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Old 17-09-2008, 13:24   #1
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Natural Gas Conversion

Hello, I have given up on the idea of converting a diesel engine to electric, due to the outrageous cost fo the conversion, the battery instability and space requirements. I would like to look into a natural gas conversion...

To refresh your memory, I do not yet own a boat, and am a novice, but will purchase either a single or multi-hull sail boat, somewhere between 45 - 50 feet by June. I wonder about the feesability of converting the diesel or gas engine to Natural Gas... Any thoughts?

Blessings, and as always, thank you for all of your thoughtful input.
Karole
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Old 17-09-2008, 14:00   #2
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I may be mistaken and likely am, but I don't think you can store enough natural gas to match an equal volume of diesel to go the same distance.
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Old 17-09-2008, 14:08   #3
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I wonder about the feesability of converting the diesel or gas engine to Natural Gas...
If you convert the BTU's from natural gas (aka propane) and a comparable amount of diesel fuel you can find the energy difference. You can't get more energy than there is. Storage of a large volume of propane will require an exceptionally heavy tank.
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Old 17-09-2008, 16:32   #4
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A mechanic could probably give a better answer, but in short a diesel engine could not be converted to natural gas. A gasoline engine could, and there are probably a number of kits available as well as shops that specialize in conversions - just google for them. The problem with NG, is that it is a lot more dangerous than diesel. It's also probably harder to find around the world; if you're not straying too far then that might not be an issue. Good luck with your boat hunting.

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Old 17-09-2008, 19:17   #5
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How would you get compressed natural gas in a marina? It is much rarer than propane!
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Old 17-09-2008, 19:27   #6
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Energy density

You can see that Diesel has a gravimetric efficiency of 10,942 watt-hours per liter while LNG and propane has a volumetric efficiency in the area of 7,000 Wh/l.

Diesel also has only a very slightly less volumetric efficiency than jet fuel.

So basically, you would have to have a LNG or Propane tank that is 10.9/7 larger or about 55% larger to store the equivalent amount of heat produced from Diesel.

As a side note, look how much larger an equivalent hydrogen tank would need to be 10.9/2.6 or 420% larger. So basically if you have a car that runs on hydrogen its fuel tanks are going to need to be over 400% larger in order to have the same driving range.

Energy densities from highest to lowest: (volumetric/gravimetric)
Fission of U-235 4.7 x 1012 Wh/l 2.5 x1010 Wh/kg

Boron 38,278 Wh/l 16361 Wh/kg

JP10 (dicyclopentadiene) 10,975 Wh/l 11,694

Diesel 10,942Wh/l 13,762 Wh/kg

Gasoline 9,700 Wh/l 12,200 Wh/kg

LNG 7,216 Wh/l 12,100 Wh/kg

Propane (liquid) 7,500 - 6,600 Wh/l 13,900 Wh/kg

Black Coal Bulk =>CO2 6278 Wh/l 6667Wh/kg

Ethanol 6,100 Wh/l 7,850 Wh/kg

hydrazine (Mono-propellant) 5,426 Wh/l 5,373 Wh/kg

Thermite Fe2O3(s) + 2Al(s) -> Al2O3(s) + 2Fe(s)
(mono fuel) 5,114 Wh/l 1,111 Wh/kg

