CNG and LPG conversions

[kennythewelder]

They are too worried about cow farts.

Yea. It reminds me of southpark.

 

[sewlow]

My Dad & Uncle owned 32 cabs between them amongst a fleet of 200.
At one time, 30 years ago, they all ran on CNG.
Dad was one of the first, if not THE first inspector of CNG installations in the country. He was in the first class offered to get that ticket & alphabetically, he was the first on the roll-call.
It was a government program. CNG is controlled by the government, NOT the oil co.'s. Therefore, the cost stays pretty consistant. No fluctuations due to market demands, or just palin outright greed on the part of the oils companies.
The government promised to build the fill-stations if the cab co.'s would commit to converting. This is why they went with CNG as opposed to LPG.
I've had several vehicles running on CNG. Both ex-cab winter beaters & a couple of 8600GVW square bodies.
But, as this was more than 'a few' years ago, they were all carbureted. How they manage to be utilyzed on a F.I. system, I have no idea on the specifics.

Anyways, on the CNG systems I'm sorta familiar with, there are only 2 moving parts
The rotary switch to go from regular gas to CNG, & what's called a Disipitator Plate. A rubber bellows that sits on top of the carb, inside the air-cleaner. The air-cleaner needs to be modded some.
There's also a little brain-box that alters the timing. Both CNG & LPG have higher octane ratings than gasoline. Around 130.
The vehicle's timing would be advanced (a lot!) via crank-timing to run the alternate fuel. That brain-box then retards the timing when switching to gasoline.
A propane system works in a similar manner.

CNG always remains a gas. The tanks require high pressure fills to be able to have enough fuel to get any distance. Because of that high pressure required, the tanks are h-e-a-v-y! Thick walled. Like a 1/2" thick! Two big guys ain't picking them up! We'd use an engine hoist to re-n-re 'em.
Most of the cabs were full-size Chevys. They'd have one tank in the trunk. The one tank would take up 1/2 that space.
I had 2 in my trucks.
But here's the major problem with CNG. Limited range. Those 2 tanks in my trucks would only get me about 200KM's per fill. ...or about 120 miles. That fill was at a cost of around a whole $9.00! IIRC, $11.00 was the most a fill ever cost me. Woo!
But, because of the limited number of CNG fuel stations, a dual-fuel system was required.
For the cabs, this wasn't such a big deal as most of the stations were fairly common in densely populated areas. But head out on the road outa the city & the stations became fewer & farther between. Many times, greater than that 200km range.

LPG, when compressed, turns into a liquid. It requires less pressure than CNG in order for it to liquify. Consequently, the tanks are lighter. Smaller, too.
Being in a liquid state, it has the volume that allows for greater distances to be driven.
A friend has an '89 4x4 Chevy 3/4T long-box on propane (dual fuel) He has two LPG saddle tanks & a single under the box. Still enables him to be able to carry a camper. With that amount of LPG & 2 'regular' gas tanks, he can go from Vancouver to Calgary without refueling. A distance of almost 800 miles!

A vehicle can be converted to run on straight propane. Engines can be built specifically to run on it. Because of that high octane, an LPG-specific engine can run compressions of 13-1 or higher. They can make big power, too!
Another of my buddies has a 401 in a Jeep Cherokee, pushing 500hp on propane. Not a dual fuel system though. Straight ptopane. The prob with that is, if he's out in the bush & he runs outa propane, he's kinda up a creek. It's not like he can grab a gas can of fuel from another vehicle or some hermit living out in the bush. He carries a 30lb BBQ tank, just because.

The cost of propane doesn't stay consistant either. I've seen it got for .17/liter. I've also seen it at .85/liter. Seems to be specific to the seasons & supply & demand.
But it is a whole lot easier to find.

Dual fuel systems are also a comprimise.
Because of the need to be able to run both CNG or LPG along with gasoline, they are never quite the optimal set-up for the alternate fuels.
Either way, both dual fuel systems or straight LPG conversions are not about mileage. It's about the cost per mile.

Apologies for the novel! The morning caffiene kicked in!

 

[R422b]

Many good points. (To many to quote)
As to availability i do my 100 to 200 miles a day within a 50 mile circle ( HVAC service calls) and there is 1 station right in the middle where i pass several times a day.
cng is quite popular here. Most highway mantenance trucks use it, some fellow HVAC mechanics also use it and even quite a number of passenger cars use it.
As to pay off time my calculations show it would be well under 1 year. If i could get the tanks for 600$ making the whole system 1000$ ( i know a mechanic that has several just have to check dates and prices)

 

[R422b]

I apreciate sewlow,s post. I didnt think about the range difference between lpg vs cng.
My most miles are in the heat of the summer when lpg is cheap. But cng is always cheap. So i guess i have some deciding to do.
Also i can afford new lpg tanks but not cng. Also cng has some business tax advantages that i am not shure lpg has.
So much to learn so little time.

 

[sewlow]

With the dual fuel CNG, you WILL lose power. As long as you respect that, there's no problem. It's like driving a 6 cylinder as opposed to a V8.

 

[R422b]

With the dual fuel CNG, you WILL lose power. As long as you respect that, there's no problem. It's like driving a 6 cylinder as opposed to a V8.

That shouldnt be a problem for me. My transmission will just last longer. ☺
I guess i better find out what price i can get tanks for. The new cng tank prices are as much as the rigs i drive are worth. So its used cng or lpg for me. Maby someday i will be able to afford a new cng conversion but not now.

 

[R422b]

I have contemplated building a 3/4 ton suburban with a lpg only built motor with a strict focus on efficiency, and a t56 trans. I dont know how a t56 would handle dragging around a 7000lb + rig constantly though.

 

[R422b]

I think lpg is out
It looks like 5.348 gallons of lpg equal 1 gallon of gas. So it would have to get amazing mileage to ever pay off.

 

[R422b]

Ok it looks like with my likely future work truck (a gift from my Grandpa) a 3000 dollar cng conversion would pay off in 30 months. ( i dont like the idea of driving a certain 4 letter brand v10 truck for that long.) So i guess i should probably just look for diesel suburbans. Or 4bt swap one. And run on fry oil.

 

[454cid]

I guess i better find out what price i can get tanks for. The new cng tank prices are as much as the rigs i drive are worth. So its used cng or lpg for me.

I mentioned it before, but I'll say it again just in case you missed it, since you're looking at used CNG tanks... They DO expire. They are dated, and it doesn't matter if they've been used or not.