Gasoline and diesel fuels...

[Externet]

If ~10 drops of gasoline are added to one litre of diesel fuel, to say a 1:1000 ratio; what different behavior can be expected in a diesel engine ?

 

If ~10 drops of diesel fuel are added to one litre of gasoline, to say a 1:1000 ratio; what different behavior can be expected in a gasoline engine ?

 

If no appreciable/measurable effects, would 5:1000; 10:1000 ratios show something; and what would it be ?

[Enthalpy]

10 drops per litre, I say: no effect.

 

Gasoline in Diesel isn't very harmful. Diesel engines are rather tolerant even without tuning; I ran mine with 1/3 rapeseed oil. They need fuel with low ignition temperature, reasonable viscosity and no particles; recent engines must run with low fuel-to-air ratio, which precludes vegetable oil.

 

Better: my Diesel's user's manual tells I can run on plain kerosene, and that in cold winter, I can add up to 20% gasoline in Diesel oil to thin the fuel.

 

Diesel oil in Gasoline is more of a worry, because Diesel must ignite easily and gasoline must not. Diesel oil would raise the cetene and lower the octane numbers. So don't exaggerate this one, since early ignition destroys an engine quickly.

[decraig]

Fracturing crude oil is not exact art. An assay would find heptane and octane already present in diesel fuels. And probable in quantities greater than one part per thousand.

Edited December 22, 2013 by decraig

[Dekan]

Mulling over the above posts, I wonder why all our internal combustion engines don't run on diesel.

 

Consider the advantage of the diesel engine - the fuel doesn't need electric sparks to ignite it. It goes off by itself, by mechanical compression. So there's no need for spark plugs, with their associated complex, and likely to malfunction, electrical circuitry.

 

Why don't we use diesel engines more - is there something against them?

Edited December 23, 2013 by Dekan

[arc]

Diesel is a breed of its own, fewer repair shops and part availability, it would have to scale up to compete with gas. And that would dive up its price, taking away one of its advantages while making everything delivered by a diesel more expensive. Gas was so much more available in the past, small engines on farms and the first tractors were all gas. Same in marine engines, there were more outboards than even inboard gas engines, and there were a lot of those. It took many years for diesel to make inroads into those smaller applications, starting with the need to move larger machines.

 

The really cool applications were in aviation starting with the Packard radial in 1928-29. The Germans though took it to a new level with the Jumo 205. prior and during WWII

 

Image furnished by Tennen-Gas who has no connection to me or this post.

If you had to choose between highly explosive aviation fuel or the safer kerosene it was an easy choice. Especially in war planes.

I used to work with a guy that was training to be a navigator in b-24's, he said they were terrified of blowing up in mid-flight during training. The tanks were over filled by the ground crews so they vented as the planes climbed, he said the planes smelled of gas fumes.

They had many solenoids that operated things like bomb bay doors, rattling from the shaking plane. He said he was flying in formation somewhere here in the states and the plane to their right just blew up.

Diesel is a breed of its own

[Enthalpy]

Diesel engines avoid the ignition hardware but need high-pressure injection pumps (plus separate valves now) that are expensive. The higher chamber pressure also demands a stronger construction. The net result is an engine a bit more expensive at identical power.

 

Power per volume unit is now the same, per mass unit nearly the same. And because Diesel uses its fuel better, thus saves refueling stops, Diesel cars win endurance races presently.

 

Diesel engines are but absent from individual cars in teh US, but make half of this market in Germany as a gut feeling, and are dominant in France. This results much of which technology national car makers have developed and how governments favoured them.

 

The vehicle fleet must also fit the available fuels. Oil distillers can adapt their production much, but within limilts. The trend is to exploit heavier oil (Alberta, Orinoco...) that gives heavy fuels more easily, favouring Diesel in the future.

[ASG]

enthalpy, you're using rapeseed oil with an improvement?

[Dekan]

Just going back to a basic point - if diesel engines can ignite their fuel by compression, can't gasoline (petrol) engines do it too?

 

I mean, why do petrol engines need spark plugs?

