LPG fumigation in diesels

[Tony From West Oz Vice Chairperson of WARFA Find all posts View Profile Close Tony From West Oz]

Re: LPG fumigation in diesels

Hello Adam

Yes, there is a LOT of inaccurate information available about how things work.
You can google Natural Rubber Biodiesel and find over 200,000 websites warning about the "Natural Rubber" fuel lines used in most pre 1993 vehicles.
Natural Rubber was NEVER used in automotive fuel system, petroleum products degrade natural rubber the same as biodiesel does.

You can go to many LPG web sites that will tell you that typically a Diesel engine only burns 75% of the diesel fuel injected, the rest goes out the exhaust. LPG Makes more of the diesel burn.
What a load of bunkum!
If a diesel only burns 75% of it's fuel then a petrol engine must be just as bad because we ALL know that diesel engines get better economy than petrol engines. That would only happen if petrol engines were pumping out lots of unburnt fuel like they claim a Diesel does.
How long would a catalytic converter (Diesel or Petrol) last if 25% of the fuel was going out the exhaust pipe unburnt?

In my mind, the correct answer has to do with the questions:
Why does a diesel engine typically get much better fuel economy and produce less power than a petrol engine of the same displacement?
Does a Diesel engine ever achieve "Stoichiometric Combustion" with injected diesel fuel or is it always running Lean?
If the answer is that a Diesel always run lean could a gaseous fuel such as LPG be included into the air to use some of this unused Air to produce extra power?
If you got rid of the injection system on your diesel and converted your diesel engine to run on 100% LPG (Spark plug required and probably lower compression) coming through the turbocharger mixed with air at the correct stoichiometric ratio, what do you think would happen?

Tilly,
I'll have a go at your quiz. Is there a prize? Perhaps a 20 litre container of the liquid you left with me a year or so ago. Mmmmmm.

1. The diesel engine has a better thermal efficiency than a SI engine. A SI engine of the same capacity can deliver a significant increase over the diesel engine because it can dump in bulk fuel and, despite the very low efficiency at that condition, it will pump out significantly more power. A petrol engine operates at a stoichiometric fuel/ air ratio. If it runs rich or lean, the efficiency drops further.

2. The only time that a CI engine could possibly achieve a stoichiometric fuel / air ratio would be if it were adjusted to over-fuel at maximum throttle. At that condition, the engine fuel efficiency drops and partly burned fuel appears in the exhaust as soot. At ALL times, a correctly adjusted CI engine should run LEAN.

3. Yes, that is the advantage of LPG fumigation, to provide additional fuel which does not cause soot production, resulting in increased engine power. Use of LPG does NOT increase the engine efficiency, but it can increase engine power output (more fuel is used to achieve this).

4. Diesel engines converted with spark plugs and a gas carburettor are commonly used on gas pipeline projects. They use an engine produced as a diesel, for the strong build of the engine components and use spark plugs to ignite the stoichiometric air / fuel ratio provided by the gas carburettor. It can provide similar power levels to similarly sized engines designed as SI engines, but the fuel efficiency drops to that of SI engines. Turbo chargers allow more fuel to be introduced to the combustion chamber because there is more air in the compressed charge air, resulting in an increased engine power output.

Did I win the prize?

When can I expect the 20 litres of your nectar?

Tony

[Captain Echidna Senior Member Find all posts View Profile Close Captain Echidna]

Re: LPG fumigation in diesels

So the increase in range is not due to better diesel combustion, it is because there is an extra fuel tank?
Is adding an extra fuel tank a better proposition of getting extra range?
I guess if you really want to get money from the government you could always join the army reserve

[Guest Close David]

Re: LPG fumigation in diesels

Wait!
I want a crack at this too!

How long would a catalytic converter (Diesel or Petrol) last if 25% of the fuel was going out the exhaust pipe unburnt?

Not very Long. Cat's run at very high tempratures and are sensitive to excessive/unburnt fuel in the exhaust gas stream. Any significant amount of unburt fuel causes them to overheat and melt. when you consider these things are are mainly made of ceramic and titanium, it would take a lot of heat to make that melt but it certainly does happen. Turbo cars can be overfueled at the top end to reduce the onset of detonation and this excess fuel can have the effect of melting the cat if the overfuel condition is held long enough.

Why does a diesel engine typically get much better fuel economy and produce less power than a petrol engine of the same displacement?

