Long Life of Gasoline Engine Running on CNG

Your sample space is too small. I had similar conversations down in South America and the conclusion was just the opposite, the engines required rebuilding/overhauls much more frequently then their gasoline only counterparts.

NG has little has very little lubricity, heat removal capability, and lacks the additives that are blended into gasoline. The intake valves receive very little cooling inherent in the evaporation of the gasoline charge, the exhaust valves don't get the benefit of the additives that are in gasoline, plus the NG acts a degreaser on the cylinder walls, none of which contributes to engine longevity.

The end result is that unless valve seat inserts and specially faced valves are used, the valves burn up and/or the seats recede into the heads, resulting in frequent head/valve train replacements.

It could be that your engine-savvy cabby was using some form of oil injection scheme similar to that used in two cycle motorcycle engines along with a "special" crankcase oil; unlike the cabbies in SA who just do the fuel system conversion and save half the cost of gasoline and then scour the streets looking for junked engines to be used as spare parts bins.

The cabbie did said that most other engine model have shorten life span probelm, only the particular model he was using has long durability , it was Proton Iswara ( Mitsubishi Orion engine). I wonder if this engine has characteristics that make the difference.

My only personal experience is with a mid-50's stationary installation. It was a converted straight-6 truck (Reo, I think) engine driving an air conditioning compressor, running on natural gas. I estimate it ran about 36 hours a week for 20 weeks a year. At 50 MPH equivalent that would be 36 x 20 x 50 = 36,000 miles/year. It lasted 21-22 years (700K+ miles) before being replaced with more modern electric compressors. It was overhauled after about 10 or 12 years, so it was probably about worn out when it was retired. I say overhauled, but I don't remember for sure if the rings and bearing were replaced. I do remember that the valves had worn down into the heads like . . ., well, a lot! Of course, that was without hardened seats. Also, we weren't too diligent about oil changes, probably 10-12,000 miles between - it always looked clean .

I'm with you on most of your points, but about acting as a degreaser on the cylinder walls - I would think the solvent properties of gasoline would be worse in that regard than the dry gas?

I know some cities have had 'less that stellar' service from CNG buses, particularly in the summer in hot climates, but I recall Houston having lots of problems in the mid-70's with their diesel buses, too. I suspect the real problem is in the conversion process - all the issues are not understood or are not dealt with. GM's first attempt at automobile diesels comes to mind.

From my personal experience of running engines on propane I have seen that cylinder washdown with vapor fuels is largely a myth. Gasoline is a strong hydrocarbon solvent whereas vapor fuel for the most part are about as solvent like as air.

Every small engine I have ever experimented with and vehicle engine I have had apart that I have ran on propane had a sort of greasy vaseline like layer on the cylinder walls that gasoline engines never get.

From what I have been able to find the primary cause of NG and LPG fuel engines failing was due to them being old pre unleaded fuel type that did not have the hardened valves and valve seats or higher strength alloy pistons that today's vehicles come with stock from the factory.

The only other issue I know of that could wreck and engine with those fuels is gross over fueling while being severely overloaded. When in the right A/F ratios they just don't produce enough heat to be a issue for a gasoline engine parts under normal operation conditions.

I'm coming up on 300K total miles driven on several vehicles over the last 12 or so years and I have yet to ever have a single engine failure directly due to the propane. In fact I have only had one so far and that one was my severely abused and neglected 1987 Mazda B2600 pickup that I bought for scrap for $200 because the engine was already thought to be junk. I don't know exactly what broke yet but its a knocking sound so I suspect a broken wrist pin ring or rod bearing of which that would have happened just as easily if it had been running on any other fuel.

Part of the problem is not all engines are built equal. Most typical light automotive engines are not designed to last compared to their industrial and commercial application equivalents.

