Take a look at this link

http://www.sciencedaily.com/releases...0723175256.htm

The article makes it sound like HCCI is new. This has been studied for probably 10 years now. I know I have documents pulled from the web on the topic from 2000 or so.

I didn't have time to read the whole article.... diesels have always been the most themaly efficient internal combustion engines and still are. It is amazing how much research and money goes into spark ignition engines ( or variants ) that have no hope of matching the efficiency of diesels.... There is a reason there are no more spark ignition over the road trucks, trains, ships etc...... Also that diesels always win the highest MPG contests.

The article shows a diesel (kind of) interest revival, which in fact is the way to go if we are to make the best of the available resources to us.
The direct injection method still is the best known to mankind, and no premix or lean-burn technique will match it yet.
The ship's diesel I worked with in the early sixties, tested, and measured in the shipyard and aboard had an efficiency of 48%. The propeller shaft had torsion measurements for torque, and we had very precise rev counters and stopwatches. Every single revolution was counted in the time span we did our calculations of fuel consumption, rpm and torque. In addition, we took cylinder pressure diagrams of each cylinder, and compared it all to the supplied fuel data. (calorific values) to get the energy balance as accurate as possible.
These engines, running at about 100 rpm, had a lot of piston power, in the range of 1000 hp each, used uniflow scavenging (ports and valves) and turbo-charging, so exhaust gas energy was not wasted.
The heat still remaining in the exhaust gas after driving the turbos was further utilized for generating heating steam and evaporating water (for drinking and bath)

I believe to this day, no car engine yet reached that kind of efficiency, though they are homing in.

Pe, for your reference:

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

HCCI combustion is essentially a premixed, rather than injected, compression ignition engine. Just like our glow and model diesels. In model we just richen up portions of the throttle range to make things work. This is not acceptable for vehicles where emissions are a concern. The other main problem in HCCI engine is predicting the ignition timing.

The GE system looks impressive at 60% and specific fuel consumption of 123 gr/kwh, though I have no confidence in the KW measurements of a turbine engine. It must be derived from thrust and drag force vs speed. I am inclined to see the 60% efficiency as wishfull thinking, though I know immense progress has been made in the field of airplane turbines. If they are even close, that is very impressive for a non-stationary powerplant.
So far, all the better performers are very large diesel engines especialy ships diesels. The 48% I mentioned was a two stroke in the sixties, not too large, and without heat recycling, like the Modern engines.
My memory fades a bit, but if I recall correctly, specific fuel consumption was about 168 grams/kwh or something like that.

This is an interesting discussion, brought up in Greg's Wiki link....

But let's take a realistic look at the issue:

The common Thrush crop-duster/sprayer, with all its variants, is originally equipped with a Pratt & Whitney, or a Wright radial engine, producing 550-600, or 800 HP and weighing 392, or 465 kg net...

These engines have a typical gas piston engine ~0.45 lb/HP/h SFC.
Virtually all these radials have been replaced by Pratt & Whitney PT6A (most), or Garrett Airesearch TPE331 turboprops.

These turboprops feature a 30% higher SFC than the original piston engines (0.595 for the 750 SHP -34B), but a weight of only 143 kg net.

This allowed the plane over 500 kg more payload, which the weight of the extra fuel needed is only a small part of...
And as to fuel, nearly any combustible fluid can be utilized...

With a turbine it could take more liquid/powder and spray/dust more area per flight, fly faster even with the added payload, due to having more power and a streamlined nose...

Re-engining to a turbine is preferred to overhauling, despite the humongous initial cost... which eventually saves the operator a lot of money.


The ultra-efficient 1949 Napier Nomad aero engine (has not been equalled yet) did not make it very far, because it was very heavy...


A model Diesel uses about 35% less fuel than a model glow engine (and give a bit more power) and weighs an ounce more on average.
This is what is taken into account.

Dar, those are interesting points. It all depends what business you're in. A 60 MPG Honda Insight isn't a good choice for a cargo carrier like UPS even though it is economical. Just as much as a 10MPG Freightliner cargo hauler isn't a good choice for hauling groceries even though there is plenty of room inside.

I like this wiki page:

http://en.wikipedia.org/wiki/Fuel_ef...transportation

In particular the 653MPG they claim for a a human on a bicycle.

That brings up an another thought. I recently saw a crop duster in our area spraying fields. it wasn't what I expected because it was a helicopter. I don't know how the books work out on that but maintaining a heli isn't exactly cheap. My first thought was how does he make money?