# Do LPG powered motorhomes have a market?



## LPGMotor (Oct 1, 2010)

Hi,
I run an LPG car conversion businessand am interested in finding out if there is a market for LPG powered motorhomes.

First of all I must say I don't know too much about the motorhome scene and would be very interested to find out more.

What engines are commonly found in motorhomes?
What sort of MPG do you expect from btoh petrol and diesel?
What sort of mileage do people do?
How long do you keep your motorhomes?
Does anyone have an LPG powered motorhome? andif so what system does it use? Where was it converted? How muc did it cost?

I hope I am not breaking any forum rules. I am not advertising my services, just trying to find out if there is a need within your community.

I look forwards to your replies.

Regards,
Shaf


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## Jezport (Jun 19, 2008)

All modern european motorhomes are diesel so cannot run on LPG. Some American RVs are large petrol engine powered and many are converted to run on LPG.


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## KSH (Apr 18, 2010)

Jezport said:


> All modern european motorhomes are diesel so cannot run on LPG.


They can http://www.chilterngascars.co.uk/cars/lpgdiesel.htm


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## GEMMY (Jun 19, 2006)

I can't use the chunnel if I did. Tesco vouchers would have no meaning. 8O :lol: :lol: 

tony


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## teemyob (Nov 22, 2005)

*Market*

Massive Market

Lots of Petrol US RV's out there.

When they get Diesel/LPG right, even bigger market.

I have a Toyota Previa I am thinking of getting converted.

TM


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## TDG (May 26, 2009)

KSH said:


> They can http://www.chilterngascars.co.uk/cars/lpgdiesel.htm


The technology for burning gas in very large marine diesels is complex so I would think applying it effectively to automotive engines is very difficult
Looking at their website, it seems to me to imply that they are not selling a system to burn only gas but one that uses it as a pilot fuel to try and improve the diesel oil combustion.
Sniff.........sniff........sniff, is that snake oil I can smell :?:


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## LPGMotor (Oct 1, 2010)

TDG said:


> KSH said:
> 
> 
> > They can http://www.chilterngascars.co.uk/cars/lpgdiesel.htm
> ...


That is correct. A diesel engien cannot be converted to run on just LPG. There would be nothing to ignite the gas.

But LPG can be injected at about a 20% mix. It acts as a catalystfor the diesel making it burn better, as well as burning itself. Gives better power and torque. You do also save marginally on the fuel costs. On normal cars the problemis the cost vs benefit. It would cost around £1,500 to convert so would takea long time to make your money back.

Could be more benefit for motorhomes though. I imagine the fuel consumption is somewhat worse than a diesel mondeo. And of course the LPG canbe used for cookers etc.


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## skiboycey (May 21, 2009)

Most of the big 3.0 litre turbo diesel motorhomes get about 20mpg in everyday use so anything that helps this would certainly be worth looking at. Even a 20% mix with no increase in power would save around 10p a litre in fuel costs if my calcs are correct which is a big 'if'... If the power were increased by the use of lpg mixed into the diesel then presumably mpg would be improved somewhat, as well.

A couple of thing occur to me.

1/ If a viable system of LPG mixing for larger diesels exists then why don't fleet operators use it? If anyone could make the capital outlay repay itself quickly it would be somebody running a vehicle 18 hours a day, 7 days a week... Or maybe they do?

2/ If LPG ever gets truly popular it will end up getting taxed the same as any other road fuel and the price differential will disappear. Granted this has not happened in all the years it's been used but I'm a cynic about governments and their rapacious need for money to fund their reckless spending programmes and look at diesel that was once cheap compared to petrol and is now more expensive!

Perhpas Mr LPG could enlighten us on the above and give some realistic performance/consumption/cost figures? If it stacked up I'd imagine there'd be a market especially as many motorhomes already carry re-fillable LPG tanks for use in cooking/heating which could presumably be used to fuel the engine as well...

Cheers, Mark


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## TDG (May 26, 2009)

LPGMotor said:


> ...../That is correct. A diesel engien cannot be converted to run on just LPG. There would be nothing to ignite the gas. .... .


Oh yes there is :!: 
The heat from compression would be adequate to ignite the gas given the correct fuel / air ratio- in just the same way as it ignites the diesel oil  
However, it's almost impossible to control other than at very low power  What is done on very large engines is to inject it directly at very high pressure and in conjunction with variable valve timing, variable valve lift and variable geometry and sequential turbocharging it is possible to have very effective gas or diesel operation on these engines over the full power range which can be up to 70,000 Kw 8O 
I have never heard that pilot gas injection can improve the combustion efficiency of these engines but with their specific consumption now approaching 135 grams/ Kw / hour giving thermal efficiencies of >50% perhaps it's a solution to a problem that isn't worth solving :?: 8)


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## T25Mash (Apr 16, 2008)

LPGMotor said:


> Hi,
> Does anyone have an LPG powered motorhome? andif so what system does it use? Where was it converted? How muc did it cost?


