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Old 13-01-2015, 05:43   #1
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LPG mixed with diesel engine

I have gone through half the threads but can't find if anyone has tried LPG mixed with their diesel like some vehicles do. It must go in with the air intake like in some petrol/LPG engines.
It's supposed to give an extra 20% power I read somewhere or maybe brings it up to turbo performance and cleans up the combustion some.
Thought it might be handy to fit a big LPG tank on board, fill up at bowser LPG prices (when you can find them and it is about 1/4 cost of bottle gas in Australia) to run the cooking stove and just stop using gas for the engine when the LPG tank gets low, so you can still do the cooking.
But is it an economic excercise with the 20% and claimed engine life improvement.
Phalo
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Old 13-01-2015, 06:05   #2
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Re: LPG mixed with diesel engine

Propane injection, along with Nitrous Oxide injection is used for hot rodding Diesels, I would stay far away from that on a boat, way far away. When hot rodding a Diesel you keep adding fuel and turning up the boost until you get to the smoke point, which of course if un-burned fuel, Nitrous Oxide or propane can help burn this fuel, all this assuming of course the motors internals are strong enough to survive it and since your only doing it for a few seconds, usually you don't melt your pistons, but thermal damage is cumulative, so you will end up melting your pistons if you don't blow the bottom end or heads off first of course.
There is at least one other member here that used to Hot Rod his Diesel truck.
Mines for sale, it's a four door Dually that will pull 18,000 lbs down the highway in over drive, and turn a 13 sec quarter mile when you drop the RV, and it's not a strong enough tune to use propane or Nitrous.
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Old 13-01-2015, 06:12   #3
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Re: LPG mixed with diesel engine

Horsepower is like a teeter-totter with longevity on one side, power on the other. Every time you change the value of one side, the other will move too.

You never mentioned the hull type, but assuming a cruising yacht.... Hull speed is your enemy, not horsepower!
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Old 13-01-2015, 07:08   #4
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Re: LPG mixed with diesel engine

Interesting thread. I've not heard of injecting LPG into diesels, but some googling shows a number of Aussie websites, and that it's not unheard of in Europe. I can see the potential application - not least being able to fit a smaller diesel and still get the power needed; perhaps this would work well in a diesel-electric application.
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Old 13-01-2015, 07:51   #5
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Re: LPG mixed with diesel engine

Lpg acts like nos in a gas engine. Blow up the motor and engine pieces might make a nice hole in the boat. Dont do it

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Old 13-01-2015, 09:53   #6
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Re: LPG mixed with diesel engine

The system to which you are referring is called bi-fuel or dual fuel, and it is sometimes found in the diesel generator business. It involves the introduction of natural gas into the intake tract of the diesel engine although LPG can also be used. The purpose of bi-fuel can be two fold: to lower the cost of operation and to extend the run time of an engine where fuel take size is a concern. Lowering the cost of operation depends on the relative cost of BTUs between diesel fuel and the selected gas. Extending the run time can be important in the case of standby gen sets fitted with relatively small tanks. Connecting to natural gas can help reduce the frequency of diesel tank refills.

Contrary to what is implied in this thread, the use of bi-fuel does not increase the power output of the engine, the engine merely makes the same power on a different blend of fuel. Here's why......Lets say you have a diesel generator running at 1800 RPM and developing 200kW of power. Now you start to feed CNG into the intake manifold. The CNG is ignited by the burning diesel fuel in the combustion chamber and starts to produce additional power. This extra power would start to drive the engine RPM up, but as soon as it does, the governor reacts to the RPM change and cuts back on the amount of diesel fuel injected, lowering the RPM back to the original 1800. Same amount of power output, different fuel.

The same thing would happen on your boat. You are tooling along at 2200 RPM and you begin to inject LP or CNG into the engine. Because you have the throttle set for 2200 RPM, the governor will attempt to maintain 2200 RPM and it will reduce the amount of diesel injected in proportion to the amount of LP or CNG injected. No gain in power, just a change in fuel.

