Diesel Power and Diesel World's water/met articles this month (confused)

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Speardog

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I was under the impression that water/meth advanced timing on a diesel (as opposed to retarding it like on a pump gas car). According to one of these magazines recent articles (can't remember which one), it retards compression ignition. So is water/meth to blame for burnt up motors??? There is too much conflicting info on the subject.

Does anyone on this board actually been apart of research of water/meth. I have been wanting to hook it up to my truck, but everyone has me scared of it on the forums. Someone shed some light

Jeff
 
Speardog said:
I was under the impression that water/meth advanced timing on a diesel (as opposed to retarding it like on a pump gas car).
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No. Fuel injection is solely responsible for base ignition timing, its what ignites the methanol in the mixture.

According to one of these magazines recent articles (can't remember which one), it retards compression ignition.
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No, it advances ignition in that the fuel burns faster. Base timing stays the same. Methanol burns much faster than diesel which means a faster flame front and pressure rise with less delay igniting the rest of the injected diesel.

So is water/meth to blame for burnt up motors?
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No. Bad drivers who ignore signs of problems are completely to blame for melted engines. Those kind of people ignore obvious symptoms like black smoke when cruising or at idle, reduced power, high EGTs, pinging (detonation from too much methanol for a topic-related example) or drivers that think black smoke is "cool".

Does anyone on this board actually been apart of research of water/meth. I have been wanting to hook it up to my truck, but everyone has me scared of it on the forums.
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Don't let internet trolls scare you away. W/M injection works great with diesel engines as long as you understand how much to inject with the water:methanol ratio you're using. Its far far safer than using nitrous, propane or CNG.
 
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Actually, the eponymous compression-ignition engine uses the heat of compression to ignite any fuel present in the cylinder... and methanol injection via wet-flow increases effective timing (i.e. better pull a few degrees for 50% load) ;)
 
That's what I'm wondering. I use the Diablo trinity with extreme power puck right now, which gives me little to no adjustability. Don't know if i can run the extreme rkl tune with power puck turned up AND 49/51 meth/water.
 
300D said:
No. Fuel injection is solely responsible for base ignition timing, its what ignites the methanol in the mixture.


No, it advances ignition in that the fuel burns faster. Base timing stays the same. Methanol burns much faster than diesel which means a faster flame front and pressure rise with less delay igniting the rest of the injected diesel.


No. Bad drivers who ignore signs of problems are completely to blame for melted engines. Those kind of people ignore obvious symptoms like black smoke when cruising or at idle, reduced power, high EGTs, pinging (detonation from too much methanol for a topic-related example) or drivers that think black smoke is "cool".


Don't let internet trolls scare you away. W/M injection works great with diesel engines as long as you understand how much to inject with the water:methanol ratio you're using. Its far far safer than using nitrous, propane or CNG.
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It burns faster than diesel, but it also ignites later than diesel, if I'm not mistaken, since it has a 470 C ignition temp. So does it really affect timing at all then?
 
Sure - auto ignition is >800*F at atmospheric... but those aren't intra-cylinder conditions. ;)

Several environmental factors can change a chemical's AIT - a CI engine has at least 4 that serve to reduce methanol's.
 
so what is the in cylinder condition when water/meth goes into the cylinder? Just trying to understand
 
One of them - possibly the largest influential factor - is >1bar, which reduces AIT.
 
Sure - auto ignition is >800*F at atmospheric... but those aren't intra-cylinder conditions.

Several environmental factors can change a chemical's AIT - a CI engine has at least 4 that serve to reduce methanol's.
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Hey Mike!!!

Can you expound on this? I always enjoy your posts, and am not doubting what you say here; rather, I'm just trying to make sense of everything.

Here's a quick background on what's got me thinking:

There has been recent work in light duty diesel engines running in an RCCI combustion mode (reactivity controlled compression ignition), where gasoline is injected in the intake manifold via PFI injectors, and the diesel is injected normally via DI injectors on the engine. At moderate loads, significant amounts of gasoline are injected (~60 - 80% of total fueling) into the intake plenum, and then the DI diesel event phased accordingly for proper combustion.