Edited January 22, 2014 by Dekan

[Danijel Gorupec]

Otto-cycle engines need spark plug (or any other 'external' mean to light the fuel mixture in the right moment) by definition. The spark plug is one of things that makes them 'otto cycle'.

 

You could build a diesel-cycle engine that uses petrol, but this would be difficult because very high pressures will be needed.

 

You could make some other type of engine that uses petrol, while does not have a spark plug (gas turbine perhaps?)... What I want to say is that by saying "petrol engine" you tell nothing about engine construction, only about fuel it uses. If you want to refer to construction details, you should use terms like otto-cycle engine, diesel-cycle engine, gas turbine...

[Enthalpy]

If diesel engines can ignite their fuel by compression, can't gasoline (petrol) engines do it too? Why do petrol engines need spark plugs?

There is no strict need to ignite lighter petrol distillates with a spark and heavier ones by air compression, at least when designing a new engine, but it helps a lot. Once the engine is designed, there is little choice.

 

Heavier distillates like Diesel oil have a lower autoignition temperature, which means that compressed air ignites them more easily. Gasoline would demand a higher temperature, hence a stronger compression, as Danijel wrote. For gasoline, a spark is easier.

 

Why not always a spark? Because Diesel oil already injected in the cylinder would self-ignite during the compression. A purposely-designed engine would have a very low compression ratio and efficiency.

 

So the stronger compression and efficiency - with the costs associated with oil pumps and sturdy engines - fits the Diesel ignition scheme and the heavier distillates, and the smaller compression with spark ignition fits gasoline.

 

Traditionally, Diesel engines were also less responsive and heavier. Combined with higher cost but efficiency, they equipped lorries and taxis. This situation evolved 30+ years ago in Europe where improved Diesel engines equip small cars.

Enthalpy, you're using rapeseed oil with an improvement?

This was with a Citroën Cx bought in 1987. A very nice turbo-Diesel, but of older design, with a pre-chamber where the mix keeps much fuel proportion even at idle. Rapeseed oil destroys a modern Diesel engine within days.

 

Zero modification to the car. I put 1/3 rapeseed oil in 2/3 Diesel oil one after the other in the tank. Car like older Mercedes with a stronger Bosch in-line injection pump run with pure rapeseed oil; mine can't cope with the higher viscosity. Maybe kerosene or gasoline would allow more rapeseed oil.

 

No worry in winter; I had -15°C there and the engine started smoothly. I've had no worry with the fuel filter neither, despite the car had run 240Mm on Diesel oil before, then 110Mm with the mix. An unmodified older Mercedes ran >450Mm on pure rapeseed oil. The seals knowingly resisted rapeseed oil, while biodiesel needs adequate ones.

 

I've observed the same consumption by volume, which means little more by mass - only 6L/100km at 160km/h on montainous highways, for an old big car, excellent design. The exhaust gas smells distinctly; one sees less fumes (allegedly because vegetable oil brings oxygen atoms in the molecule, more possibly because it contains no carbon rings), and the Mercedes driver has observed perfectly clean cylinders.

 

The noise got quieter. All clac-clac by the old engine disappeared with 1/3 rapeseed oil, sounding more blob-blob. Possibly the higher viscosity dampens some movements, say at the rings - only a hypothesis. For sure, the engine ran cooler; I noticed it as the cooler was nearly destroyed, and the oil has 20°C less than with pure Diesel oil.

 

Some excellent websites existed in German, where users shared their experience; search for Pflanzenoel Diesel.

 

If one wishes to try: your car, your risk. I tried with mine, that's enough. Do check at least the pre-chamber (needs pre-heating before start) and the injection pump.

[Delbert]

Mulling over the above posts, I wonder why all our internal combustion engines don't run on diesel.

 

Consider the advantage of the diesel engine - the fuel doesn't need electric sparks to ignite it. It goes off by itself, by mechanical compression. So there's no need for spark plugs, with their associated complex, and likely to malfunction, electrical circuitry.

 

Why don't we use diesel engines more - is there something against them?

They produce crap from the exhaust which is harmful to human health - to be non scientific about it.

 

In fact I wouldn't advise anyone to purchase a modern (or old) diesel engine car. If for no other reason than the DPF device (Diesel Particulate Filter) now fitted to these vehicles to remove aforementioned crap. The DPF is problematic and expensive to replace.