I believe this has a lot to do with the way the engines are set up and the actual engines in question. Typically Diesel engines have been much simpler designs than petrol engines. Pretty much all the technology that has gone into diesel for years is Turbo'ing. Petrol engine design on the other hand has given them multiple valves, multiple cams, variable timing of ignition and cams, all sorts of electronic management and every other benifit to make power and economy possible. Diesels typically have been set up for economy or longevity. A lot of the efficency of a diesel comes from the timing of when the fuel is injected and the compression ratio of the engine.

When we now look at the latest developments of the Diesel where they are incorporating these same technologyslike used in spark engines into CI engines ( like the latest BMW's) Diesels can make MORE power and economy than petrol engines of the same capacity. If one looks at what they are doing in the European hot rod scene with Diesels, even basic design 1.6 & 2.0L cars are giving similar capacity but much more developled petrol engines a real run for their money. In the states, Plenty of mods are available for "Pickup" trucks which will enable them to produce 500+ Hp with nothing more than a plug in engine management controller and a Bigger exhaust. When these guys get serious, they can easily run 1000Hp trucks as every day drivers and without laughing gas.

You can get big numbers out of petrol engines, but not with petrol. Once you get to a certain HP per cubic inch, you have to start going to alcohol or other fuels because petrol will only allow you to go so far.
If one looks at drag racing for instance, Petrol cars, even when bottle fed, only go so fast and that so fast is pretty well down the line of overall speed. Alky cars are much faster and run similar capacitys and equipment to cars limited to petrol. With diesel, you can get much higher specific power outputs on " Pump fuel" where the same limitation is quickly exceeded with even high octane petrol. The fastest Diesel engined car still only runs regular Biodiesel not some exotic racing fuel.

When taken to the limit, Diesels can make more power than a petrol engine because the final limitation is the fuel. You can only put a certain amount of fuel in a given capacity engine. Because diesel has a higher energy content and can run higher compression, at the razors edge, diesel wins.


Does a Diesel engine ever achieve "Stoichiometric Combustion" with injected diesel fuel or is it always running Lean?

Again, I believe it depends on the engine.
Some Diesels are set up so they never recieve the maximum amount of fuel they are capeable of burning. Other engines may be set up to produce maximum power at the cost of some efficency.

If an engine is set up so it can achieve an over fueled condition, somewhere in the fuel air curve between lean and over fueled there must be a perfect Stoichiometric ratio achieved if only momentarily in practical use. In this case, the answer would be yes, it can achieve a perfect fuel air ratio and NO, it is not ALWAYS running lean.

If you got rid of the injection system on your diesel and converted your diesel engine to run on 100% LPG (Spark plug required and probably lower compression) coming through the turbocharger mixed with air at the correct stoichiometric ratio, what do you think would happen?

You'd be wasteing a perfectly good Diesel engine??
Aside from this, I can only see that the engine would run the same as a petrol engine. The design of the engines proper isn't any different, its just the fuel, and the way it is fed.

Turbo'ing gas engines works well for the opposite reason it works on diesels. LPG has a higher calorific value but a lower energy rating. As such, you need to put more LPG into an engine to get the same amount of energy as petrol BUT, gas can run at higher compression ratios which can lessen the power deficit through efficency.

While I believe that turning the pump up on a diesel would produce more power than fumigating it, in this case, that does not meet Toms requirement of running a cheaper fuel. In the economy stakes, making bio and having the wick turned up on the engine would be the soloution but if memory serves correct, I believe Tom has space restrictions at his abode so again this isn't practical in his circumstance.

OK, now I'll wait to see if I get a good mark and extra credits or a smack over the kunckles with a ruler.

[tillyfromparadise Senior Member Find all posts View Profile Close tillyfromparadise]

Re: LPG fumigation in diesels

Tony from West Oz is the Grand Prize first place Winner!

Everything Tony posted is correct according to my understanding. The only way you will get a normal Diesel to run at stoichiometric is to over-fuel it so it is belching lots of black smoke.
I will e-mail your prize within the fortnight


Captain Echidna is the first runner-up
You are correct, there is no free lunch. LPG is NOT a catalyst and does not make the other 25% of the fuel burn. you get more power with LPG because with LPG you can put more total useable fuel into the engine

David is the second Runner-up
A Catalytic converter would not last very long if any substantial amount of raw fuel were going out the tailpipe.
Turning the pump delivery up will typically result in an increase in power. The new Mussos can achieve a 13% power increase with no visable smoke.