Surprisingly (to me at least), the introduction of semi-premixed gasoline serves to retard injection timing, very similar to how heavy EGR delays ignition. For example, when running 60% gasoline, injection timing of the DI diesel event is ~37° btdc. When running 80% gasoline, DI timing is ~ 60° btdc.

When combustion occurs in this RCCI mode, it happens very quickly...i.e., there is no "tail" on heat release as things continue to burn. It lights off and burns rapidly. The efficiency benefit comes from being able to center combustion phasing (CA50 point, or 50% mass fraction burned) immediately after TDC, and having all effective work due to combustion done within 20 - 30° atdc!

Gasoline generally is thought to have an AIT of ~ 250 - 260° C, whereas methanol's AIT is much higher, at around 450 - 470° C. I know that people say running methanol injection on our trucks advances timing, but I haven't reconciled this with the data from the RCCI combustion that I know is true.

Additionally, "In general, aromatics and alcohols have low cetane numbers (that's why people using methanol in diesels convert it to dimethyl ether). One of the obvious effects of running on low cetane number fuel is the increase in engine noise." Low cetane tends toward longer ignition delay, and agrees with the RCCI data. But methanol?

Interested in hearing your thoughts...


--Eric
 
Good question Eric - since cetane is essentially a fuel's quantifier of ignition delay, while octane is a measurement of a fuel's propensity to combust at a controlled rate - blending fuels the different fractions of which are typically expressed in only one or the other test method's equivalent can make understanding their combined effects on the combustion event more difficult.
Octane & cetane are related, though only indirectly - not a simple (or linear, for that matter) reciprocal - but using them independently can assist modeling the BOOM.
For example, gasoline & diesel AITs are similiar - as are their energy densities, but run #2 through an SI engine to grenade it & put unleaded in your CI mill so it just sounds like it's exploding...
but you can respectively view fuels' octane & cetane ratings either as a propensity to knock, or rather as an arbitrary ignition delay value.

In the case of RCCI, intake valve closing & EGR percentages are a major factor in it's usefulness, so it isn't really analogous to methanol PFI; additionally, gasolines' function in RCCI is as much catalyst as fuel, so there's a marked difference in regard to methanol's significantly lower volatility - especially in regard to the many & varied fractions present in pump gasoline.

Even though the approximate average of methanol's research & motor octane numbers seem to indicate that it would simulate iso-octane's effect on combustion event timing & stability (delaying ignition & increasing knock resistance, respectively), methanol's relatively high AIT compared to diesel is more than offset by it's much lower ignition point (delta in excess of 150*F occupies a significantly different position on the crank angle/heat of compression curve) - particularly when AIT-reduction environmental factors are considered.
It's helpful to remember that both gasoline and methanol are flammable, while diesel is combustible.

As far as combustion noise, confusion should be avoided between a sharp spike of cylinder pressure due to combustion rate and the collision of discretely propagating wave fronts of combustion.

Also, RCCI extracts all effective work from combustion by 30*ATC?
Doesn't seem very efficient with maximum mechanical advantage ~90*ATC, and best expansion rate not nearly so close to TDC (at least not with diesel fuel).
 
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These are all nice theories, but it really doesn't tell me how much water/meth at a certain % and volume is safe at different degrees of timing. Also AIT of meth is skewed by the fact that it is a polar solvent with water which naturally extinguishes combustion.
 
300D said:
How can it alter timing when the diesel is injected at a fixed time?
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I think the theory is that because the water meth enters the combustion chamber prior to compressed ignition, there is technically a fuel/air mixture similar to a internal combustion (gasoline type) engine. I would think because meth is a polar solvent with water, that it would delay the ignition of itself after the injection event. i don't know all the specs about it. such as: does the water evaporate too quickly to delay ignition of the meth at time of compressed ignition at a 50/50 mix at a certain pressure and volume of water/meth injection. That is what I am after
 
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