There is a risk to accepting funding and failing to succeed. It can make future contracts more difficult. This is not pure research; it's to improve or apply an existing concept and if the company is unable to make a decent estimate of that it calls into question what else it might have problems with.
No one cares if the task was impossible, they care that someone said they would deliver and failed.
I apologize for "grandstanding." It was the product of my frustration with off-the-cuff dismissal. I believe the technical question you put forward "how much of the combustion chamber's heat energy is lost in the cylinder head? or via the piston?" is answered by the article I linked in response to malbeare. The article at
also sums up the potential benefits that are behind the effort to resurrect the opposed piston architecture:
[ul]
[li]Thermal efficiency: Low ratio of combustion-chamber surface area to cylinder swept volume and elimination of cylinder head mean there's much less heat rejected to the cooling system so more of the heat of combustion goes to propelling the vehicle.[/li]
[li]Lower friction: With no cylinder head bolts to distort the bore, there's less ring friction, and the lower peak operating speed of any compression-ignition engine lowers friction.[/li]
[li]Lower pumping work: Intake and exhaust enter and leave via ports arranged around the cylinder at the top and bottom of the pistons' strokes, so the pistons do no pumping work. With some of these ports open at all times on an engine with three or more cylinders, the supercharger and turbo also operate more efficiently.[/li]
[li]Lighter weight: Lower cylinder pressures mean that even the diesel doesn't need to be "hardened" to the same extent as a conventional four-stroke diesel.[/li]
[li]Cooler operation: Lower peak cylinder pressures and temperatures reduce the amount of NOx and other pollutants produced in the cylinder.[/li]
[li]Horizontal direct injection: Two fuel injectors spray across the cylinder instead of onto the hot pistons, which can cause the quenching that leads to particulate formation. Also, the stroke is long enough to fully burn the hydrocarbons.[/li]
[/ul]
There are a number of challenges to the design that the article doesn't mention.
[ul]
[li]Lack of piston load reversal: Like any two-stroke the rings and bearings suffer unidirectional loads that create problems in lubrication.[/li]
[li]Lubricant in the ports: Like any two-stroke, oil around the rings can pass into the intake and exhaust ports.[/li]
[li]Fuel/Air mixing: Side sprays simply aren't as effective in mixing, particularly given the reduced time available.[/li]
[/ul]
The only explanation that makes any sense to me with regards to the lower heat loss to the combustion chamber of an opposed piston engine is possibly the fact that the two pistons moving away from each other have twice the expansion rate of a single piston moving away from a fixed head *deep breath*.It's kind of like running a crankshaft and rod geometry that promotes a short piston dwell time but without the disadvantages of rapid piston acceleration and high rod angularity.
Just to reply to the challenges, I don't think any of those are truely valid.
Load reverals are tremendously more difficult to deal with. If you look at the architecture of our favorite 2-stroke engines including EMD and Detroit Diesel, the lack of load reversal so simplifies the bearing arrangements that they only have to use half of a bearing. See the blade rod bearing and piston carrier bearing in an EMD and the wrist pin bearing in a cross-head type Detroit Diesel 71 series engine.
Lubricant in the ports doesn't directly equate to particulate in the exhaust. Valved engines have valve guides that do allow oil directly into the exhaust where it can combust poorly. Fully ported engines may actually see an advantage here.
Side injection isn't necessarily a bad thing. Fuel can travel the full diameter of the bore vs only half with a centrally injector prior to being quenched. However, I think an advantage of an opposed piston design is that it allows for a much larger combustion chamber vs. bore diameter due to having essentially twice the stroke without the issues of the connecting rod crashing into the bottom of the cylinder.
The only explanation that makes any sense to me with regards to the lower heat loss to the combustion chamber of an opposed piston engine is possibly the fact that the two pistons moving away from each other have twice the expansion rate of a single piston moving away from a fixed head *deep breath*.It's kind of like running a crankshaft and rod geometry that promotes a short piston dwell time but without the disadvantages of rapid piston acceleration and high rod angularity.
Yes. As far as heat loss and the thermodynamic cycle in general, the OP has all the advantages of a long stroke design while having the mechanical advantages of a short stroke.