There could be a set of circumstances where this could be a problem however....Lets say you have a 3000 RPM engine, and the boat is overloaded to the point where you can only achieve 2700 RPM at WOT. So you are thrashing along at full throttle only making 2700 RPM, the governor is injecting 3000 RPM worth of fuel, the temp gauge is climbing a bit and you start to inject some CNG. Now the governor wont pull back on the diesel fuel rack because your throttle setting calls for 3000 and you arent there yet. So what happens is that the CNG takes your engine from being merely overloaded to being really overloaded! The engine RPM could climb up to and over 3000 RPM which would cause the governor to reduce fuel some, (while still being overloaded) or the engine could overheat if it doesnt have enough reserve designed into the cooling system. Or things might start to come apart.

Given the complexity in the gas control valving, the potential for explosive gas leaks, and the somewhat remote possibility for engine overload, I suspect bi-fuel wont be the next hot fad in the sail boat world.

DougR
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Old 13-01-2015, 10:31   #7
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Re: LPG mixed with diesel engine

KaBoooom!
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Old 13-01-2015, 10:38   #8
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Re: LPG mixed with diesel engine

go to the most recent issue of pacific mariner magazine as the first large LPG operated ships are now under construction.
the lpg goes(injected) in under high pressure and after the diesel starts the combustion process
still pretty experiemental.
is the extra weigh worth the amount of fule needed to push the boat through the water?


i doubt it


having two sources of explosives aboard the boat, to me is not wise
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Old 13-01-2015, 10:52   #9
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Re: LPG mixed with diesel engine

LPG conversions have been done for decades, and conversion kits are widely available. Google will show them. My company converted some forklifts to LPG so that they could be used inside a warehouse. It is not a difficult project to accomplish. LPG is not a practical propulsion fuel for boats.
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Old 13-01-2015, 11:09   #10
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Re: LPG mixed with diesel engine

Insane idea for a boat. Dragster, container ship, stationary gen. set a good idea. Just the weight of the LPG tank of any size would be prohibitive on a boat. I'm sure you only intended this as a brain teaser.
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Old 13-01-2015, 11:52   #11
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Re: LPG mixed with diesel engine

Yes, LPG conversions have been around for many years, and there are lots of forklifts and on-highway engines running LPG and CNG. But the common denominator in most all of these engines is that they started life as an engine with a spark ignition system.

Remember that diesel engines have no spark ignition system, the diesel fuel being ignited by the heat of compression only. Diesel fuel auto ignites at about 400 deg.F and LPG and CNG auto ignite at about 1000 deg.F. This difference in temperature makes it impossible to convert a diesel engine to run exclusively on LP or CNG without designing and installing a spark ignition system to get the gas burning. This makes currently available diesel/ LP conversion kits really bi-fuel kits, and not so practical for small diesel applications.

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Old 13-01-2015, 12:08   #12
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Re: LPG mixed with diesel engine

Quote:
Originally Posted by DougR View Post
The system to which you are referring is called bi-fuel or dual fuel, and it is sometimes found in the diesel generator business. It involves the introduction of natural gas into the intake tract of the diesel engine although LPG can also be used. The purpose of bi-fuel can be two fold: to lower the cost of operation and to extend the run time of an engine where fuel take size is a concern. Lowering the cost of operation depends on the relative cost of BTUs between diesel fuel and the selected gas. Extending the run time can be important in the case of standby gen sets fitted with relatively small tanks. Connecting to natural gas can help reduce the frequency of diesel tank refills.

Contrary to what is implied in this thread, the use of bi-fuel does not increase the power output of the engine, the engine merely makes the same power on a different blend of fuel. Here's why......Lets say you have a diesel generator running at 1800 RPM and developing 200kW of power. Now you start to feed CNG into the intake manifold. The CNG is ignited by the burning diesel fuel in the combustion chamber and starts to produce additional power. This extra power would start to drive the engine RPM up, but as soon as it does, the governor reacts to the RPM change and cuts back on the amount of diesel fuel injected, lowering the RPM back to the original 1800. Same amount of power output, different fuel.

