Would a diesel-electric hybrid be better mpg than gas-electric hybrid

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  • #26
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Smaller but not lighter weight that I can see. That high compression comes with a weight cost, and thus a $ cost. Observe that we do not see diesel back pack leaf blowers, or diesel push lawn mowers.
technically the glow plug RC engine is a 2 cycle diesel, and it is the lightest/hp IC engine available.
cheap to manufacture, robust. with some minor "improvements" it would probably run a leave blower cleaner than a conventional 2 cycle. not specifically cleaner, but still a tiny diesel in a lightwieght package

dr
 
  • #27
mheslep
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technically the glow plug RC engine is a 2 cycle diesel, and it is the lightest/hp IC engine available.
cheap to manufacture, robust. with some minor "improvements" it would probably run a leave blower cleaner than a conventional 2 cycle. not specifically cleaner, but still a tiny diesel in a lightwieght package

dr
Existing example?
 
  • #28
Mech_Engineer
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He's correct that most R/C engines are compression ignition, which technically makes them a 2-stroke diesel cycle engine (although they use a nitro-methanol mix for fuel rather than diesel fuel). They also have excellent power-per-weight and power-per-displacement ratings due to their very high operating speeds (30,000+ rpms) (although they don't run very cleanly, and I wouldn't call them reliable).

One example would be this engine (considered a big block in the R/C world): http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXLGH6&P=0". It's a nitro engine (meaning it runs on a mix of methanol and nitromethane, and is compresison ignition with a glow plug), 0.298in^3 displacement (5.0cc), 36,000rpm redline.

Displacement: 0.298 cu in (5.0cc)
Bore: 0.728" (18.5mm)
Stroke: 0.717" (18.2mm)
Practical RPM: 4,000-36,000
Power Output: 3.0 ps/28,000 RPM
Weight: 12.7oz (360g)

This results in 600hp/l, and 8.33 hp/kg. I would not be surprised if engines in this market are higher output pound for pound than any other naturally aspirated engine (other than possibly Formula 1 and turbine engines). It's basically all about engine speed.
 
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  • #29
mheslep
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He's correct that most R/C engines are compression ignition, which technically makes them a 2-stroke diesel cycle engine (although they use a nitro-methanol mix for fuel rather than diesel fuel). They also have excellent power-per-weight and power-per-displacement ratings due to their very high operating speeds (30,000+ rpms) (although they don't run very cleanly, and I wouldn't call them reliable).

One example would be this engine (considered a big block in the R/C world): http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXLGH6&P=0". It's a nitro engine (meaning it runs on a mix of methanol and nitromethane, and is compresison ignition with a glow plug), 0.298in^3 displacement (5.0cc), 36,000rpm redline.

Displacement: 0.298 cu in (5.0cc)
Bore: 0.728" (18.5mm)
Stroke: 0.717" (18.2mm)
Practical RPM: 4,000-36,000
Power Output: 3.0 ps/28,000 RPM
Weight: 12.7oz (360g)

This results in 600hp/l, and 8.33 hp/kg. I would not be surprised if engines in this market are higher output pound for pound than any other naturally aspirated engine (other than possibly Formula 1 and turbine engines). It's basically all about engine speed.
Then I wonder why we don't they see inroads for lawn mowers and leaf blowers?

I can't find any compression figures at the link. It's the high compression that typically drives up diesel engine block weight. Maybe that's the answer here: nobody cares if the occasional R/C engine destroys itself.
 
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  • #30
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He's correct that most R/C engines are compression ignition,
No he isn't. Model engines are not compression ignition engines and rely on a glow plug for ignition. Ignition of the methanol vapor occurs because it reacts with platinum (or a similar catalyst) in the glow plug coil causing it to ignite. It is not ignited by compression, although greater pressure does aid in the rate of the reaction.

http://en.wikipedia.org/wiki/Model_engine

There are also "diesel" type model engines but they work on similar principles as methanol power engines and don't really have much in common with true or full scale diesel engines.

