You are okay with scratch designing a 3 or 5 cyl rotary engine (from available bits), working out the details of an electric blower from stock bits (that would need logic circuits to keep i sync'ed with engine demand), scratch designing a PSRU...but an EFI system is right out of the question because it is too complex? That would seem, to me, to be among the simpler things (design and operationally) of the whole undertaking.
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Kiwi303
Well-Known Member
Easiest approach I can think of for spark ignition diesel is the old Diesel+Propane trick in reverse. It just means double the fuel system.
In the classic system the compression ignites the diesel, which lights the propane which carries the flame through the chamber more efficiently allowing better consumption of the diesel droplets (diesel atomises into droplets, propane is gaseous vapour) ensuring better utilisation of the fuel and less unused hydrocarbons going out the tailpipe.
in a spark ignition diesel, the spark would light the propane, which would light the diesel...
what was a workaround to improve power and efficiency in 70's and 80's diesels could be a useful system for a 2020's engine, and with the low propane consumption, possibly even just utilize those single-use small camping stove cannisters.
In the classic system the compression ignites the diesel, which lights the propane which carries the flame through the chamber more efficiently allowing better consumption of the diesel droplets (diesel atomises into droplets, propane is gaseous vapour) ensuring better utilisation of the fuel and less unused hydrocarbons going out the tailpipe.
in a spark ignition diesel, the spark would light the propane, which would light the diesel...
what was a workaround to improve power and efficiency in 70's and 80's diesels could be a useful system for a 2020's engine, and with the low propane consumption, possibly even just utilize those single-use small camping stove cannisters.
Pretty cool. Does the lowered CR (since no need for compression ignition) reduce the required mass of the metal bits, putting things closer to a gasoline engine than a typical diesel (for the equivalent HP)? How about the expected torque/RPMs? It would be nice to run slow with high torque to improve prop efficiency.
As a bonus, I'd think there'd be an overall improvement in crash safety compared to gasoline. The higher flashpoint diesel is a huge plus, and the small propane tank is strong and easily made stronger. "Shut off on open line" valves are available. Inverted flight would require some adaptations when using LPG.
PMD
Well-Known Member
Wasn't thinking of electric blower, but more like a 20VDC brushless drill motor connected directly to blower shaft being used as both starter and generator. The tech actually exists at TURBO speeds, but would be adapted from hardware store bits for 4 or 5 x crank speeds (meaning a fairly large diameter compressor wheel but a custom housing to allow full perimeter feed as each cylinder in rotation demands). Big truck and marine turbos have enough impeller to do that, but shaft ends inside instead of passing through.
Personally, I understand the need for electronics, but in a backyard level of build it screams for simplicity of all mech tech.
PMD
Well-Known Member
Yes, sort of scaled up Ross with a blower (not shure how these were charged and scavenged nor started, but the one bottom left wheel is interesting.
Spark ign diesel does NOT need a WMD profane bomb to ride along. It is already in use in some multi-fuel designs for military purposes. Going 2 cycle and diesel is of course my personal preference, but I can't think of any 2 cycle chain saws that are diesel powered.
I should mention: with modern HPCR you can shape MEP curve of cylinder pressures so as not to need much/any more mass of material vs. gasoline to contain same. Definitely NOT mech tech but requiring the very latest and best of electronic engine management and hardware to pull it off.
Not so sure about the 'very', but for a small high rpm gear reduced 2 stroke engine multiple injections are likely to be limited with current piezo injectors and cpu speed......I haven't' done any math.
Did a search for diesel chain saw.
Jonsereds XA back in 1954 to 1060 is the only one I could find. Not exactly user friendly.
PMD
Well-Known Member
Piezzo injectors promised more than they seemed to be able to deliver, but current solenoid-type HPCRs can manage as many as 9 cycles at something like 3,000 RPM. Varying the pulse width is of course how "rate shaping" is accomplished (moving the peak of cylinder pressure curve into an area where it is more advantageous re: rod and crank angle.
I wonder if there was a Tim Taylor episode featuring a 5.9 Cummins powered chain saw??
Rasmus Wiig in Norway, late 1940's, tried like heck to get people to buy into diesel saws. His Comet was actually lighter weight than most gas saws at the time. With fuel injection instead of a carb, it could run, as he often demonstrated, after being dunked completely under in a barrel of water. The saw used a tandor heated with propane stored in the handles and lit when the operator wanted to start the saw. Once started, the tandor continued to glow from the heat of combustion, and the propane was turned off.
Initially Wiig produced them himself in his "Norwegian Saw Blade Factory", later licensed them to Como as well.
Cold weather = lower pressure propane in the small handlebar reservoirs, so they were hard to start when temperatures dropped.
Wiig & Como combined may have sold almost a couple thousand saws, but they threw in the towel in 1954. They designed a new model and contracted the textile company Jonsreds to manufacture them. That's how Jonsreds got into the saw business.
