Repowering from Gas to diesel

[HT32BSX115]

Re: Repowering from Gas to diesel

Ayuh,.... I wonder what the price tag is on that little Gem,.... I'm guessin' $20,000.00 Plus....

Without the drive, 'n transom assembly of course...

Yeah. NOTHING VW Diesel, is anywhere close to cheap!

 

[Glaspar_Fan]

Re: Repowering from Gas to diesel

It's interesting how much VW has gotten around. I had a VW powered Dodge. Yup, the first two years of the Dodge Omni used a VW engine. A sales guy mentioned that to me when we had the car in for it's first 3K mile check up. Thought he was nuts, but looked and there was the VW embossed on the intake manifold. Someone else later said it was the same as they put in the Audi 100LS. Great engine.

John

 

[Fleetwin]

Re: Repowering from Gas to diesel

Salacia,

Have you considered converting your Petrol engine to run on CNG (Compressed Natural Gas)? I hear it is popular in the UK. Since it is trailered, fuel should not be an issue.

I DO ADVISE AGAINST LPG (Propane/Butane) in a boat. Those two "puddle" (Heavier than air) CNG does not "puddle".

Your GM 3.0L "Industrial" engine is offered by GM as a CNG use engine already.

 

[HT32BSX115]

Re: Repowering from Gas to diesel

I DO ADVISE AGAINST LPG (Propane/Butane) in a boat. Those two "puddle" (Heavier than air) CNG does not "puddle".

JUST like gasoline huh?...........gasoline vapors puddle just like propane and butane (all are heavier than air). That's why you must use a bilge blower prior to starting.


Yes, you can use CNG, but tanks large enough to go anyplace would sink the boat and/or not leave you any room for people or gear!...........and composite tanks would cost more than the boat is worth.

Most boats with the 3.0L engine are usually underpowered already............... The power output by going from gasoline (approx 115,000 btu/gal) to propane (91,000 btu/gal) would be reduced considerably.......... Butane would be close at a little over 100,000 btu/gallon

Propane will generate about 2500 btu/cu-ft........ but Natural gas is about 1030 btu/cu-ft ............It would be a a REAL DOG on natural gas!!

Diesel by the way is about 140,000 btu per gal

The best engine to use would be a 1.9L VW TDI. Evidently Mercruiser flywheel housings and couplers are available......and since they do build a marine version you could probably buy the parts to build an engine using an automotive TDI 4 cyl engine.

They're probably rated at around 150 hp at 4800 RPM .......right where an Alpha likes to run.. and you'd probably have no problem getting it out of gear without an "ignition" (torque) interrupt system. Running it a 600-700 RPM idle, since it has electronic fuel injection one could probably come up with an interrupt of sorts that would work (and not kill the engine)

 

[QC]

Re: Repowering from Gas to diesel

The power output by going from gasoline (approx 115,000 btu/gal) to propane (91,000 btu/gal) would be reduced considerably.......... Butane would be close at a little over 100,000 btu/gallon

Propane will generate about 2500 btu/cu-ft........ but Natural gas is about 1030 btu/cu-ft ............It would be a a REAL DOG on natural gas!!

Diesel by the way is about 140,000 btu per gal

Dude, like my struggles with steam engine torque, you're missing it on this one. You're assuming that it is only possible to inject or draw some limited amount of fuel in just because the density is lower. Why can't I put twice as much propane in and get more power? Fact is you kinda can. The only reason gaseous fuels might result in lower power is air displacement, buuttt they can be higher octane and allow higher compression ratios and actually increase power. The btu comparison is important for cost, but not for calculating output capability. Diesels don't automatically have higher power because the fuel is higher energy per unit. Same discussion. Output is how they are optimized (tuned etc), not necessarily about density. In NASCAR they now run E10 I think it is. They get poorer MPG due to the density drop, but they are making slightly more power due to the increased octane and associated compression increase. Both can apply to the fuels you list as well.

 

[HT32BSX115]

Re: Repowering from Gas to diesel

Dude, like my struggles with steam engine torque, you're missing it on this one. You're assuming that it is only possible to inject or draw some limited amount of fuel in just because the density is lower. Why can't I put twice as much propane in and get more power? Fact is you kinda can.