You are right about the power density though. I run a http://www.osengines.com/engines/osmg1951.html" [Broken] in my rc heli and am always amazed by the amount of power produced in such a little package, especially when running 30% nitro.
 
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  • #31
Mech_Engineer
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No he isn't. Model engines are not compression ignition engines and rely on a glow plug for ignition. Ignition of the methanol vapor occurs because it reacts with platinum (or a similar catalyst) in the glow plug coil causing it to ignite. It is not ignited by compression, although greater pressure does aid in the rate of the reaction.
Learn something new every day!
 
  • #33
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Anyone know what the delay is on these?
http://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition

GM just announced a prototype of one and said it may be in production in 10years.
One of my professors works on this stuff at GM told me that the biggest problem is control. In short, HCCI is just a very very complicated task to accomplish due to the complexity of controlling valves, timing, ignition, fuel injection ,etc. To use it for anything beyond light loads is an extremely difficult task to accomplish.
 
  • #34
mheslep
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One of my professors works on this stuff at GM told me that the biggest problem is control. In short, HCCI is just a very very complicated task to accomplish due to the complexity of controlling valves, timing, ignition, fuel injection ,etc. To use it for anything beyond light loads is an extremely difficult task to accomplish.
Interesting. Those are the kinds of problems that pay off big when a solution is found: complex control solution that raises the bar, but minimal materials for construction in production.
 
  • #35
mgb_phys
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One of my professors works on this stuff at GM told me that the biggest problem is control. ... complexity of controlling valves, timing, ignition, fuel injection ,etc.
A modern engine is already a pretty complex system, I don't see this adds much.
I can see that GM probably doesn't want to launch a diesel in the US but Merc and VW had prototypes 3-4 years ago.
Interestingly Merc see it as a way of upping the MPG and reducing the CO2 of their big sedans so they don't get slammed by higher taxes in europe. So it might be that you don't want to do too much too soon since the regulatory limits will just chase you down.

VW are very happy selling small turbo diesels (more than 50% of new small cars in europe are oil burners - and a big chunk of them are VW) they see the future of this technology that it can burn pretty much anything without modification. That obviously saves them tooling between different markets but I don't think individual consumers are going to switch between ethanol, biodeisel, vegatable oil at the pumps from day-day.
 
  • #36
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A modern engine is already a pretty complex system, I don't see this adds much.
You can't even compare the complexity of a regular modern engine to that of an HCCI engine the complexity is so great. With modern engines you really only need to control spark timing, fuel flow, and throttle, along with some ancillary devices like cooling. With HCCI, you need to control EVERYTHING. Its not like a regular engine where you have fixed valve timing. The valves need to be controlled independently and with a very high degree of accuracy which means high speed/pressure hydraulics instead of cam shafts. Temperature sensors and pressure transducers are required all over the place and not to mention the computer hardware to run all this.
 
  • #37
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A modern engine is already a pretty complex system, I don't see this adds much.
I can see that GM probably doesn't want to launch a diesel in the US but Merc and VW had prototypes 3-4 years ago.
Interestingly Merc see it as a way of upping the MPG and reducing the CO2 of their big sedans so they don't get slammed by higher taxes in europe. So it might be that you don't want to do too much too soon since the regulatory limits will just chase you down.

VW are very happy selling small turbo diesels (more than 50% of new small cars in europe are oil burners - and a big chunk of them are VW) they see the future of this technology that it can burn pretty much anything without modification. That obviously saves them tooling between different markets but I don't think individual consumers are going to switch between ethanol, biodeisel, vegatable oil at the pumps from day-day.
HCCI isn't a diesel per se (although I think you may be able to use diesel in them). And the control system for HCCI isn't even in the same league as any current engine.

HCCI is putting requirements for control on things that currently we can't. E.g. Exact cylinder temperature on a cycle by cycle basis. The bold bit is what makes this such a task.

It can (and will) be done, it just needs two things time and money.
 
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