The following information is from this very informative article
How a Diesel Engine Works - Diesel Motor Basics – Diesel Power Magazine

When the displacement is the same, the diesel engine produces only about two-thirds the horsepower of the gasoline engine. This poses a question: Why is the power output lower even though the combustion pressure is higher?
Since combustion is an oxidation reaction, there is a specific weight of air that will completely oxidize one gram of fuel without leaving excess oxygen. This weight of air is called the stoichiometric air/fuel ratio. The gasoline engine operates with an air/fuel mixture very near stoichiometric.
This is due to the fact that a mixture much leaner than stoichiometric is difficult to ignite in a gasoline engine with a spark plug, and an extremely rich ratio is very inefficient. The mixture is supplied to the gasoline engine by a carburetor or fuel injectors in the manifold and is well mixed and nearly homogeneous.

In the diesel engine, the fuel is injected into the combustion chamber near the end of the compression stroke and ignites spontaneously. This is responsible for the combustion sound that a diesel engine generates that is music to the ears of everyone who reads this magazine. As mixing between the fuel and air occurs, burning continues. This process is very heterogeneous (since the fuel and air are mixed in a combustion chamber it is not as uniform as in a gas engine that has the mixture created prior to entering the cylinder head).
Soot is formed during combustion because some of the fuel burns with insufficient oxygen, and the combustion of the fuel is not completed. As additional fuel is injected, more and more soot is produced. Therefore, the air/fuel ratio of the diesel engine must always be leaner than stoichiometric to prevent excessive amounts of smoke.
For this reason, a modified, high-output diesel will blow black smoke because it is fueled for power alone with no concern for soot generation. The smoke-free diesel has less fuel present in the cylinder than in the cylinder of the gasoline engine, and diesel power is therefore reduced in comparison. Older, naturally aspirated diesel engines can use only about 70-80 percent of the fuel employed by a gasoline engine with the same swept volume and still avoid black smoke."

[Captain Echidna Senior Member Find all posts View Profile Close Captain Echidna]

Re: LPG fumigation in diesels

Why does a diesel engine typically get much better fuel economy and produce less power than a petrol engine of the same displacement?

I thought it was compression ratio. By injecting the fuel at top dead centre and not compressing it, this means a higher compression ratio is possible. (If you run a high compression ratio in a petrol engine you risk the fuel catching alight while the piston is going up, rather than waiting for the spark. burning fuel pushing the piston down while it needs to go up is not good for power or much else)

So there is a lot of excess air in the combustion chamber. When the fire is lit, it burns, gets bigger and pushes the piston down, same as a petrol engine. There is also a lot of excess air in there (at low throttle) which a petrol engine does not have, which gets hot, causing the air to expand, and push the piston down, the heat of the combustion is also contributing to power, not just the burning of the fuel, so there is power coming from 2 sources as such, not just one.

Mind you I guess this is what Tony refers to as "The diesel engine has a better thermal efficiency than a SI engine"

As for less power, Power is determined by tourque and RPM. as the air heating it is a slower process, it means a diesel cant rev like a petrol engine, so has less "power events" per minute, does not burn the same amount of fuel, cant take in as much air to burn with the fuel, so less power.

AS for gas engines having less power than petrol ones it comes down to 2 factors.
Petrol enters the combustion chamber as a liquid, not taking up much space. (it turns to a gas in the compression stroke as things the air gets hot due to compression) Gas takes a bigger volume, so displaces air on its way in. Less air to burn means less power.
Lpg burns more slowly. Unless you are going to make up some special igniton system (which will mean the car cant run on petrol again) it is dificult to get gas ignition spot on.
There are ways to get this power back, but it will mean the car cant run petrol again.

My 2c

[Guest Close David]

Re: LPG fumigation in diesels

From the BanksPower site:

Diesels designed specifically for passenger cars are likely to be both more powerful and smaller than today’s gasoline engines. Look for light duty diesel crankshaft speed to increase, engine weight to decrease, and performance per liter to increase by another 50 percent or more! It’s all happening now.
What will these changes mean to performance?

Diesels already equal gasoline engines in horsepower per liter.

Diesels have twice the torque per liter, and diesels can deliver 20 to 40 percent better fuel economy than comparable gasoline engines. Suppose future diesels are lightened to increase crankshaft speed while reducing maximum torque output. Since a diesel already has so much torque, such a revision might only have 150 percent of the torque of a comparable gasoline engine while its horsepower would also rise to nearly 150 percent of the gasoline engine. The lighter weight would also let the diesel accelerate even more quickly and be just as desirable for vehicle handling characteristics … and all on ordinary No. 2 diesel fuel.

