasoline, kerosene, natural gas, or any other fuel.

What propane can do, with careful management, is to change the placement of energy in the combustion event. In otherwords, you can change the instantaneous thrust on the piston at a specific point in the combustion event by changing the ratio of propane to diesel. You dont necessarily change the total area under the curve, just the placement of some of the energy (ie, robbing peter to pay paul). If you think about it, the mechanical advantage of the piston/crank relationship changes throughout the rotation sequence. Adding just a little umph in the right place can make a noticable change in hp, torque or throttle response.

I dont pretend to be a propane expert, but I've goofed with it for years in everything from lawnmower engines to big-block Fords. Its a neat fuel with some interesting properties, and like many, I want to play with it in a "big diesel", starting with the DT466e in my bus.
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Old 06-07-2016, 07:34 PM   #10
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interesting stuff.. I never realized that propane had that much resistance to combustion compared to diesel fuel.. but makes sense it could help even out the energy.. or im assuming a very temporary increase in cyclinder temperature to light the diesel fuel off quicker and more fully?

seems like the common denominator is making sure the engine has enough air to properly burn the fuel given... in a turbo diesel its kind of helped along since the more exhaust you have the more potential air you have.. (unless you hit the waste gate pressure... im assuming our bus diesel turbos have a waste gate to limit max boost.. and help keep cylinder temperatures down?)..

since the propane is injected in the air stream dont i run the risk of less air than required to burn the diesel and propane? as opposed to injecting itdirectly into the cylinder? (nearly impossible on a diesel)...

-Christopher
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