Just because 2 stroke engines were set aside in production vehicles, it doesn’t mean development stopped, in recent years there has been increasing attention paid to these powerful and compact engines and the Grail Engine is an interesting example. It’s a multi fuel, variable compression, highly efficient 2 stroke with built in supercharging and intercooling.
The Grail Engine claims to eliminate cross contamination of fuel and oil, the primary cause one cause of high emissions in 2 stroke engines and why we don’t see them used anymore, otherwise, their high power output would make them ideal as a power unit. Two strokes have always had a higher power to weight ratio and the Grail also claims greater thermal efficiency than current 4 strokes.
A single exhaust valve, 3 spark plugs and a direct fuel injector are located at the top of the cylinder.
Compression takes place within the reed valve air box, pre-compression chamber, vent-to-piston ports, piston-intake-ports & crankcase. As the piston travels upward creating a vacuum beneath the piston, fresh air enters via the intake air box through the one-way reed valve, and fills the external pre-compression chamber, vent-to-piston ports and piston-intake-ports with fresh air.
Compression occurs within the cylinder as the piston travels upward. At Top Dead Center (TDC), direct ignition then single or multiple ignitions occur. This forces the piston down into the cylinder compressing air in the engine crankcase, external pre-compression chamber, vent-to-piston ports and piston intake-ports. Just prior to Bottom Dead Center (BDC), the exhaust valve opens via a standard cam/push rod mechanism or electro-mechanical valve control. Exhaust gases exit via the exhaust valve opening at the top of the cylinder. Compressed fresh air enters the cylinder via piston valve, which forces out the final exhaust. As the piston travels past BDC the exhaust valve and piston valve close and cycle repeats.
The specs state that a 1 liter Grail could have 100 mpg, 180 foot pounds of torque and 200 horsepower, though they don’t specify what sort of vehicle size and weight these mileage figures are claimed for.
As always, another new engine with lots of potential, but until it’s tested and actual output is measured and confirmed, we don’t know how close these numbers are to being true, but wouldn’t it be nice to see powerful and compact 2 strokes returning to production vehicles?
Link: Grail Engine Technologies
john says
http://www.youtube.com/v/4-H03_wGFB0
Are my eyes seeing things that are not there or does this thing actually have a valve in the top of the piston?
BigHank53 says
No, the intake valve is in the piston. Should be able to be fairly light, as it won’t need a long stem and powerful spring attached.
Paul Crowe - "The Kneeslider" says
Well, actually, look again. I included another image at the end of the post. Just click to enlarge.
BigHank53 says
Oops. I thought it would have been opened by gas pressure alone.
FREEMAN says
I’ll believe the numbers when they’re not theoretical. Aside from that, it’s a cool design. Hopefully, it actually get’s built and run.
Paul Crowe - "The Kneeslider" says
If I understand the operation of this engine correctly, everything necessary to run gasses into and out of the engine is performed by the engine itself, you don’t need tuned expansion chambers that result in the narrow 2 stroke power band. The pressure in the pre-compression chamber can be adjusted on the fly and gives efficient operation over a wide rpm range. It’s a 2 stroke with a wide power band like a 4 stroke, while retaining the power on every stroke advantage and lower parts count of a normal 2 stroke. Pretty cool.
john says
It would be more interesting as a compression ignition engine.
GenWaylaid says
I concur. Direct injection and compressed-air scavenging are good ways to get around the common two-stroke emissions problems. Aprilia has been using similar methods in their DiTech two-strokes for at least ten years now.
The use of poppet valves for both the exhaust and the scavenging air means that valve timing is well controlled with no need for a tuned exhaust. With no ports in the wetted portion of the cylinder wall, one cause of oil consumption has been removed, too. Scavenging looks to be very thorough, since the air flow would be from one end of the cylinder to the other.
Unfortunately, the choice to scavenge with compressed crankcase air means that this engine will still consume oil (in the form of fine, suspended droplets) like any two stroke with case induction. I’m also not convinced that the gases in the cylinder will be sufficiently expanded at BDC that the crankcase pressure is higher. I suppose if the scavenging goes backwards you can always call it EGR.
BoxerFanatic says
Interesting.
Would make a nice small engine, stationary power unit, or even an electric generator.
Mark says
When I saw the head line I thought the story was going to be about the Holy Grail of engines. Count me as surprised to see the engines name is Grail. Nice review. Lets see where it goes. Thanks.
sandrews46 says
I don’t think that the issue with emissions is a cross contamination issue, that can be addressed with sealed bearings and direct injection, I think the issue is poor scavenging/efficiency at part throttle, and maybe this solves a lot of that problem.
