Does the 35:1 ratio refer to 35 X the minimum air required for perfect combustion ?
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Yanmar 2GMF cold starting
- Thread starter Tom Fritz
- Start date
No, it is by weight. I'm not sure what the magic number is for diesel. The magic number for gasoline is 14.7:1 but I bet you knew that.
The following is from a Google search.
The stoichometric air/fuel ratio for diesel is about 14.6:1 very close to gasoline. As the fuel ratio approaches this 15:1 it will begin to smoke. The diesel engine may run a lean as 70:1, I didn't realize/remember it being that lean.
The stoichometric air/fuel ratio for diesel is about 14.6:1 very close to gasoline. As the fuel ratio approaches this 15:1 it will begin to smoke. The diesel engine may run a lean as 70:1, I didn't realize/remember it being that lean.
Still see it on the inside of my shirtsleeve where I used it as a crib note when I wrote the exam.
I can see the large change in ratio due the difference in fuel required to idle the engine as opposed to running WOT.
With that information at my fingertips, I know that checking and re-installing the mixing elbow on my Yanmar 2GM20F will now be much, much easier
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Throttle position also affects injection timing. My Yanmar 2QM15 engine manual suggests fully opening the throttle for cold weather starting and immediately pulling the throttle back after the engine starts.
My Volvo Penta 2002 start process when cold was to pull and hold the kill handle, open the throttle and then release the kill handle. Crack engine and reduce throttle after the engine started. It would start at 35f if I follow the procedure, but it would not if I just open the throttle. That engine didn't have glow plugs or any type of heater. I believe that procedure bypassed a mechanical fuel limiter inside the pump, it my have altered the timing too (probably did).
The internet seemed to hate the VP 2000 series but I never had any issues with mine.
The internet seemed to hate the VP 2000 series but I never had any issues with mine.
This is what I’ve been told also. Wide open throttle, then immediately throttle down to idle speed when it starts. My Yanmar 2GM is always slow to start on a 50° or 60° morning, but will fire right up if it’s 90°. Makes sense when ignition comes from the heat generated by compression.
Alright, you people started it so I'm going with the flow on cold weather starting.
The engine is a 1998 year of manufacture, Yanmar 2gm20f. I have a bit of a problem with starting in cold weather about 5°C (41°C). The easiest start is to pull the engine stop and then crank the engine for about 5 sec. Push the stop in and then start the engine with the usual hacking and coughing and runs well from there on. However, if we're at anchor in the middle of winter, it is freezing in the cabin in the morning. We may do this for up to three days without ever starting the engine. When we do start, no priming, no throttle, no nothing and the engine starts in about 1/2 a revolution. If the engine is at the dock for a week, same more difficult starting. The engine NEVER starts in 1/2 a revolution in the middle of summer after sitting for a week. And that's in a heat wave.
My suspicion is that after running and being shut down for a period of up to three days, the rings remain slathered in oil and ensure a perfect seal for compression when starting. I've often thought about installing a hand powered oil pump to oil the rings before starting the engine. I'm sure I'd have no problem wedging it into the Nike shoe box the engine sits in.
I don’t understand how turning the engine with the start lever pulled helps, at least on a Yanmar. The Yanmar stop lever just shuts off fuel; it’s not a decompression lever. So how does cutting the fuel source help speed starting?
I don't understand it either. Volvo Penta published the instructions I used on my VP2002. It definitely made a difference. I've never heard or read of a similar procedure for a Yanmar. Maybe the fueling mechanism, injector pump and governor, are the same.
I thought the idea is to move the pistons in the cylinders, without cold fuel being sprayed in, to generate some heat…then introduce the fuel…but that is just my hypothesis.
Greg
I guess that's possible. Not how it works on the VP 2000 series.
Interesting idea. I don’t know if the thermal mass of a fraction of an ounce of atomized fuel is much compared to the block, but I guess it’s as good of a theory as any.
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 21,202
Rotating the engine would allow the pumping of oil to lubricate the engine parts. The compression of air no fuel might heat the chamber a bit. Adding fuel to the rotating system could start the engine. Not unlike getting a car rolling down hill before turning the key and popping the clutch...
When my Perkins started there was no glow plug needed. Winter or Summer.
When my Perkins started there was no glow plug needed. Winter or Summer.
IMO, rolling over the engine without allowing it to start gives the engine an opportunity to send oil to the piston rings and ensure they are able to seal. Dry rings do not without oil. With the rings wet and sealed, there is better compression and higher temperatures. The point I was making is that when the rings are wet, an ice cold engine (at least my engine) will start in 1/2 a rev. Conversely, if the rings are unused for a week or better, they drain most of the oil that was in them resulting in lower compression.
Yanmar publishes instruction on starting an engine which has not been used for a while :
They do this for the purpose of ensuring there is a supply of oil to all surfaces in the engine. Subsequent to that procedure, I found that starting the engine became much easier. The only explanation I can see for the faster starting is the wetting of the piston rings.
Without circulating the oil first, starting is a series of coughs, false starts, and dying. Repeat again until the engine starts. With oiling prior to starting, starting consists of one start and it stays running.
This is just my findings on a Yanmar in conjunction with the factory instructions. Other's experience may differ.
There is a throttle lever at the controls and it needs to be opened. The air flows through the air intake tube and enters through the engine's intake valves. The more fuel, the more air is intake to maintain the correct air fuel mixture and reduces the pressure required by the pistons to enter the air. This flow allows the engine to crank faster. That is how it helps.
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That's correct for a gasoline engine.
The picture is of a diesel that's running as I type this. Notice the complete lack of a throttle plate assembly under the air filter, because it doesn't have one.
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Would love to hear your explanation why opening the throttle lever facilitates cranking the engine.
@Benny17441 , pardon me for asking, but for my own clarity could you please advise the make and model of the engine which you have in your boat and are discussing. Thanks.