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WHat are the advantages of emulsified diesel for ships and land based diesel generators? Why is this technology not used?
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Emulsions of diesel fuel and de-ionised water are used in certain applications, typically in a proportion of around 13% water. Check out PuriNOx, and Elf Petroleum.
The motivation for using a diesel/water emulsion is for emissions reduction. Generally, NOx goes down as the percentage of water goes up, ie, 13% water ~ 13% NOx reduction. There is also a worthwhile smoke reduction, and often a just measurable improvement in SFC too.
Why only a 13% water emulsion? Because any greater than that, and it requires a pumping rate increase from the injection pump and/or larger injector nozzle flow area to maintain rated power. If you make these changes, you can go up to around 50% water emulsion before combustion suffers.
Why is it not used more for automotive applications? Because you need the water percentage to vary as a function of load, and with a response rate rapid enough to follow the load changes. Not possible with an emulsion generated upstream of the injection pump. At light load, you can only support a very low water percentage before combustion suffers.
What marine engines are doing now, is to utilize engine heat to provide distilled water via a condenser, which is then turned into steam which is fed into the induction system to provide humid air induction. This gives NOx reduction capabilities similar to a water emulsion.
PJGD
The motivation for using a diesel/water emulsion is for emissions reduction. Generally, NOx goes down as the percentage of water goes up, ie, 13% water ~ 13% NOx reduction. There is also a worthwhile smoke reduction, and often a just measurable improvement in SFC too.
Why only a 13% water emulsion? Because any greater than that, and it requires a pumping rate increase from the injection pump and/or larger injector nozzle flow area to maintain rated power. If you make these changes, you can go up to around 50% water emulsion before combustion suffers.
Why is it not used more for automotive applications? Because you need the water percentage to vary as a function of load, and with a response rate rapid enough to follow the load changes. Not possible with an emulsion generated upstream of the injection pump. At light load, you can only support a very low water percentage before combustion suffers.
What marine engines are doing now, is to utilize engine heat to provide distilled water via a condenser, which is then turned into steam which is fed into the induction system to provide humid air induction. This gives NOx reduction capabilities similar to a water emulsion.
PJGD
Does it matter whether the water is emulsified or as steam? Does it effect the NOx reduction if you can control the nature of the emulsion?- eg watre droplet size? Do the emulsifiers used by Purinox /Elf effect the NOx reduction adversely in any way?
Emulsified water and diesel is not really new, but the process of keeping the water in suspension has been difficult. Modern common rail injection systems also operate at very high pressures, and internal pump dimensions are very critical. The presence of raw water in the pump can mean instant destruction to metal on metal parts as the water has little lubricity qualities.
Purinox has been relativly successful and their results appear promising. From what I have seen, NOx and PM are both reduced.
Injecting steam into the air inlet tract has also been used for many years with similar results.
Franz
Purinox has been relativly successful and their results appear promising. From what I have seen, NOx and PM are both reduced.
Injecting steam into the air inlet tract has also been used for many years with similar results.
Franz
I agree that modern common rail diesel fuel systems are not tolerant of low lubricity fuels such as water emulsions. This statement may be true for most rotary pumps too. In-line pumps and unit injectors are much more tolerant.
I am not sure what the surfactants are that PuriNox use, but I do not think they affect emissions. There will be a paper from Sandia National Lab on this subject at the next SAE Powertrain & Fluids Conference in San Diego in mid-October.
The droplet size of the water in the raw emulsion is of little importance since the fuel is thoroughly mixed and atomized during the injection process.
PJGD
I am not sure what the surfactants are that PuriNox use, but I do not think they affect emissions. There will be a paper from Sandia National Lab on this subject at the next SAE Powertrain & Fluids Conference in San Diego in mid-October.
The droplet size of the water in the raw emulsion is of little importance since the fuel is thoroughly mixed and atomized during the injection process.
PJGD
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I do not agree with those who have concern about using emulsified diesel fuel on automotive applications. In fact, by adopting lower water content, you can experience almost the same reduction in PM and very low power losses at rated conditions. Moreover, the dynamic cycles show that rated conditions are less relevant in automotive applications.
In large diesel engines the water content can be as high as 40%. One benefit is to allow even more extreme fuels to be burnt such as orimulsion.
The viscosity of these FWEs (fuel water emulsions) can increase significantly. This means that the fuel has to be heated to higher temperatures in order to optimise the viscosity at the injectors.
One of the issues between steam injection and water emulsifiction is ensuring sufficient raw water.