Kevin says
Interesting design idea, I am not sure if i see benefits of a piston valve and external compression chamber. Those sound like extra weight for me. Maybe they add to emissions and fuel economy for future car regulations and may eventually be necessary. But from a motorcycling, light weight, low complexity standpoint, a “basic” DI 2-stroke would probably be better.
I would agree that the expansion chamber is unnecessary because there is a controlled exhaust valve that can be closed after scavenging is complete, but before loss of fresh air. There was a design by Boyesen that did that, but never got used.
I want to address teh emissions though. The main problem is not the contamination of oil in the fuel. The problem is unburnt fuel escaping into the exhaust. DI fixes that and gets rid of the oil in the fuel. This design adds some additional control to porting.
Bryan S. says
interesting… does the stil still go in the fuel?
Bryan S. says
that is, does the oil still go in the fuel? Im trying to see how this thing would be lubricated….
discontinuuity says
Interesting, but I don’t see a lot of new technology here. I’m not sure why you would want to vary the primary compression ratio (I think that’s what the weird intake thing is for), since with two-stroke engines you usually want to have as high a ratio as possible (ie, very low crankcase volume).
The two extra displacer pistons on the sides of the main piston are interesting, but I’ve seen that before (on a French racing bike, IIRC). The exhaust valve thing has been done on marine two-stroke diesel engines for decades. And I don’t really understand the benefit of the in-piston valve over regular transfer ports. It seems like there would be lots of valve flutter at high rpm.
john says
I didn’t even think about the valve in the piston coming open at high RPMs. yeah, when it hits top dead center on the compression stroke inertia will pull that valve open easily if there isn’t some kind of a lock on it. I don’t even think the RPMs need to be all that high.
discontinuuity says
It would theoretically be kept closed by the compressed gasses in the combustion chamber, but at high rpm the inertia would overcome this. It would make more sense to use a spring to hold it closed and have the bottom of the valvestem run into something at BDC to open it.
GenWaylaid says
Good point. I just assumed that was what was going on.
B50 Jim says
Lots of applying old ideas in a new package to address the main shortcomings of 4- and 2-stroke engines. But the valves add complexity and weight, and I’m not sure there would be enough advantage to make it significantly better than a well-sorted 4-stroke. I’m especially skeptical of anyone who claims 100mpg for a 1-liter engine. Maybe in a Smart car tuned for max mileage but totally impractical, but on actual roads under driving conditions, it would be considerably less.
Still, it’s great to see someone doing things to improve on the IC engine. The 3-D prints are first-rate, and I’ll be interested to see if it gets built.
Richard says
I don’t see much novelty here, it’s a uniflow. There were people doing this more than 100 years ago. Crankcase compression isn’t new, injected petrol two-strokes were flying on airplanes in the 60’s, and in piston valves were used in WWI Gnome Rotary engines in 1914. Harry Ricardo did it all, and more, in 1942.
Wave says
Yep, I was going to mention the Gnome engine. As far as I know, the main reason they did it was to simplify the valvegear arrangements for a rotary engine, and also potentially allow some supercharging effect from the centrifugal force of the air-fuel mixture flowing radially outwards from the centre of the crankcase to the piston tops.
Paul Crowe - "The Kneeslider" says
The Grail folks acknowledge the Gnome engine and many other sources for ideas used in the Grail. If you scroll to the bottom of their tech page, you’ll see a list of links, the Gnome is among them.
Zippy says
“Yes I know where you can find the most holy grail…but come only if you be men or valor…for death awaits with huge pointy teeth”
Tim the Enchanter
Tomi says
Somewhat similar, z-engine:
http://www.aumet.fi/
mARK says
This reminds me a tad bit of the f.a.s.t. engine that Tim Hickox proposed. I believe it was made some time ago at a rather high weight, but people are working on redesigning it to be nice and light.
Carolynne says
Happy Fathers Day to all you Dads! I know I am totally off topic but I wanted to wish you all a great day and I am sure your kids are all thankful to have the cool Dads that can fix thier stuff for them.
Paulinator says
Hey Thanks!!!
Paulinator says
Maybe I can’t follow the premise that this engine is modelled around, but it seems to ignor compressibility, the mechanical inefficiency of reed valves and the limited swept volume of the of the piston relative to the crank case. I’m a skeptic until I see it run.
Ednilson says
Eu achei fantástico.
Isse projeto como um tetracilindrico em motos seria superior a qualquer outro motor de 4 tempos …
Uma pena que nenhuma das poderosas assuma isso, todas tem medo. Acham melhor ficar com certo que tentar o duvidoso…
Quem poderia produzir esse motor ?
Angsengl says
Interesting design but where is the prototype?