Jonsereds eventually bought the designers out. Jonsreds then struggled along with several differen models of diesel saws including a few hundred for export with glow plugs, until 1957, when they too gave up on diesel & brought out their first gas saw.
With the right contacts in Scandanavia, there may still be enough parts saws in sheds and such for a few engines as you envision. All the saws (engines) seemed to work well & reliably. Just not convenient to start, and the marketing juggernauts of established gasoline saws over ran them, essentially.
smt
Edited: "Alternate option" - Buy the plans and kit from Metal Lathe Accessories, and scale it up.
These run beautifully. I never made one, but the designer demonstrated one on the table in his kitchen for me, once.
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This post got me curious again, i've been trying to stay away from antique saws 'cause there's too much to do on my airplane.
It looks like someone put a Comet up on youtube.
They have to have run cleaner than this one, Rasmus Wiig seems to have been a pretty serious designer & really thought diesels would be better. But if this is an examply, your airplane would not need a smoke system.
The early saws were 3in ^3/ 48.5 cc
Can't find much on the later versions, but there is a lot on the web about them.
Also seems to be a fair amount of scuttlebutt/"iffy" info & opinions on the saw forums
& of course as i trip through the cellar over parts of my 250cc Disston twins, the idea of a flat 4/500 does come to mind.
No, seriously, there are better modern engines to start with.
smt
It looks like someone put a Comet up on youtube.
They have to have run cleaner than this one, Rasmus Wiig seems to have been a pretty serious designer & really thought diesels would be better. But if this is an examply, your airplane would not need a smoke system.
The early saws were 3in ^3/ 48.5 cc
Can't find much on the later versions, but there is a lot on the web about them.
Also seems to be a fair amount of scuttlebutt/"iffy" info & opinions on the saw forums
& of course as i trip through the cellar over parts of my 250cc Disston twins, the idea of a flat 4/500 does come to mind.
No, seriously, there are better modern engines to start with.
smt
Highplains
Well-Known Member
I am curious why you only mention an odd number of cylinders for a two stroke engines?
Kiwi303
Well-Known Member
I don't know about that, when i was dealing with that it was the early 2000's and was just an electrical solenoid downstream of a regulator rigged to a relay on the alternator output. If volts = 0 relay closed, if volts >0 relay open. Open relay = solenoid open and propane flowing into the manifold. So if the alternator was turning (engine running) the propane was flowing at a single set rate into the engine.
It was a workaround for resetting old mechanical injection diesel pump engines with bad smoking under heavy throttle. The better combustion cleaned up the tailpipe, and there was a small but noticeable boost in power. Weight etc wasn't a consideration, CR was still the same.
PMD
Well-Known Member
Not sure who you are asking, but in my case, 3 is the magic number for 2 cycles and 5 for 4 cycles. These are engines with overlapping power pulses that don't have torque reversals (in the case of 2 cycle triples, they actually do, but very small) to "ring" the propeller - making for a lighter prop and PSRU.
Anecdote on spark ignition diesel:
A number of years ago I lived more off the grid. Loaned my Mom and her late husband a small Honda generator, a 650 watt unit if I recall. Came and got me one day because it would not start. Well, we often had to refuel these little things in the dark, halfway through a movie or something, and Doug filled it with #1 diesel instead of gas. Kept right on running while hot, just wouldn't start when cold.
A number of years ago I lived more off the grid. Loaned my Mom and her late husband a small Honda generator, a 650 watt unit if I recall. Came and got me one day because it would not start. Well, we often had to refuel these little things in the dark, halfway through a movie or something, and Doug filled it with #1 diesel instead of gas. Kept right on running while hot, just wouldn't start when cold.
TFF
Well-Known Member
A proper Russian runs their Trabant on stolen diesel. A friend told me that as of the 1990s the police checked cars in traffic for full fuel tanks. Full tank meant you stole fuel because it was more than the ration you were allowed. A friend ran jet fuel from sumped planes mixed with gas and always had a full tank. He got stopped in traffic for a check. He only got to drive away because he had an uncle in the KGB.
I have another friend who was putting about 10 % jet A in his Taurus. We will call him frugal. Trying to drop his fuel cost with free sump fuel. He did get a n old Mercedes diesel and ran jet but he was going through injection pumps yearly.
I have another friend who was putting about 10 % jet A in his Taurus. We will call him frugal. Trying to drop his fuel cost with free sump fuel. He did get a n old Mercedes diesel and ran jet but he was going through injection pumps yearly.
Amateur. Shudda mixed some oil in the Jet A and saved his pump. Allegedly.
PMD
Well-Known Member
When I was in the aircraft repair biz, many decades ago, we had an office (spelled TRAILER) at the airport and got the daily flush fuel from the jet A pumps - kept us heated throughout the rather cold sub-arctic winter. It was before VW diesels, so I didn;t have a car or truck to burn it in.
mm4440
Well-Known Member
Weslake designed it for Hex, different engine.
mm4440
Well-Known Member
RM too big and expensive for this power.
