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PostPosted: Jan 13, 2014 7:11 pm 
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Such a low boiling liquid does lose the handling advantages that diesel has though (I didn't realise it was so low boiling).


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PostPosted: Jan 13, 2014 8:48 pm 
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DME is as easy or difficult to handle as a propane cylinder. The Chinese make a lot of it from coal and blend it with domestic LPG/propane.
http://www.aboutdme.org/
It is far easier to handle than liquid or compressed methane. Natural gas (methane) could be converted to DME for easier and safer handling in vehicles.


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PostPosted: Jan 14, 2014 1:40 am 
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E Ireland wrote:
Such a low boiling liquid does lose the handling advantages that diesel has though (I didn't realise it was so low boiling).


Yes and no. Tanks need to withstand ~20 bar of pressure so you lose some flexibility in shapes and materials, but on the flipside you can use a sealed fuel system with no need for venting and reduced potential for evaporative emissions.

Of the simple syngas-derived fuels, DME seems best suited for compression ignition (easily ignitable, low heat of vaporization) while methanol looks better for spark ignition (much higher antiknock index, high heat of vaporization to provide some internal cooling). There are some engineering challenges, particularly with respect to high pressure fuel injectors for DME, but the small molecule fuels allow you to avoid Fischer-Tropsch processes and reduce the potential for toxic emissions resulting from incomplete combustion, simplifying exhaust treatment.


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PostPosted: Jan 14, 2014 3:34 am 
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Fischer Tropsch can provide a far wider range of products though which means we will likely have to do it anyway in the future to produce lubricants and so forth (that was its original purpose before it was pressed into service as a fuel substitute process during WWII).

FT is not masively harder than Methanol synthesis and dehydration.
Methanol also has issues in spark ignition engines in that it is hygroscopic which means fuel handling is complicated by the need to prevent it being exposed to moisture/water as it will fairly rapidly dilute itself with the accompanying drop in energy content.

For instance SMDS (an advanced variant of the FT process) can produce gas oil with a cetane number of 76, which is so high as to make DME look terrible (even though it really isn't).
While it might only have a 60% yield for gas oil (25% Kerosene and 15% Tops/Naptha) in the 'Gas Oil' mode of operation it almost doesn't matter as its cetane number is so high as to make it possible to dilute it with inferior mateiral and still put it in the very good range.
If that gas oil is considered too heavy for vehicle use the close control of the catalysts means the product spectrum can be shifted to favour kerosene or any other fraction desired.

Methanol and its derivatives are a blunt instrument that might be 'good enough' but will hinder deployment of alternative fuels because people will dislike the inferior fuel qualities (energy content especially) that they suffer from.


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PostPosted: Jan 14, 2014 4:41 am 
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E Ireland wrote:
Methanol and its derivatives are a blunt instrument that might be 'good enough' but will hinder deployment of alternative fuels because people will dislike the inferior fuel qualities (energy content especially) that they suffer from.


I'm not sure about that. Methanol may have half the energy per liter as gasoline, but if you can make the engine 50% more efficient than current gasoline vehicles, the difference in range is greatly reduced. So you wouldn't need a 120 liter fuel tank to have similar range as a 60 liter gasoline tank, but maybe only 90 liters. I don't think that 30-40 liters bigger fuel tank is a big deal. IIUC a methanol compression engine is potentially more compact than a diesel compression engine so probably you could have zero net volume and weight penalty, but I'd have to check the figures.


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PostPosted: Jan 14, 2014 7:32 am 
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Methanol has a Cetane Number of 5 which basically makes it near worthless for compression ignition engines.
These high efficiency engines (at least those in that presentation you linked) seem to make use of on board reforming to produce a syngas stream AND use a combined cycle system to gain that 25% advantage.

The latter can be applied to a diesel engine and is projected to provide 10-15% fuel economy improvement by itself, and the former seems rather dodgy since it requires some rather fragile catalyst type components in many cases.

Such an engine only has marginal efficiency gains compared to my baseline of a turbosteamer equipped turbodiesel.


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PostPosted: Jan 23, 2014 12:43 pm 
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Sorry, I had ignored this thread and hadn't realized it had gotten so far off topic.

Cold fusion posts pared back. Instigators disciplined.

You can talk about this silly topic all you want. On somebody's else forum.


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