Running on gas

I’ve been making a few enquiries over the last few weeks on the practicalities on running on gas.

It would seem that two types are available that would be suitable to LGV’s. CNG (Compressed Natural Gas) and LNG (liquefied natural gas).

I discounted CNG as supply in the north of England doesn’t exist so I’ve followed the LNG route. I managed to pick the brains of an engineer who has converted trucks to run on gas. (i can’t seem to find that much relevant info off the web)

Anyhow it would seem that although it’s possible to run a truck on 100% gas it has 2 big disadvantages. The engine has basically to be redesigned to run as a petrol engine, spark plugs, ignition system etc. Then when it runs it has the characteristics of a petrol, no torque. However, if you run it with a mix of gas and diesel the engine needs little modification and the response from the engine is identical although a little quieter. It’s typical to run on a mix of 40% diesel and 60% gas. The MPG figures for the vehicle will remain the same.

The cost of conversion is around £2000 (bit more if the air tanks need moving etc.) although on top of this is the price of the tank. As LNG is stored at -160 degrees these are a fortune, between £5000 and £8000 depending on there size.

So anyhow I sharpened my pencil and started doing a few calculations. I based it on a vehicle returning 8 mph and covering 1500 miles a week. (roughly what I do although I‘m only getting 7mpg out of my present truck)

Diesel £0.80 litre or 3.64 gallon
LNG £0.28 litre or £1.27 gallon

1500 miles @ 8mpg = 187.5 gallons.

Running on the 60/40 mix the truck would use 112.5 gallons gas (£142.88) and 75 gallons of diesel (£273)

Weekly fuel cost running on mix - £415.18
Weekly fuel cost running on diesel - £682.50

The annual saving would be £20’000 so the payback period would be 6 months.

The network of LNG suppliers include Whitwood, Lymm, lesmago, J24, J9 to name a few so no big hardship there… So where’s the big catch?

The principle differences in the fuels are the calorific values and the burn characteristics (can’t remember the exact terminology at the mo but I’ll try to keep it straightforward)

Calorific value - relates to the amount of energy the fuel can release

Burn characteristics - relate to how fast the fuel burns

When fuel is ignited in the cylinder it burns progressively and has a ‘flame front’ which spreads through the cylinder consuming the fuel as it goes (have you ever set light to a puddle of petrol and watched as the flame travels over the surface). The greater the fuel volatility the faster it burns and the quicker that the energy is released.

Engine design is usually tailored to the fuel characteristics. Highly volatile fuels are generally used in short stroke engines because the fuel is burnt quickly and by using a short stroke there is less work to do once the fuel has burnt (energy is released only while the fuel is burning and the mixture is expanding pushing the piston down, once it’s all gone any further work done must get it’s energy from somewhere else - another cylinder) but because it’s only a short stroke there is less torque produced for the amount of energy released.

Lower volatility fuels take longer to burn so are used in long stroke engines where a greater torque can be developed for the amount of energy released. As a rule of thumb - short stroke=more power, long stroke=more torque.

The possible catch here is that gas is highly volatile so it will burn quicker and in a long stroke engine that could mean a reduction in power. To overcome this would be fairly simple (technically) by using more gas to release more energy but this would need more air so you would be working at higher turbo pressures - not ideal for longevity. Also using more gas would have a marked effect on the consumption figure.

Overall, I would say you would probably see a reduction in power and torque figures (although not as much as a full gas conversion) and the mileage would probably suffer as well. To try and put a value on this work your figures out on 4mpg and factor in some extra maintenance and see how it looks then.

hope this helps

Jules

Not quite the same but…
6 years ago we had a 13 ton merc converted to run on a mix of lpg/diesel. Overall the running costs stayed pretty much the same, but the power output from the engine increased dramtically. Before the conversion, when going up the M6 to scotland over Shap etc, it was a constant up and down the box, whereas with the conversion is was more of a case of hill, what hill?!!
However, you can’t squeeze a pint out of a quart, and the conversion rapidly took its toll. Blown head gaskets, injector nozzles wearing rapidly, and massive cylinder bore wear. The wagon was eventually scrapped out due to a completely worn out engine, which wasn’t viable to replace.
Don’t know what the long term effects of running on cng/lng are, but definately don’t go diesel/lpg!!
West Transport, in derbyshire, run a load of ERF’s converted to gas, not sure which type though.
Tebay truckstop at j38, M6 also has a gas fill up point, but never looked to see if its lng or cng.

dean36014:
West Transport, in derbyshire, run a load of ERF’s converted to gas, not sure which type though.