Our VW T25 was converted almost as soon as we imported it. The boxer engine isn't the most efficient design and usually returns about 23mpg. We have since upgraded to a 2.1 petrol but kept the LPG system.

The 50 litre tank runs for about 200 miles, but without the reduced costs we would never have had the use out of the van. Luckily being a simple 4 cylinder engine our conversion was less than four figures and has paid for itself many times over.

Small price to pay for losing one of the wardrobes to fit the tank.

Its such a shame the costs are creeping up, when first converted 5 years ago we paid 32.9p/l now it is frequently 70p/l.

Was nice to be in Belgium 18 months ago and pay 32 cents a litre, cheaper than my house gas.

Matt


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## raynipper (Aug 4, 2008)

All the time we owned American RVs with large 7 litre V8 petrol engines I argued against having any LPG conversion done as you would never make sufficient savings to recover the initial outlay.

Even with an increase of 50% i.e from 10 mpg. to 15 mpg. You would have to do a colossal mileage to recover the £2000 to £3000 installation costs.

Ray.


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## Mrplodd (Mar 4, 2008)

I cannot for the life of me see any way you could convert a Diesel engine to run solely on LPG.

A Diesel engine works by injecting the (liquid) fuel directly into the combustion chamber at the appropriate moment, Although it happens very quickly this fuel burns progressivly, thats why Diesel engines produce higher torque figures than a comparable petrol engine (the fuel does NOT explode in either engine it burns very quickly) It is also injected as a liquid (in very very fine atomised spray) not as a gas.

In a petrol engine the air and fuel is ingested into the engine together, in a diesel engine just air is drawn in, that air is then compressed (at a ratio of about 20 -1) in the combustion chamber. That heats the air to a very high temerature at which point the diesel oil is injected over a finite period of time, the very hot commpressed gas ignites the diesel fuel to give a controlled burn. 

Now we all remember from our Physics lessons that you cannot compress a liquid but you can compress a gas can't you?? 

Thats why you can inject diesel fuel into the collossaly high pressures that are present in a diesel engines combustion chambers. There is no way you will be able to get a gas to a high enough pressure to get it into the engine fast enough. That compression would also take a huge amount of energy which, as a by product, will also produce huge amounts of (waste) heat. 

Back to schoolboy Physics " Energy is never lost or gained, it is only ever transferred" Where will all the energy needed to compress this gas come from ???

So back to the original post.

Nice idea but as has already been stated, no-one has yet come up with a (commercially viable) system that enables you to run a Diesel engine (correct terminology is actually "Compression ignition" engine as opposed to a petrol engine which is "spark ignition" ) on LPG 

As someone has previously stated if there IS a system why dont fleet operators run it ???


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## Zebedee (Oct 3, 2007)

LPGMotor said:


> [It acts as a catalyst for the diesel making it burn better, as well as burning itself..


Nope! 8O

If it is a catalyst it will remain unchanged throughout the chemical reaction. >> See here <<

Can a highly flammable gas can act as a catalyst in a burning process?

It would be a good trick for it to catalyse and burn the diesel before being burned itself in a separate reaction.

Without knowing a lot more detail about the process I have to wonder if TDG and the other sceptics are correct?

Dave 

(P.S. No accusations intended, but snake oil is a good catalyst for parting fools and their money! :wink: :lol: )


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## TDG (May 26, 2009)

Mrplodd said:


> Nice idea but as has already been stated, no-one has yet come up with a (commercially viable) system that enables you to run a Diesel engine (correct terminology is actually "Compression ignition" engine as opposed to a petrol engine which is "spark ignition" ) on LPG


Oh dear :!: 
You had better tell the shipowners who are very happy running their MAN -BW and Wartsila diesel engines on LPG :roll:


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## Mrplodd (Mar 4, 2008)

It may well be that some huge marine engines can be run using some LPG but I am still pretty certain they cannot be run soley on the stuff.

I could be wrong and would be quite happy to admit my error if someone comes up with some proof.

If there is such a system why are not the very large fleet operators (such as Tesco) using LPG only compressin ingnition (Diesel) engines ?? 

Could it be because there is no such engine available for use in road vehicles???