For example most vehicles see an averaged running speed of around 50 MPH over their anticipated 200,000 mile life which engine run time wise is only around 4000 hours whereas an averagely maintained industrial engine is expected to make it at least 20 - 25K (35 - 50K is not uncommon) hours before needing a major rebuild.

On top of that a engine properly designed for NG or LPG fuel operation is not built exactly like an engine set up for gasoline. Plus going from there who and how it gets maintained makes a world of difference as well.

My point is running a engine on NG or LPG that is of a lower quality low life expectancy design that was intended to be ran on gasoline and having problems does not suprise me one bit. I rather expect it.

Now that said if the engine was designed for industrial and commercial applications plus setup correctly for NG or LPG fuel seeing million mile plus and 40K+ hour working life spans would not surprise me either.

BTW there are massive low RPM single cylinder flywheel type industrial engines that run in remote locations off of NG that are well known for having been in continuous use for 30 - 50 years (350 - 450K hours running life) without having ever been rebuilt.

There are plenty of diesel engines in boats out there in the 50-60 years old range....My buddy had a single cylinder that once it was started and heated up, the only way to shut it off was to smother it by stuffing a rag into the air intake....once the fuel was shut off(electric fuel pump) it would pull diesel oil from the crankcase through the loose rings and max the rpm's like you were standing on the accelerator....It was a wild ride until he could block the air flow(not as easy as you might think)....lol.....it was cool because I always thought it sounded like the "African Queen", putt putt putt...

Great good load of info !

I wonder also , for the average car, the golden rule for oil change / 5k km is over-done. I have a feeling that this rule was made by engine oil manufacturers to boost sales. I wonder if there is any independent study done to review this rule.This rule is ancient, obviously, much advance has been made since this rule was made .

Imagine, if this rule is revised to say 8k, by the hundreds of millions of car in the world, how much time and resources would be saved !

http://www.edmunds.com/car-care/stop-changing-your-oil.html

Good link, thx!

Trouble is....all the car forums I belong to state the 5000 km interval as if it was an edict from on high! Fact is, a Grand Caravan needs its oil changed (normal oil, not synthetic) at 12000 km. 7500 for mine because it is older. I believe that it does not hurt to follow the manufacturer's owner's manual. Extra oil changes are just dumb...they do NOTHING to improve the life of your engine.

When you consider that only 50% of oil ever gets recycled, (the rest is dumped in fence post holes), the earth really IS more important than a wasted oil change on your engine.

(Hope I get some flames!)

"Imagine, if this rule is revised to say 8k, by the hundreds of millions of car in the world, how much time and resources would be saved !"

Not much would be saved. Right now at 200K most vehicles are reaching the age, 15 - 25 years old, and condition to where the rest of the vehicle is falling apart and not cost effective to repair or keep up.

We have several vehicles in our family that are in the 200 - 240K mile range that have solid running engines that still don't burn oil. The problems are that the vehicles are 20 - 25 years old and everything else is falling apart.

I have no experience with vehicles running CNG but I have had a lot of experience with electrical generators run on natural gas. The problem is the word "natural" and the product varies from location to location depending on where the supply comes from. Reciprocal engines have different reactions to the impurities that are included in the "natural" gas. While the BTU level can be adjusted for, the impurities can really raise havoc with engines. Some places the engines do fine and seem to last forever, other localities, the engines have very short life due either to abrasives in the gas or minerals which will plate out into the combustion chamber and cylinder walls. I suspect the CNG has the same problems. Some areas like SA probably have contaminents which will shorten the life.

I think those NG that come from well directly without going thru liquifaction will have a more impurity. THose that come from CNG has been processed by liquifaction, so it should be much cleaner.

I hope someone can confirm my conjecture.

Do you know exactly which oil was being used? It is possible that it was a modern synthetic long life oil.

Modern Synthetic oils, against old fashioned mineral oils used in similar engines, can:-

a) lubricate the engine better

b) on a cold start are better at getting to remote engine parts at full pressure

c) leave a coating of oil on engine parts far longer

d) when overheated they evaporate without leaving burnt residue

e) can be left in use far longer and therefore are in the end far cheaper than conventional oils.