For information on this visit the web sites of the major Large Diesel engines such as MAN B&W, Wartsila and so forth.
Forming an FWE requires a fuel mill and a homogeniser. Some good information on the site of who provide the fuel process systems.
The viscosity of these FWEs (fuel water emulsions) can increase significantly. This means that the fuel has to be heated to higher temperatures in order to optimise the viscosity at the injectors.
One of the issues between steam injection and water emulsifiction is ensuring sufficient raw water.
For information on this visit the web sites of the major Large Diesel engines such as MAN B&W, Wartsila and so forth.
Forming an FWE requires a fuel mill and a homogeniser. Some good information on the site of who provide the fuel process systems.
May be here is some new aspects of FWE.
Let's be a bit more accurate.
There is a significant difference between the fuel-water emulsions in general and the effect of water (or steam) in the engine, specifically on the processes in the cilinder & cilinderhead (burning).
As to WFE generally. Here are two main aspects. Storage and behaviour in the feeding system.
In the storage there are two main difficulties.
The first is stability. Up to my recent knowledge these emulsions has got limited lifetime. The stability of an emulsion depens upon many condition. Temperature and its changes, other materials in the system, mechanical effects (eg. shear) etc. If it come into the market, who can guarantee, that the WFEs of different sources can be mixed without segregation? General compatibility in such complex systems is practically unsolvable. The problems from phase separation needs no other comment.
Shortly, as I assume only this is sufficient for the FWEs not to be a general market produkt. Not probable you will ever buy them on stats.
Second and more serious problem is the microbiological infection. Water is essential for micro-organizms. Now the'll get it in the form they like nearly the best. CH-water-emulsifiers-additive system is next to unavoidable to be infected sooner or later. The bactericid, fungicid etc.-icid additives are effecive only for a while, these unpleasent bugs will get accustomed to them after some time. Then you have to change them. This is an endless race. Think of the cutting emulsions. These bugs develop disgusting jelly formations, and are prone to make corrosion. If this gets into the feeding system... everyone can imagine the consequences. And an infecion spreads. God save us from it!
Of course this doesn't mean that in very special fields FWEs wouldn't be used under the strickest control. They have got very great advantages eg. the flash point can be lowered to unmeasurable.
In the feeding system the fuel tank is exposed to great changes in temperature. What about icing. Answer is additive. Of course the emulsifier can be a multifunction one, but compexity won't decrease because of dosage.
Some fine filters absorb the water. Consequence swelling and clogging.
Then came the lubrication problems. Introduction of the new extremly low sulphur content diesel fuels has caused a lot. Now a new one would be solved. New additive?
For a while let's have a pause.
As to the other field, cilinder & head.
The water has got beneficial effect on injection, because the in situ developed steam blow up the fuel droplets into very fine particles, better combustion. The steam has got some catalitic effect on burning. The thermodinamic properties of steam are markedly better than CO2, so lowering the relative ammount it in the flue-gas vs. H2O is useful. Conclusion, the caloric efficiency of the engine is higher. Of course this has got its limits. MPG, if FWE is the fuel, another question, because the water is inert, so it lowers the heatig value. The effect on power is similar.
As to the emission problem that might be another matter.
Epigraph: Everythig hangs together. Andras
Let's be a bit more accurate.
There is a significant difference between the fuel-water emulsions in general and the effect of water (or steam) in the engine, specifically on the processes in the cilinder & cilinderhead (burning).
As to WFE generally. Here are two main aspects. Storage and behaviour in the feeding system.
In the storage there are two main difficulties.
The first is stability. Up to my recent knowledge these emulsions has got limited lifetime. The stability of an emulsion depens upon many condition. Temperature and its changes, other materials in the system, mechanical effects (eg. shear) etc. If it come into the market, who can guarantee, that the WFEs of different sources can be mixed without segregation? General compatibility in such complex systems is practically unsolvable. The problems from phase separation needs no other comment.
Shortly, as I assume only this is sufficient for the FWEs not to be a general market produkt. Not probable you will ever buy them on stats.
Second and more serious problem is the microbiological infection. Water is essential for micro-organizms. Now the'll get it in the form they like nearly the best. CH-water-emulsifiers-additive system is next to unavoidable to be infected sooner or later. The bactericid, fungicid etc.-icid additives are effecive only for a while, these unpleasent bugs will get accustomed to them after some time. Then you have to change them. This is an endless race. Think of the cutting emulsions. These bugs develop disgusting jelly formations, and are prone to make corrosion. If this gets into the feeding system... everyone can imagine the consequences. And an infecion spreads. God save us from it!