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## Pudsey_Bear (Sep 25, 2008)

Just to add fuel to the fire :lol: :lol: lick me


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## CliveMott (Mar 10, 2008)

Offer a conversion service to Travelworld in the UK. They are probably the UK biggest distributor of american RV,s

c.


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## olley (May 1, 2005)

Mrplodd said:


> Thats why you can inject diesel fuel into the collossaly high pressures that are present in a diesel engines combustion chambers. There is no way you will be able to get a gas to a high enough pressure to get it into the engine fast enough. That compression would also take a huge amount of energy which, as a by product, will also produce huge amounts of (waste) heat.


You needn't inject gas, you could inject LPG as a liquid, there are already liquid injection systems available for petrol engines, although they are fitted into the intake system.

So it would be simple to inject the LPG directly into the cylinder if you wished, although I would imagine valve timing and the like would have to be altered, and whether it would run well or not I have no idea.

Olley


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## nicholsong (May 26, 2009)

I followed Kev's link to Mercury with the following results

They do not show a conversion price.

However they have a calculator and entering my mileage of 4000pa, diesel price of 120p/lt and LPG of 70p/lt the savings per annum came to £63+.

If the conversion is anything like £1000+ it seems that their system is a financial non starter as the opportunity-cost of capital equates to annual saving however long one keeps the MH. Different if one does 10-15,00 miles a year, but there is still the risk of a LPG fuel hike within the amortisation period.

I would be interested in the OP's comments.

USE OF THE SAME TANK TO SUPPLY THE HABITATION SERVICES

I am not sure whether this is feasible since, as I understand, in a motor running on LPG the LPG is supplied to the engine as liquid and is then converted to gaseous form, whereas for Habitation use it leaves the tank in gaseous form. 

Anyway an interesting topic and as always some knowledgable comments.

Geoff


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## Mrplodd (Mar 4, 2008)

The other interesting point is that _"Quicksilver seamlessly blends both fuels"_ note the word blends! it does NOT run the engine fully on LPG. Neither does it state what proportion of LPG to diesel is used. I wonder why not? Could it be that the ratio is so low as to make it not really viable finacially?? yet again I ask, why dont very large fleet operators have their fleets running on this system? perhaps it doesnt stack up cost wise.

There are VERY clever people out there with an eye to making money. As yet no-one has come up with a system to run diesel engines in road vehicles on LPG alone.

If it was possible I am pretty sure some bright spark (sic) would have doen so by now, with LPG being significantly cheaper than Derv the cost savings (IF it was possible) would be enormous.


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## skiboycey (May 21, 2009)

I'm not an expert on this but I'm a pretty good home mechanic so have a good idea how this stuff works...

I doubt any diesel LPG system would work by injecting the LPG to the cylinders. I'd imagine you'd put an injector into the intake plenum chamber (or equivalent), probably post turbocharger and intercooler and then inject a small amount of lpg gas to the air mix. I'd further imagine this very weak mix of LPG and air would now either 'help' the diesel that is subsequently injected to the cylinder to burn more effectively/powerfully or it would just 'replace' some of the diesel needed to run the engine either by the means of the engine management system leaning out the mix by detecting different levels of engine output gasses (presumably if the incoming charge of air is now partly LPG then less diesel will be required to be burnt to produce a given output of Carbon Dioxide etc. and the system would reduce the diesel charge accordingly) OR you'd reprogram the engine management to reduce the volume of diesel injected for a given load/rpm etc. to take account of the gas added at the intake. 

I'd imagine some pretty big problems with knock and octane ratings as LPG is going to burn quite fast and be very prone to pre-ignition as it's such a low fraction but in a weak mixture maybe it doesn't knock? Maybe this is why the blurb said the fuels are 'seamlessly mixed' and why the LPG used is quite low for a given milage?

I'm not quite sure how such a marvelously complex and tuned piece of engineering like a modern direct injection diesel would react to having some flammable gas added to it's charge of incomming air but it seems somebody's claiming to have got it to work. One thing that does occur to me is that maybe if, say, 15% of the fuel is now made up of LPG and, perhaps, 85% diesel I'd imagine the efficiency of the engine (which has been very finely tuned to run on diesel since it's inception on a computer screen) will probably go down. This might not be the case if draconian emmissions limits are not respected by the conversion but this might mean that running an LPG/diesel/air hybrid might return less MPG than you might hope and that might mean the mitigation of price is not as high as hoped. This could be why no big fleet operaters seem to be using or sponsoring the system. If I was making the conversion I'd offer it free to a large user like TNT or the Post Office as the publiciity generated would be so huge and lead to people like ourselves buying it. As this has not happened it probably doesn't work very well!