I’ve seen these too - they’re type EC127, which I think from reading somewhere is built from scratch as a gas-powered version and has a Detroit Diesel engine adapted by the manufacturer at the time of construction to run on either CNG or LNG. I would think Caratrans’ fleet of gas-powered ERFs is also of this type?

Feathers Diesels of Bradford converted a lot of Scania 113s to gas for one of the supermarkets

strangely, if you look at them second hand, they fetch no money at all which i suppose tells it’s own story.

I seem to remember, they had a bit of trouble with them, and some drivers refused to take them out.

renaultman:
I seem to remember, they had a bit of trouble with them, and some drivers refused to take them out.

Extreme overheating I believe.

Apparently it was so bad the d ivers actually t ought the cab was on fire.

I’ve driven CNG powered dustcarts and they feel no different to a normal truck.
We used to fill up at a gasometer in the borough.
Although I seem to recall they had reliabilty problems but as anyone whose driven a dustcart will tell you - they all do!

cool solutions in hull run their lorries on gas they do a lot of euro work as its run by the people that had nipperess.

give them a ring and ask them.

they’re type EC127

This engine was,indeed a Detroit,and was made in very limited quantities.

A few years ago,I used to visit the ERF factory in Sandbach,on a regular basis with ■■■■■■■ parts,and recall asking the guy in the engine stores what percentage of engines were put in their trucks at the time,and it was something like,90% ■■■■■■■■■■ Perkins,and 2% Gardner.

The Detroit engine was a trial engine to see how it compared with the others.Not very well by the quantities sold.

Ken.

Quinny:

they’re type EC127

This engine was,indeed a Detroit,and was made in very limited quantities.

Yes, the only gas-powered ERFs I’ve ever seen are those operated by West’s and the batch that Caratrans operate, alongside some CNG Scania 113s. Although I assume only a very small number of CNG Detroits are in service in the UK I have read that CNG is a popular fuel for transit buses in North America, so perhaps it was initially developed with that market in mind?

Quinny:
A few years ago,I used to visit the ERF factory in Sandbach,on a regular basis with ■■■■■■■ parts,and recall asking the guy in the engine stores what percentage of engines were put in their trucks at the time,and it was something like,90% ■■■■■■■■■■ Perkins,and 2% Gardner.

Interesting little tidbit, thanks.

There’s nothing wrong with CNG as a fuel, per se, but like all fuel systems the engine and installation needs to be designed for the fuel used otherwise it won’t last/goes wrong.

The Feathers Diesels conversions were probably for the Safeway job which had no end of trouble, why?..because it was a diesel engine and installation so it didn’t cope with the extra heat generated.

The US transit bus CNG option has several things going for it. Firstly there is the pollution control aspect (even though the US has not signed up to the Kyoto accords - big middle finger held up to the rest of the world ) transit buses spend all day in town so a cleaner fuel improves the air quality in the urban environment. Second, the push for CNG was implemented with a new vehicle so a new engine and a proper installation resolves the excess heat problem. Also, even if the engine was based on a diesel motor it wasn’t a conversion job but a properly developed and engineered evolution of the original.

My personal opinion is go for one or the other as a factory developed option, but I would avoid conversions or mixing systems

Jules

About 10-12 years ago, the Burlington Northern Railroad (which was #2 or #3 in the states at the time) used a 2-locomotive consist which ran primarily on CNG, with a small amount of diesel used as the ‘pilot fuel’ to ignite the mixture. The ran with a full cryogenic CNG car to provide the fuel.

They found that CNG did, indeed offer more power, but also caused problems with the motor internals. At the end of the test, the opted to not continue, and the equipment was converted back into regular diesel locomotives.

ACC or the Co-op as its more commonly known run gas powered cat engined foden alpha`s from alfreton.
There dual fuel i.e when the gas runs out they switch over to diesel. You want to try pulling 24 plts of spuds in a fridge over the a66… while its on gas . It seemed to rob 30 or 40 bhp from what was only a 345 anyway
Ever been overtaken by a tractor?