One absolutely can.........and I really do get it. If someone were to engineer and build an LPG or NG engine for a boat they would certainly build an engine that would take advantage of direct injection, higher compression ratio and/or supercharging. Doing that would approach higher efficiencies and higher HP output. But it's not something a "backyard" mechanic can do which sort of describes most "home-modifiers"..........

Using the highest tech LNG system would be good too........... the fuel tanks would be smaller. (but don't try to buy an LNG tank for a recreational boat though. Not only is there NO USCG/DOT approval for one, but none exist.....and if they did, they would probably cost DOUBLE !

I found one that holds 46 gal of LNG. Full, it's about 400lbs! The stuff on NG efficiency I found indicates that even when you design an engine ON PURPOSE to run on NG, (according to Detroit Diesel) it still takes nearly double the fuel to go the same mile (or hour) ............. So that 46 gallon LNG tank is approx equivalent to around 25 gallons of diesel fuel in it's aluminum or (very light)plastic tank

There is work being done on big ship natural gas fuel etc (you probably already know about that!)

Currently, for recreational boating/cruising, diesel or gasoline is really the only option........and diesel is the absolute safest.

NASCAR they now run E10 I think it is. They get poorer MPG due to the density drop, but they are making slightly more power due to the increased octane and associated compression increase.

With E10, you can build an engine that will get the "same" mileage as an engine running on gasoline. The difference in energy content is nearly insignificant. (E10: 111,000 btu, Gas: 115,000)

I believe they've also have tried using E85 for racing....don't know how that went...........

 

[QC]

Re: Repowering from Gas to diesel

My post wasn't in support of any alt fuel for pleasurecraft, for sure. Only that btu content, and power loss are not synonymous. In my work, when we talk "efficiency" we count btu's. So a nat gas engine, and a diesel could be the same if they burned the same btu's for a specific power output and time period. It is usually written as BSEC (Brake Specific Energy Consumption). Volume is a different discussion, as is power.

I found one that holds 46 gal of LNG. Full, it's about 400lbs! The stuff on NG efficiency I found indicates that even when you design an engine ON PURPOSE to run on NG, (according to Detroit Diesel) it still takes nearly double the fuel to go the same mile (or hour) ............. So that 46 gallon LNG tank is approx equivalent to around 25 gallons of diesel fuel in it's aluminum or (very light)plastic tank

I deal primarily with LNG and CNG in my daily job. LNG volume is a very complicated discussion as temperature is a huge part of the volume discussion. CNG too, but yet another discussion. There are definitely power output reductions (power density) when it comes to comparing a heavy-duty diesel and a spark ignited conversion of that same basic engine. Comes back again to octane believe it or not, and knock margin. Detroit Diesel is probably the least familiar with this. Cummins and Caterpillar the most (in US).

But comparing any low tech gasoline engine (our marine engines, especially carb'ed ones) to it's capability on nat gas or propane, there will be no real power change if done properly. Even with most backyard hacks. You are dead right about direct injection capability. I just reacted mostly to the power output being related to btu content. That's not a reasonable way to approach the discussion as the simple solution is you just put more in

In fact, our friend from the UK here, is really concerned about BSMC (Brake Specific MONEY Consumption). Not much else

 

[HT32BSX115]

Re: Repowering from Gas to diesel

In fact, our friend from the UK here, is really concerned about BSMC (Brake Specific MONEY Consumption). Not much else

And in this case, he only has 1 or 2 real choices.......... Sticking with what he has or going to a currently available diesel. Unfortunately anything else will probably not ever pay off . All of us at the "end" of the consumer chain are pretty much stuck with what's economically available....

I just reacted mostly to the power output being related to btu content. That's not a reasonable way to approach the discussion as the simple solution is you just put more in

I think I am agreeing with you!.. If you look at the actual cost per BTU, many of the fuels are similarly priced ($/BTU). (diesel is a little more than gasoline......Propane is a little less (per gallon) but the Actual dollars per BTU are not all that far off. (excluding transportation, storeage, production, tax, and market etc costs)

And yes, it *shouldn't* matter how you cram the BTU's into the engines, Thermal efficiency of an internal combustion engine is not necessarily related/dependent on the fuel type.

 

[QC]

Re: Repowering from Gas to diesel

Agree that ^^^^^^^