On the other hand LPG is going to burn hotter and faster than diesel alone so perhaps it acts as a combustion enhancer and helps to burn particulate matter than would otherwise be ejected from the exhaust. I'd have thought chucking a gallon of petrol into a full tank of diesel would achieve the same thing - something we often do in the alps to prevent freezing of diesel in sub -20 degree conditions but you can't push the engines hard when you do this or they'll knock. 

I would think this would be the limiting factor of this technology and might be why it can't be made to work well on small, high compression engines. Don't forget that most large, ship-sized diesel engines are forced induction two-stroke diesels which don't have valve gear in the same sense that road engines do and run low compressions compared with smaller engines which are compensated for by high-powered mechanically forced induction (large superchargers in plain English).

Just a few musings to add to this interesting thread...

Regards, Mark


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## TDG (May 26, 2009)

[quote="skiboycey"...]I would think this would be the limiting factor of this technology and might be why it can't be made to work well on small, high compression engines. Don't forget that most large, ship-sized diesel engines are forced induction two-stroke diesels which don't have valve gear in the same sense that road engines do......Regards, Mark[/quote]
Sorry....the majority of gas diesels are 4-stroke :lol:
PS I don't know of any modern supercharged marine diesel engines :roll:


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## olley (May 1, 2005)

TDG said:


> Sorry....the majority of gas diesels are 4-stroke
> PS I don't know of any modern supercharged marine diesel engines :roll:


Here's one :lol:
http://en.wikipedia.org/wiki/Wärtsilä-Sulzer_RTA96-C

Olley


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## TDG (May 26, 2009)

olley said:


> Here's one :lol:
> http://en.wikipedia.org/wiki/Wärtsilä-Sulzer_RTA96-C
> 
> Olley


No :!: That, and all the others, are turbocharged :roll: 
Supercharged = compressor mechanically driven by the engine
Turbocharged = compressor driven by exhaust gas energy. Typically that can extract the equivalent of circa 30% of the engine MCR  from the exhaust energy and deliver charge air at >3.5 bar pressure. Often there is still enough energy left to have another exhaust gas turbine driving an alternator to provide electrical power for the vessel and even then there is still enough heat left to be extracted to produce low grade steam  
All this for free from the exhaust gas that would otherwise have been sent straight up the funnel 8)


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## olley (May 1, 2005)

Hi I was referring to it being a 2 stroke, for 2 stroke supercharged diesels I can think of two but their both oldens,  

The Deltic which powered a load of our trains and the GM straight six's, both used a Roots blower. The Deltics had one of the best power to weight ratio's of any diesel when they where built. The GM's where a bit odd as they had 4 exhaust valves, even though they were 2 strokes.

Olley


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## skiboycey (May 21, 2009)

The point I was trying to make is that large, ship-sized marine diesels are not particularly comparable with small, high-revving vehicle engines and the technology used to allow them to burn LPG or at least be enhanced by it is probably not comparable.

When I say 'supercharger' I meant any mechanically forced induction which is not a turbocharger. Plenty of two-stroke ship engines use an electric motor to drive the incoming charge into the cylinder via a port in the cylinder wall. Others, perhaps more modern, probably use a turbo and many a mixture of the two. Others have valve gear, at least for the exhaust and some probably work like a conventional four-stroke. In any case an engine designed to operate at about 400 rpm for tens of thousands of hours running on fuel that needs to be heated before injection to turn it from the tarry treacle it comes as to a useful fuel is not going to translate to a camper van engine!

Does anyone really know how the claimed LPG system works other than my guesses above? I'd be interested to know...

Cheers, Mark


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## TDG (May 26, 2009)

olley said:


> Hi I was referring to it being a 2 stroke, for 2 stroke supercharged diesels I can think of two but their both oldens,  ...Olley


They certainly are old :!: 
The Deltics were very expensive to buy and maintain AND the reliability was terrible in marine service and very very few(<10?)found their way into commercial marine operation.
The GMs? Well the Americans don't "do" diesels very well compared with the Europeans :wink: although I have to admit to having has some excellent performance from some 12V92s as alternator engines :wink: However, in that case we didn't have to be worried about the fuel consumption 8O


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## TDG (May 26, 2009)

skiboycey said:


> The point I was trying to make is that large, ship-sized marine diesels are not particularly comparable ....


Agreed :wink: 


skiboycey said:


> Plenty of two-stroke ship engines use an electric motor to drive the incoming charge into the cylinder via a port in the cylinder wall.


