The Hvid Patent.
This is simple ... right?
A 6 HP Johnny from Quebec.
Sure, like all great and wonderful mechanical contrivances, this one is so simple a child could build it...not. Unlike the Diesel, a Hvid engine is considered an atmospheric injection system. The fuel enters the combustion chamber through non-mechanical means. Let me try to explain this using verbage from a reprint of a National Schools Service Manual dated 1937 1.
Hvid injector Graphic
Copyright Don Siefker - Used with permsission
In the diagram on the right, you can where see the fuel inlet is located. Fuel enters here under minimal pressure supplied by the small mechanical pump. The amount of fuel entering is controlled by the measuring pin (clever name). The pump is only for fuel transport and is not part of the injection system. When the piston is in the intake cycle, the fuel inlet valve opens and the measured amount of fuel flows into the fuel cup. How much fuel is measured is controlled by the knob "C" which raises and lowers the measuring pin. Now that there is fuel in the cup, how is going to get into the cylinder?
This way cool graphic makes the explanation easy. In step one the fuel has been delivered to the cup during the intake stroke.  In step two as the piston comes up on compression heated air begins to force its way through the tiny holes in the fuel cup. Some of the lighter fractions of the fuel are vaporized. Step three occurs as the piston nears maximum compression. The air now being forced into the cup is hot enough to ignite the vapor above the liquid fuel. That orange yellow cloud above the fuel is supposed to be a small explosion. Now at step four, the explosion creates enough pressure in the fuel cup to force the remaining liquid fuel through the tiny holes at very high pressure. This creates a mechanical force sufficient to vaporize the fuel as it passes through the pinholes.  Once out of the fuel cup it comes in contact with the superheated air within the cylinder and immediately ignites.
The Spraying Cup Injection Process.
Now that the fuel is on fire in the cylinder, the expanding gases from the burning fuel force the piston downward thus beginning the power stroke.  Wasn't that easy?  The actual mechanical workings are not so simple but the concept truly is. That was much of the reason for inventors really turning their efforts toward simplifying the diesel injection method, the compression ignition concept is very simple compared to all the litle evils contained within those darned gas engines!

So, now you're an expert on the Hvid injection system, right?  Good, you can help me start my 6 hp Thermoil. First, get a good nights sleep. Then get up early and have a big breakfast (No you fools, not a "Big Breakfast" ™ at that damn fast food joint, a REAL one with real eggs and bacon and hash browns and bacon and sausage and biscuits and gravy.) you're gonna need it.  I'm assuming you're in decent shape because today we're trying this with a hopper of cool water on a 90° day with high humidity...sure to break a sweat on ya!  I've got the fuel on and the greasers checked for you so hook up the crank and give it a whirl, just let me know when you're ready to drop the compression release.
Now? Ok, here it goes....Umm, that's not fast enough, it just bounces off the compression stroke.  425 psi is a pretty tough haul to over come.  Oh, sorry, I didn't realize you were taking it easy on the engine. Sure, try it again, give it all you got, can't hurt it at all.....Hey! that was close, we got a little smoke out of the intake that time. It should go the next time though. Are you feeling OK? You look a little winded.  Yeah it's a bear to spin, one more time should do it though, got your second wind yet? One more time here we go...come on! roll that big fella over....here comes the compression...whump.....whump.....WHUMP.... WHUMP....WHUMP...oh yeah she's rollin' now!  No, most people think it's a lot easier than that but you did just fine.  But you have a good grasp of why these engines struggled in the market place.  If they weren't just right, they were nearly impossible to start before passing out!
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References this Page:

1. National Schools Service Manual, 1937, Obtained from Glenn Karch,pages 5-6,
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