Because enthusiasts have been conditioned to think of gasoline engines when it comes to performance, the idea of diesels may still be difficult to accept, but consider a few facts. Most race cars use alcohol, not gasoline today. Those race cars that do use gasoline use special high-octane racing gas not available at ordinary gas stations. As long ago as 1952, the car that won the pole at the Indianapolis 500 was a turbocharged diesel. Diesels have since been rendered uncompetitive at Indy by rules changes. The fastest pickup truck in the world is diesel powered. The fastest gasoline-powered vehicle in the world (a streamliner) holds the record at 344 mph, and a diesel streamliner is being built to challenge that record. A diesel pickup is being built to challenge Corvettes and Porsches in endurance racing, and diesel-powered vehicles hold the world’s fuel economy records. Diesels are at the forefront of setting new records and of advanced vehicle development.

From Green car Congress

Peugeot Will Go to LeMans 2007 with a Diesel

15 June 2006

Peugeot will enter the 2007 Le Mans 24 Hours race with a new car—to be called the Peugeot 908—powered by a 5.5-liter V-12 HDi diesel engine equipped with a diesel particulate filter system.

Peugeot expects the engine to deliver more than 515 kW (690 hp) of power and more than 1,200 Nm of torque.

Try getting Torque like that out of a <350 CI petrol engine !

[zigparacingtadpole Senior Member Find all posts View Profile Close zigparacingtadpole]

Re: LPG fumigation in diesels

Boy am I glad I havent been near the instrument of the devil for a day or so. That'll learn me for quoting from sales brochures.

[Knudsen Biofuels Forum Newbie Find all posts View Profile Close Knudsen]

Re: LPG fumigation in diesels

Hello Adam

Yes, there is a LOT of inaccurate information available about how things work.
You can google Natural Rubber Biodiesel and find over 200,000 websites warning about the "Natural Rubber" fuel lines used in most pre 1993 vehicles.
Natural Rubber was NEVER used in automotive fuel system, petroleum products degrade natural rubber the same as biodiesel does.

You can go to many LPG web sites that will tell you that typically a Diesel engine only burns 75% of the diesel fuel injected, the rest goes out the exhaust. LPG Makes more of the diesel burn.
What a load of bunkum!
If a diesel only burns 75% of it's fuel then a petrol engine must be just as bad because we ALL know that diesel engines get better economy than petrol engines. That would only happen if petrol engines were pumping out lots of unburnt fuel like they claim a Diesel does.
How long would a catalytic converter (Diesel or Petrol) last if 25% of the fuel was going out the exhaust pipe unburnt?

In my mind, the correct answer has to do with the questions:
Why does a diesel engine typically get much better fuel economy and produce less power than a petrol engine of the same displacement?
Does a Diesel engine ever achieve "Stoichiometric Combustion" with injected diesel fuel or is it always running Lean?
If the answer is that a Diesel always run lean could a gaseous fuel such as LPG be included into the air to use some of this unused Air to produce extra power?
If you got rid of the injection system on your diesel and converted your diesel engine to run on 100% LPG (Spark plug required and probably lower compression) coming through the turbocharger mixed with air at the correct stoichiometric ratio, what do you think would happen?

Hi.
My first post in this forum is just registered.
I'm sorry not good for English writing please correct me if you lose understanding.

I can not read the whole thread, but would you like to illuminate some of what you write.

``
If you got rid of the injection system on your diesel and converted your diesel engine to run on 100% LPG (Spark plug required and probably lower compression) coming through the turbocharger mixed with air at the correct stoichiometric ratio, what do you think would happen?
´´

I have evidence of the following.
Volvo B10 (lying down, 10-litter bus engine)
Spark plug mounted, without opening the engine. Compressed air to breathe drill cuts out while the diesel nozzle holes were made into spark plug holes.
Ignition fixed at 5 degrees AFTER TDC. (This was their patent.)

Result:
VERY much cleaner than the date from that time. I do not want to wonder if it is still cleaner than the current requirements. (I have the information somewhere in my archives.)

Less consumption, due to the high compression and ignition timepoint 5 degrees after TDC.

Higher torque @ less RPM, due to ignition time.

Significantly fewer vibrations and noise.

As I see it, it was ONLY +++++ when the gas was available. Diesel is more prevalent in Europe. (More tax money in complicated systems for cleaning gasoline and diesel engines.)

The engine mentioned had no filters or cathelysator.
The change of oil was prolonged, significantly.
Oil is not consumed / spendt, it is the additives that is consumed and the oil is soiled. Which does not happen so fast with gas operation.

Best wishes
Henrik