The same thing would happen on your boat. You are tooling along at 2200 RPM and you begin to inject LP or CNG into the engine. Because you have the throttle set for 2200 RPM, the governor will attempt to maintain 2200 RPM and it will reduce the amount of diesel injected in proportion to the amount of LP or CNG injected. No gain in power, just a change in fuel.

There could be a set of circumstances where this could be a problem however....Lets say you have a 3000 RPM engine, and the boat is overloaded to the point where you can only achieve 2700 RPM at WOT. So you are thrashing along at full throttle only making 2700 RPM, the governor is injecting 3000 RPM worth of fuel, the temp gauge is climbing a bit and you start to inject some CNG. Now the governor wont pull back on the diesel fuel rack because your throttle setting calls for 3000 and you arent there yet. So what happens is that the CNG takes your engine from being merely overloaded to being really overloaded! The engine RPM could climb up to and over 3000 RPM which would cause the governor to reduce fuel some, (while still being overloaded) or the engine could overheat if it doesnt have enough reserve designed into the cooling system. Or things might start to come apart.

Given the complexity in the gas control valving, the potential for explosive gas leaks, and the somewhat remote possibility for engine overload, I suspect bi-fuel wont be the next hot fad in the sail boat world.

DougR

This may be how it works on a regulated engine such as a generator, but in a throttle controlled engine like a boat or truck it does increase power. I have a series of dyno sheets from my 2002 Duramax tested at PPE (Pacific Performance Egineering) with and without the Powershot 2000 system energized.

The PS2000 system was advertised to add up to 100hp and 175 ft-lbs of torque. On my engine, it added 98hp and 250 ft-lb of torque. The major advantage was it spooled the turbo up much sooner in the rpm range, which helped lower EGTs and really reduced smoke output. Based on the way turbos work and the fact that the PS2000 system both increases max boost up to the wastegate setting and increases boost earlier in the rpm range, less load on the engine would probably result in less boost, less propane and lower power gains.

The PS2000 system consists of a main solenoid at the tank and an adjustable, boost indexed pressure regulator which starts at about 8 psi of boost and feeds in propane in a linear rate as boost rises.

The major drawbacks of the system (and all propane injection power adders) is that you need a turbo engine for boost to control the propane, and the propane is an untimed fuel source, which can be dangerous (like nitrous) if it's not carefully controlled and injected in proportion to rpm and load.

Diesel power output is controlled by fuel injection pulse width, and the timing of the fuel injection event is carefully timed to ignite at the correct moment but not detonate too soon. When you add propane, it is flowing as long as the boost is above 8 psi, even when the intake valve is open and long before the correctly timed fuel injection event, so it can cause detonation in certain conditions, which is really bad for a diesel.

The plus side is it's always cheaper than diesel fuel (propane currently $1.99/gal here) and when towing my 21,000 lb trailer up and down 4200 ft mountains it saved me about 7 or 8 gal of diesel while consuming just under 2 gal of propane.


One can also convert a gas engine to diesel, a friend of mine is running a propane powered rock crawler. It uses a mixer, which replaces the carb. While it probably increases fuel economy, the main advantages in rock crawling is you don't get fuel pickup problems in the fuel tank at extreme angles, and the engine idle RPM can be dropped from about 800 RPM to just under 200 RPM.
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Old 13-01-2015, 12:11   #13
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Re: LPG mixed with diesel engine

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Originally Posted by Cadence View Post
Insane idea for a boat. Dragster, container ship, stationary gen. set a good idea. Just the weight of the LPG tank of any size would be prohibitive on a boat. I'm sure you only intended this as a brain teaser.
They have spun 'glass tanks that are very lightweight. They'll also remove a lot of weight from your wallet.
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Old 13-01-2015, 12:43   #14
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Re: LPG mixed with diesel engine

Wow, I hadn't thought about the massive propane leak you could get inside of the boat too, heck with the motor, you could blow the whole darn boat up.
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Old 13-01-2015, 15:58   #15
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Re: LPG mixed with diesel engine

I did no realize diesel was that expensive in Queensland.
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