I have been using such oils since the 80's......on many cars, mostly Diesel engined with a Turbo.....

The only problems that appear to be apparent with petrol to gas fueled (converted) engines is that they are not recommended by the companies that do the converting, to be driven with a heavy trailer on gas, they recommend reverting to petrol only for those trips....usually a simple switch over.

I am sure that when an engine was specifically designed for gas, such worries do not exist......I did read somewhere that gas burns hotter, but whether this is the problem I cannot say, I am a Diesel fan!

I also found tcmtech's comments very interesting here, they appear to lay to rest some of the "urban myth" worries with gas engines.....thanks. Maybe one day in the future for me too....

The cabbie used normal mineral oil, Shell Helix type.

Having worked in the propane and NG fields in the past I have witnessed this same scenario.

When I worked in these fields most of the smaller 5 ton and less sized service and delivery trucks were propane or CNG fueled.

Most of the propane and NG vehicles would go 500K miles minimum with about 10% reaching the 1 million mile service mark before requiring any major work.

The oil change interval was pushed out to 10,000 miles with no apparent issues.

Often the truck bodies and running gear gave out and the engines were moved into other vehicles or remote pump applications.

The gasoline engines usually had severe issues within 100K and the diesels would usually require a major overhaul within 200-300K miles.

In the farm fields close by where I presently live there are a lot of farmers running NG engines on their irrigation pumps and some of them are late 60's models that the hour meters have long since stopped operating.

All of the farmers I have talked to indicate their NG engines last at least 10 years longer than any of their diesel and gasoline engines.

Every mechanic I have talked to state that the propane and NG fueld engines are extremely cleaner inside and have minimum wear compared to gasoline and diesel engines.

Getting 750,000 km of service life of engine from any motor car is unbelievable.

Cars in Taxis do give longer life because Taxi Driver seldom switches off the care when waiting for customer. In Europe I have seen that their heating is on and may be in Singapore, from where this topic has sprung, may be the Drivers when waiting for customer, keep the AC on.

Reason for longer life when engine not being frequently started and stopped - is because the maximum wear of engine happens at start - because of no lubrication.

But again above can be true for petrol or diesel engine. Not with CNG as conventional petrol engine having compression ratios of more than 13 are prone to detonation in Gas Engines.

Detonation increases with:

- Increase in higher hydrocarbons C3 and above. Methane is best fuel for gas engine. This property of gas mixture is defined by a number Methane Number. Higher the methane number better the fuel is.

- Increase in ambient temperature - higher the temperature of gas mix entering the engine - higher is the chance of detonation. Also for each Deg rise in air intake temperature - the exhaust gas temperature increases by approx. 3.7 Deg. Increased gas temperature further results in reduction in life of exhaust valves and turbo etc.

- Higher compression ratio. Safe for any fuel is 1:8 (which holds good for old cars, but not with now a days cars).

- Air fuel ratio. Richer the fuel more chance of detonation. stoichiometric air fuel ratio or leaner fuel can reduce detonation.

- Firing angle, retarding firing angle also helps in reduction of detonation - for this reason large gas engines have detonation detectors attached in heads which adjust firing angle for optimum operation. (advancing the angle improves efficiency but risk of detonation).

Further from above one can conclude that if a gasoline engine is run on propane (LPG) it is still worse for life of engine. As LPG has lower Methane Number.

quality of lube oils does improve the life of enigne but can not reduce or eliminate detonation. Hence I could not justify how the cab could have a long life of engine on CNG. Only reason I can think is that it must be old car (750,000km) having engine with low compression ratio which did not go through repeated starts and stops.

Gas and gasoline engines can be severely damaged by fuel detonation, no doubt of that......but it should never happen, especially on a modern engine with a built in "knock" detector......