Of course this doesn't mean that in very special fields FWEs wouldn't be used under the strickest control. They have got very great advantages eg. the flash point can be lowered to unmeasurable.
In the feeding system the fuel tank is exposed to great changes in temperature. What about icing. Answer is additive. Of course the emulsifier can be a multifunction one, but compexity won't decrease because of dosage.
Some fine filters absorb the water. Consequence swelling and clogging.
Then came the lubrication problems. Introduction of the new extremly low sulphur content diesel fuels has caused a lot. Now a new one would be solved. New additive?
For a while let's have a pause.
As to the other field, cilinder & head.
The water has got beneficial effect on injection, because the in situ developed steam blow up the fuel droplets into very fine particles, better combustion. The steam has got some catalitic effect on burning. The thermodinamic properties of steam are markedly better than CO2, so lowering the relative ammount it in the flue-gas vs. H2O is useful. Conclusion, the caloric efficiency of the engine is higher. Of course this has got its limits. MPG, if FWE is the fuel, another question, because the water is inert, so it lowers the heatig value. The effect on power is similar.
As to the emission problem that might be another matter.
Epigraph: Everythig hangs together. Andras
the purpose of water vapor in the combustion process is to limit formation of NOx. It works in a similar way as EGR. Since the water (or EGR) is essentially inert, it does not contribute in the combustion process. But since it is present, it will absorb heat. The end result is lower peak combustion temperatures and less NOx formation, albeit with slightly less power. NOx typically does not form at flame temperatures below about 2800degF.
regards,
Terry
regards,
Terry
Dear Terry:
Sorry, but I cannot aggree with you considering H2O (vapour) to be inert under the condition of combustion, that is well over 1000 degC. In cylinder head the max temp can exceed even 2000 degC! And reaction rate, as a rate of thumb, doubles by 10 degC increase.
To illustrate this think of the blue gas reaction
C + H2O = CO + H2 (elementary school 7. class in our coutry.)
This reaction causes, among others the reduction of PM, mainly soot.
Another example: dry CO doesn't explode in air, only in presence of H2O vapour traces.
The N2 molecule is much stable than H2O, its measurable thermal dissociation begins at about 3000 degC. Nevertheless it is present in the exhaust gases!
The same phenomenon in steam appears at about 1500 degC.
The effect of water on the whole engine cycle is more complex. Let's think eg. of the Cheng cycle. The effect of EGR mainly because of CO2 is definitly detrimental both on the power and on the efficiency.
The absolute amount of NOx in the exhause gas is very little. To invest for decreasing the tiny with ten or so percent is pure deficit. Except when legal limits are at stake.
What's more!!! This NOx mystification is ridiculous in the troposphere. There would be no life if there were no natural NOx production (in the lightnings). The Nitrogen Cycle. Of course in some special case it's a problem, but in general?
On the other hand, from the stratosphere (aircrafts) NOx is able to reach the ozone layer. And it reacts instantly with ozone. Not too much word is about this.
I would be very glad to hear you again,
Regards Andras
Sorry, but I cannot aggree with you considering H2O (vapour) to be inert under the condition of combustion, that is well over 1000 degC. In cylinder head the max temp can exceed even 2000 degC! And reaction rate, as a rate of thumb, doubles by 10 degC increase.
To illustrate this think of the blue gas reaction
C + H2O = CO + H2 (elementary school 7. class in our coutry.)
This reaction causes, among others the reduction of PM, mainly soot.
Another example: dry CO doesn't explode in air, only in presence of H2O vapour traces.
The N2 molecule is much stable than H2O, its measurable thermal dissociation begins at about 3000 degC. Nevertheless it is present in the exhaust gases!
The same phenomenon in steam appears at about 1500 degC.
The effect of water on the whole engine cycle is more complex. Let's think eg. of the Cheng cycle. The effect of EGR mainly because of CO2 is definitly detrimental both on the power and on the efficiency.
The absolute amount of NOx in the exhause gas is very little. To invest for decreasing the tiny with ten or so percent is pure deficit. Except when legal limits are at stake.
What's more!!! This NOx mystification is ridiculous in the troposphere. There would be no life if there were no natural NOx production (in the lightnings). The Nitrogen Cycle. Of course in some special case it's a problem, but in general?
On the other hand, from the stratosphere (aircrafts) NOx is able to reach the ozone layer. And it reacts instantly with ozone. Not too much word is about this.
I would be very glad to hear you again,
Regards Andras
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