Only when operating at <35% MCR... after that the turbochargers supply all the scavange air and the motors shut down



skiboycey said:


> Does anyone really know how the claimed LPG system works other than my guesses above? I'd be interested to know...


On the marine gas diesels, the gas is injected at the same pressure as liquid fuel but of course gas at that pressure can be considered somewhat hairy so there is now a move from the Diesel cycle to convert to the Otto cycle using pilot liquid fuel to ignite the gas injected into the charge air but the control process is quite complex and as you say will not scale down very well :roll: It also requires gas of constant charactoristics to ease the control process. Does Autogas have this :?:


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## Mrplodd (Mar 4, 2008)

Boy hasnt this thread got complicated after such a simple initial question.

Quite an education !!!


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## nicholsong (May 26, 2009)

Well Mr.Plodd you should know 'simple' Qs do not always have a simple answer.

When is the OP going to come back on to explain to all in 'simple' terms how his suggestion actually works???

Geoff


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## grizzlyj (Oct 14, 2008)

Kev_n_Liz said:


> Just to add fuel to the fire :lol: :lol: lick me


From the above

"Performance

Under scrutiny Quicksilver produces substantial improvements in fuel economy. At 1.4/1 substitution Quicksilver averages 30-40% diesel substitution across a full range of loads & work regimes with trucks fitted with Euro 4 or 5 SCR (ad-blu) or EGR technology.

Some older trucks of pre-Euro vintage may see further improvements in performance as fuel efficiency can be improved by the injection of LPG. However any suggestion that LPG can improve general fuel efficiency on newer engines is not borne out in theory or practice. During our own testing substitution ratios achieved are almost identical to those theoretically predicted by calorific comparison.

Because of its unique flexibility Quicksilver is scalable from the largest HGV to smaller delivery vehicles of 35cwt and above, giving fleet operators the opportunity to extend economies through the entire fleet and not just for the hardest working, heaviest vehicles. This enables operators to increase gas tonnage and achieve the best discounts available from gas companies."

Calorific comparison meaning lower mpg?? Don't they contradict themselves there?

And;

"Why does it have such a significant tax advantage over liquid road fuels? 
The clue is in the chemical formula C3H8, LPG is significantly richer in Hydrogen as a ratio to carbon than either diesel or petrol. If LPG could replace all diesel & petrol as a road fuel, it would have the same effect in CO2 reduction as removing 20% of all vehicles from the road."

Mercury fuel systems do inject directly into the cylinder though, which it suggests some competitors do not. Injecting into the air intake presents a fire risk if the intake system is damaged for whatever reason 

Approximate proportions from their tank sizing example;

"With Quicksilver fitted the actual tank capacity required to complete the week would be 600 litres of diesel & 281 litres of LPG."

"At present the government has a 3 year advance agreement with the industry that prevents duty levels from closing more than 1 pence per year"
"In Germany the government has given a 20 year promise to maintain current duty levels to allow a stable LPG industry to grow, there is pressure on the UK government to move in the same direction."

In answer to what is LPG on an older thread, from the same site;

"What is LPG? 
LPG or Autogas as it is most commonly known when used as a road fuel is 99% propane (C3H8) and 1% butane when bought in the UK. The 2 gases are blended at different ratios according to the prevailing temperature in the region that it is to be sold in."


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## olley (May 1, 2005)

TDG said:


> They certainly are old :!:


The GM's where still being fitted to Transtainers when I worked at Felixstowe Dock 20 years back, so not that old, they were also the best Diesel I ever worked on, beautiful engines, far better than perky's, cummins, cats or the crap rolls royce which was the worst.

Olley


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## TDG (May 26, 2009)

olley said:


> ...or the crap rolls royce which was the worst...Olley


No arguement there :lol:
PS My experience with them was that they generally blew up in such a big way that it was often not possible to work out what had failed to initiate the blow up but when you could, it was either a bottom end bearing or a turbocharger oil seal :x


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## TDG (May 26, 2009)

Kev_n_Liz said:


> Just to add fuel to the fire :lol: :lol: lick me


As a qualified (marine) diesel engineer, having read their blurb it still sounds a bit like a snake oil recipe to me and one which I don't understand much better than Jane's physio-babble :lol: 
One thing that intrigues me is, does their system result in an engine that still operates on Diesel Cycle or is it converted to run on the Otto Cycle because if it's the latter, it will inevitably be less efficient than the former  
Alternatively, perhaps they should consider using the bicycle :lol:


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