Methanol 4,600 Wh/l 6,400 Wh/kg

Ammonia 4,325 Wh/l 4,318 Wh/kg

Liquid H2 (Hydrogen) 2,600 Wh/l 39,000† Wh/kg

Hydrogen Peroxide 100%
(mono-propellant rocket fuel)
Often used at 30% or 90% and
correspondingly less dense.
when used, not all decomposes
consider this a maximum
1,187 Wh/l 813 Wh/kg
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Old 17-09-2008, 21:19   #7
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Diesels can run on alcohol, gasoline, natural gas, kerosene, fuel oil, biodiesel coal oil, whale oil, darn near anything.
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Old 20-09-2008, 10:09   #8
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Diesels can run on alcohol, gasoline, natural gas, kerosene, fuel oil, biodiesel coal oil, whale oil, darn near anything.
Is this theoretical or have you actually done this? I don't profess any experience in this regard - I can only go from what I've read. From my understanding, you can't just pour vegetable oil in the tank and fire up a diesel - you either need to pre-heat the fuel or you start the engine with diesel and switch to veg oil while it's running. Like alcohol, natural gas has a high (effective) octane rating, so I would think a resistance to detonation would be problematic in an engine that essentially relies on it? As I understand it, to convert a diesel to natural gas, one would need to reduce the compression (by changing the cylinder and/or head) and install an ignition system - essentially turning it into a gasoline engine. While the economies of scale may make this a viable option when converting a fleet of busses or trains, it would be uneconomical to convert the 1-3 diesel engines in a typical cruising boat. Even if you are able to "tune" a diesel to run on NG, there could be a problem caused by the lack of lubricity of NG; the oiliness of diesel fuel lubricates the injection system. If Karole is still interested in pursuing this, she might wish to contact these people - they convert diesels to NG: AEC - Advanced Engine Components Limited
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Old 20-09-2008, 10:28   #9
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Originally Posted by klevalt View Post
I would like to look into a natural gas conversion...

<snip>

I wonder about the feesability of converting the diesel or gas engine to Natural Gas... Any thoughts?
As an engineer I often remind our guys that, "Just because you could, doesn't necessarily mean you should."

Backing up one step in the design process is often helpful to gain focus. The question in this case begs to be answered, "What problem am I trying to solve?"

I presume that the problem you are trying to solve may be. "How to cruise "greener""

In this case I would start with all the things that are "not" green. Starting with a few footprint questions.

- Do I need a 50 foot boat? How many people are cruising?
- Do I need a lot of power? Wooden ships didn't have any engines
- Can I do without refrigeration?
- How much am I willing to pay to be green? The hybrid electric thing is coming. Now it is expensive and there is a lot to work out.
- Do I need to be green now? Go with diesel and repower when the hybrid electric thing is more mature.

Diesel works and works very well. It is a simple engine, plenty of bang for the buck, reliable, and fairly efficient. There's a good reason 99.9% of all cruising boats have them.
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Old 20-09-2008, 12:30   #10
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Propanre is not Natural Gas. Propane is a product of petroleum refining. Natural Gas is just that, a natural product that comes out of wells. Propane is availabe almost anywhere. Natural Gas, actually Compressed Natural Gas or CNG, is available almost nowhere. A few areas that have a high concentration of boats do offer exchange CNG bottle fills. When I checked they were few and far between, however. On the West Coast, seem to remember it was LA, Alameda, and Seattle. Hardly suitable for a cruising boat if you need a fill up. If T Boone Pickens is successful, may find wider availability of CNG filling stations, however

CNG is relatively safe. It's lighter than air thus would probably escape into the atmosphere from a slow leak. A massive leak could possibly get you the right concentration for an explosion but the smell would probably be obvious before it reached a critical concentration. Propane is heavier than air so will settle to the low point of the bilge. Doesn't take much of a leak to get an explosive concentration and a continuing leak will keep adding fuel for the explosion till something goes boom in a bigger way.

CNG was hyped in times past for it's saftety and convenience. Unfortunately, not enough people have adopted it for it to become widely distributed. It seems to be a dieing option as fewer and fewer boats seem to be using it.

As far as use in a diesel, don't know if either CNG or Propane will work. Would seem that detonation would be a problem, however. Biggest problem with both CNG and Propane is energy density as has pointed out in other threads. Also, CNG is under great deal of pressure, SCUBA tank pressures. Where it's conveniently available, it's only available on a bottle exchange basis. Not conducive for the amount needed for propulsion.

Aloha
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Old 20-09-2008, 21:53   #11
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I haven't done it personally

but Caterpillar, Fairbanks-Morse and Wartsila have multifuel engines as well as gasoline/diesl mix engines. These have tha ability to switch from liquid to gaseous fuel instantly.....They are becoming common in power generating plants....they are not seen in Marine Propulsion as far as I know.