 

If fact I understand there is a growing industry if offering to either remove said DPF, or, following recent legislation, doctor the DPF such that it looks like a functioning DPF, but is in fact simply an empty can!! Bugger human health.

[Dekan]

I suppose petrol engines may have caused more harm to human health by using leaded-petrol, and producing lead-laden crap from their exhausts. Aren't diesel fumes lead-free?

[Delbert]

I suppose petrol engines may have caused more harm to human health by using leaded-petrol, and producing lead-laden crap from their exhausts. Aren't diesel fumes lead-free?

I can't recall the date, but I think you will find lead was removed from petrol fuel for cars about 25 years ago.

 

I was waiting for someone to suggest crap emanates from all internal combustion engines. Yes it undoubtedly does, but with the abandonment of the internal combustion engine not happening anytime soon, dealing with it is the way to go. But with evidence pointing to diesel as being quite prolific, to the point whereby it is often clearly visible from the exhaust of a non DPF vehicle, it's a good idea to improve the situation.

[Enthalpy]

The Diesel particle filter is used on every recent Diesel car in Europe, which may amount to 50% or even 70% of the fleet depending on the country, and is not known as a big headache. It's similar to a catalytic exhaust for Otto engines.

 

Lead spewed out in our environment by gasoline then is there to stay. No more in the atmosphere, fortunately.

[Delbert]

The Diesel particle filter is used on every recent Diesel car in Europe, which may amount to 50% or even 70% of the fleet depending on the country, and is not known as a big headache. It's similar to a catalytic exhaust for Otto engines.

I think you will find that DPF functionality is not like a catalytic converter. Inasmuch as I understand a catalytic converter converts pollutants directly, converts them to CO2 and H2O. Whereas I understand a DPF filters out particulate matter into a filter - not unlike the filter in your vacuum cleaner. What happens when the filter is full, one might ask? Well, apparently the system goes into what's called 'regen'. During this the engine fuel mixture is enriched, causing neat fuel to enter the exhaust. This ignites the filtered particulates in a hot DPF and hopefully cleaning out the filter.

 

Apparently one of the problems is that 'regen' might not take place during short journeys, whereby the engine doesn't run for long enough and the DPF doesn't get hot enough. The likely end result being a blocked filter and a non functioning engine.

[Dekan]

Apparently one of the problems is that 'regen' might not take place during short journeys, whereby the engine doesn't run for long enough and the DPF doesn't get hot enough. The likely end result being a blocked filter and a non functioning engine.

Yes, I read recently that diesel cars aren't recommended if they're mostly used for short trips, where the DPF doesn't get hot enough. But is this an urban myth. It certainly doesn't seem to be referred to by manufacturers of diesel cars. I've got a very nice diesel-engine car myself. And have used it with complete satisfaction, for three years - while only making short urban journeys of a few miles a day. So far, there's no sign of the engine becoming non-functional due to a blocked filter.

 

How soon can the filter-blockage be expected to occur - will there be any preliminary symptoms one should note. Like pedestrians coughing as one drives by, perhaps?

[Delbert]

Yes, I read recently that diesel cars aren't recommended if they're mostly used for short trips, where the DPF doesn't get hot enough. But is this an urban myth. It certainly doesn't seem to be referred to by manufacturers of diesel cars.

Well, I don't think manufacturers would mention it if they wanted to sell the cars!

 

I've got a very nice diesel-engine car myself. And have used it with complete satisfaction, for three years - while only making short urban journeys of a few miles a day. So far, there's no sign of the engine becoming non-functional due to a blocked filter.

I suppose it depends on the age of your car, as it's only in recent years that diesel vehicles have been so fitted with a DPF.

 

Should one be so fitted, I understand there'll be a dashboard light indicating whether a filter is getting full and regen is overdue.

 

How soon can the filter-blockage be expected to occur - will there be any preliminary symptoms one should note. Like pedestrians coughing as one drives by, perhaps?

The filter is to prevent pedestrians from coughing!

 

But as above, I believe there'll be a dashboard warning light - your vehicle handbook should describe and reveal all.