Why should you be so worried about it.........?

Correct maintenance and "relatively" modern car electronics are all that is needed........its simply not a big deal anymore.

In case of high compression ratio - electronic will not help - specially in case of cars - reason being that if detonation occurs in high compression engine - you can not change compression ratio. Only you can do is reduce power and will result in lugging or jerks in the cars.

Compression ratio can be changed by keeping exhaust valves opened for longer period - but this provision is not seen in engines (today I was at Auto Expo in Delhi and saw many engines cutouts; Honda, Fiat etc. but did not find any provision of changing valve timings).

As I said member is talking of a particular case of 7 year old car and of Taxi whose engine might not be started frequently - hence long life and it shall not be generalized for all cars on CNG.

Your comments are, especially this and the one before, to put it nicely, very strange.

It is almost as though you only did half of the training course.......some things you know, some you guess wrongly.....

I am unimpressed.

Sorry to be the bearer of bad news, but it is better you know now, before you really make a fool of yourself here.

You may have noticed that I am not the only one who thinks this.....

He has got 18 good answers Andy.... Not too shabby.

To any reader of CR4, do not believe even half of what this person called powersolutionsFBD writes, its simply misleading and often wrong.

If you can sort out the wrong from the right, you don't "need" his posts anyway.......

If you agree (or even disagree!), then the Off Topic (or On Topic!) votes should be added (to any post you feel strongly about!).

These are anonymous by the way....

I see a logic problem here! How on Earth would you not start the engine and still provide taxi service and make miles and miles and miles?

Some taxis start the engine once, if that, in say 24 hours, using changes of driver......the engine remains running, therefore warm.....Cold starts are the killers....

It would be wise to check facts on some of your statements before posting them.

HUH?

I'm giving your post a D-.

There are a few correct things but way more that are wrong or completely the opposite of what you state.

Where did you get your info from being most of what you stated is what I hear from the 'I heard it from a friend who heard it from his neighbor who heard it from the auto store parts desk guys who overheard a conversion between two customers' people who have never actually work with the subjects at hand levels of accuracy.

Isn't it an Octane number, not a Methane number?

Dear Sir,

Hope you are serious. Either please open the text book or search Google and you will find what is Methane Number of Fuel Gas.

Best regards,

Ramesh Kapur

Oh, I am certain that there is a Methane number. In Canada, fuel rated in Octane. Have no idea on how different types of natural gas are rated. So different natural gasses for sale in (wherever you are) are rated by their methane number? Google check..seems they are rated here by Methane number as well...

So octane ratings are used for liquid fuel. Methane ratings are for natural gas and biofuel gas.

Well, learn something new every day!

Hi

I ran a 4G15 in a Miti Lancer (Australia) on gasoline for close to 650,000 Km not a taxi before it needed attention and if it had had regular oil changes before I got it, it would have lasted longer. Chuck the myth of cylinder bore wear away with gas as the reduced carbon build up from the cleaner burning gas is a lot kinder to bores, rings, bearings, oil pump, valve guides, valve seat and valves. Aluminum cylinder heads have hardened seats as standard and suffer little from the dry fuel, dirty air cleaners that have been blown out with compressed air (perforated the filter) cause more damage. But large mileages are quite common in taxis million km is not uncommon as long as the taxi is maintained, regular oil changes with quality oil and air cleaners

Good post. I think 4G15 is the engine of the cabbie I chatted with.

Best I managed was 238,000 Km before the car was stolen off my drive way. A Nisan Primara 1.6. the engine never missed a beat. Correction the starter motor jammed once, a quick clout with a hammer and off she went again.

Often wondered what happened to her.

My son christened it "the skip," I'm not the tidiest person in the world.

Some more fuel for the proverbial fire.

http://www.nytimes.com/2014/02/14/us/study-finds-methane-leaks-negate-climate-benefits-of-natural-gas.html?src=rechp&_r=0