Quote:
Originally Posted by Lodesman View Post
Is this theoretical or have you actually done this? I don't profess any experience in this regard - I can only go from what I've read. From my understanding, you can't just pour vegetable oil in the tank and fire up a diesel - you either need to pre-heat the fuel or you start the engine with diesel and switch to veg oil while it's running. Like alcohol, natural gas has a high (effective) octane rating, so I would think a resistance to detonation would be problematic in an engine that essentially relies on it? As I understand it, to convert a diesel to natural gas, one would need to reduce the compression (by changing the cylinder and/or head) and install an ignition system - essentially turning it into a gasoline engine. While the economies of scale may make this a viable option when converting a fleet of busses or trains, it would be uneconomical to convert the 1-3 diesel engines in a typical cruising boat. Even if you are able to "tune" a diesel to run on NG, there could be a problem caused by the lack of lubricity of NG; the oiliness of diesel fuel lubricates the injection system. If Karole is still interested in pursuing this, she might wish to contact these people - they convert diesels to NG: AEC - Advanced Engine Components Limited
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Old 21-09-2008, 05:55   #12
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My motivation is going green, and saving money. Also, I want to retain some semblence of comfort, since living aboard is our desire. I don't think that 45 - 50 ft is so outrageous, considering the downsizing that I will be experiencing. Some sort of conversion would be great, however I am trying to balalnce out the conversion cost with the $ savings and so going green is less the motivation... I can certainly wait for technology to catch up.

I appreciate everyon's input. Please continue to give me your thoughts and ideas.
Blessings.
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Old 21-09-2008, 09:10   #13
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but Caterpillar, Fairbanks-Morse and Wartsila have multifuel engines as well as gasoline/diesl mix engines. These have tha ability to switch from liquid to gaseous fuel instantly.....They are becoming common in power generating plants....they are not seen in Marine Propulsion as far as I know.
The so-called dual-fuel engines seem to be designed specifically for oil rigs and the like, where there's an abundant supply of NG that would otherwise be burnt off on a flame-tower. While burning NG, they continue to burn diesel as a "pilot fuel" - it's just reduced to 1-5% of the total fuel burned. This would result in cost-savings and is ostensibly 'greener'. Note they have a second fuel-injection system (for the NG) and a diesel-injection system that is capable of switching from 100% supply to "pilot" supply. Converting a marine engine, if possible, would not be inexpensive.

I picked this bit out of Wikipedia: "Multifuel engines are designed to reliably operate on a wide variety of fuels, to include diesel fuel, jet fuel, kerosene, heating oil or gasoline. Gasoline should only be used in an emergency because it does not properly lubricate the injector pump. While using gasoline, common practice calls for the addition of at least 1 quart of clean motor oil per 15 gallons of gasoline for proper pump lubrication where available."

Not so easy adding motor oil to Natural gas

I wouldn't give up on the electric conversion completely - I would consider a "hybrid" arrangement. Say you get a cat with 2 diesels. Pull one and sell it, to offset the cost of 2 electric motors and a SMALL battery bank. Use the remaining diesel as a generator only (or sell it too and buy a dedicated diesel genny). The small battery bank won't give you much range, but if it's only to get you into the marina, it should do. Then you can plug it in or let the solar panels charge them. And the diesel would give you the option of increasing your motoring range. Diesel-electric propulsion is considerably more efficient than diesel-only. If you stay away from the complicated (and expensive) marine regeneration systems, you can probably come up with a relatively inexpensive and reliable system. There are likely far more resources out there devoted to converting cars to electric - that might be your best bet for doing a conversion that won't break the bank. Good luck.

PS here's some sites to get you started:

RE-E-POWER Electric Propulsion for Marine Applications
Electrosail
Build Your Own Electric Car out of a Gas-Guzzler
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Old 21-09-2008, 09:52   #14
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Originally Posted by klevalt View Post
My motivation is going green, and saving money. Also, I want to retain some semblence of comfort, since living aboard is our desire. I don't think that 45 - 50 ft is so outrageous, considering the downsizing that I will be experiencing. Some sort of conversion would be great, however I am trying to balalnce out the conversion cost with the $ savings and so going green is less the motivation... I can certainly wait for technology to catch up.

I appreciate everyon's input. Please continue to give me your thoughts and ideas.
Blessings.
Sailing is the original green. Just use your sails. Forget about a diesel.
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Old 21-09-2008, 11:43   #15
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Just throttling back on your diesel saves quite a bit of fuel.
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