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DME is kind of between LNG and diesel. The fuel is much easier to transfer and store than Cryogenic LNG. Its very similar to propane as a liquid at room temperature but pressure slightly above atmospheric. It is a compression ignition fuel so it can operate at diesel like efficiency because it doesn't have lower compression and Knock issues like natural gas. Its oxygenated leading to the lower PM emissions, but will still have some knock issues due to mixing controlled combustion. The very low viscosity make the direct injection system a bit of a challenge, but because its oxygenated, it doesn't need the very high pressures that diesel does for low PM emissions, likely 4,000psi instead of 35,000psi. But the infrastructure challenge will likely limit it to niche markets at first. One thing I'm betting is that it won't become a locomotive or marine fuel because like propane is is heavier than air when it leaks so safety is an issue that is hard to overcome at the larger onboard volume in those applications.
Here is some information on a very simple way to hybridize commuter trains in the US that will cost 1/5 or less the cost of conventional catenary electrification. Additionally it allows converting the infrastructure over one train and one station at a time. It also eliminated the issue of having to change trains when you get to the end of the catenary wire.
If you save 30% in fuel, that makes up for the heavier engine/genset. Direct drive the rotor and get rid of the transmission, even more weight saved and safer too. Rotor speeds were quoted backwards, you want slower rotor speeds for high speed forward flight, the tip speed of the advancing rotor blade is a major part of a helicopter speed limitation. With a tilting motor/mast and rotor system, they may be able to get rid of the articulation. No gear box needed for the tail rotor, just a good motor and fly by wire, maybe double windings and inverter boxes for redundancy, helicopters can land without a tailrotor as long as they have forward speed. When I first read the title I thought this was another dumb idea, but with all the flapping bits and gear train on a normal helicopter that are critical to flight safety, a tilting electric motor with a battery backup sounds like it could work...
What kind of thermal efficiency are they getting on the PW's and the FJ33's? (is there a convenient TSFC to BSFC comparison??) I see that Capstone is getting 32.5% at peak power in a very simple recuperated turbine, but that is far below current diesel gensets at 42%.
I've seen this at a few SAE shows, its looks impressively simple, but I imagine it has an Achilles heel somewhere similar to why the Wankel engine hasn't caught on except in specific applications. It was meant to be a diesel engine and my personal hunch is that there is a fundamental issue with injecting fuel from the side of the chamber in between the pistons, instead of straight down as in conventional modern diesels.
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Mar 14, 2010