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Old 03-03-2014, 11:32   #1
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Why still indirect injection on boats?

Hello,

we will install a new diesel engine in our boat sooner or later.
Most of them have indirect injection, but some have direct injection, like we have on cars etc.
I think direct injection is somewhat noisy. On the other hand easyer to start?

Why is it that marine diesels mostly will have indirect injection?

Taco.
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Old 03-03-2014, 12:16   #2
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Re: Why still indirect injection on boats?

I think this is the most viable answer other than it's been that way for years, so why change it. I cut n pasted this from another site.

Indirect injection engines are cheaper to build and it is easier to produce smooth, quiet running vehicles with a simple mechanical system, so such engines are still often used in applications which carry less stringent emissions controls than road-going vehicles, such as small marine engines,
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Old 03-03-2014, 12:27   #3
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Re: Why still indirect injection on boats?

The move to the pre combustion chamber designs is driven by 1) EPA requirements, 2) Noise reduction, and 3) Fuel ecconomy. The harder starting is easily rectified by the use of glow plugs. My Beta 28 uses a "tri vortex chamber" (their version of pre combustion chamber) which gets them to the tier 4 epa requirements, is relatively quiet and never smokes. I have to use the glow plugs if it's been shut off over night but if it has run anytime in the last 8 hours or so it fires right up with out them. That's my take on it anyway. Someone else may know more.
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Old 03-03-2014, 13:11   #4
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Re: Why still indirect injection on boats?

Diesels are all direct injection I believe. Diesels turn over at very high compression which creates very high temperatures in the cylinder as the air is compressed, fuel is injected into the cylinder near TDC, the hot air ignites the diesel and the piston is forced down creating power at the crankshaft. The injectors spray fuel when they reach a high enough pressure from a primary pump which is timed to crankshaft rotation. It's an all mechanical system that works in truly horrendous conditions as long as you have reasonably clean air, clean fuel and no mechanical breakdown. Has worked on Rudolph Diesels original principles since he invented the diesel engine 2 centuries ago.

Newest diesels pioneered by VW have something called common rail injection which is still direct injection but with injectors electronically controlled from a common high pressure source. Supposedly quieter and more gasoline engine like in behavior. Unfortunately, it relies on electrickery with all the vagaries and dislike of a salty environment that come with those pesky electrons.

Personally, will stick with direct mechanical injection engine on a boat until the gumment puts a gun to my head.
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Old 03-03-2014, 13:27   #5
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Re: Why still indirect injection on boats?

Indirect refers to injecting the fuel in a pre-combustion chamber. Direct means injecting fuel directly into the combustion chamber.
Common rail brings electronic fuel injection technology into the Diesel world and yu can do many things with common rail you can't with mechanical injection, like "split shot" injection, adjustment of ignition timing etc. Common rail brought true high performance to the Diesel world, but is much more complex
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Old 03-03-2014, 13:35   #6
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Re: Why still indirect injection on boats?

Having a Dodge diesel, I can tell you that the common rail and electronic injectors are extremely sensitive to fuel contamination. Injector failures are fairly common, both from getting plugged up and from residue build up. I'm sure these reliability issues are another reason this design is not common in marine applications.
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Old 03-03-2014, 14:26   #7
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All diesel are direct injection.
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Old 03-03-2014, 14:30   #8
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Re: Why still indirect injection on boats?

http://en.wikipedia.org/wiki/Indirect_injection
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Old 03-03-2014, 14:43   #9
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Yeah but its still directly injecting into the cylinders. Just a marketing term used to make money
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Old 03-03-2014, 14:44   #10
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Re: Why still indirect injection on boats?

Quote:
Originally Posted by azsailor12 View Post
Having a Dodge diesel, I can tell you that the common rail and electronic injectors are extremely sensitive to fuel contamination. Injector failures are fairly common, both from getting plugged up and from residue build up. I'm sure these reliability issues are another reason this design is not common in marine applications.

$3,500 in parts to replace the injectors on my Duramax, been $5,000 if I had it done as they are buried deep inside of the head.
I don't want common rail on my boat
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Old 03-03-2014, 15:14   #11
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Re: Why still indirect injection on boats?

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Originally Posted by d design View Post
Yeah but its still directly injecting into the cylinders. Just a marketing term used to make money
Either you have your own personal definition for 'directly',
or you have your own personal definition for 'cylinder'


Or ... both ?
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Old 03-03-2014, 15:28   #12
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All diesel are direct injection.
No they are not....idi injects into a chamber connected to the cylinder, di injects directly into the cylinder.
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Old 03-03-2014, 16:32   #13
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How do you call it a separate chamber. It just a cavity in the head.
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Old 03-03-2014, 19:00   #14
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How do you call it a separate chamber. It just a cavity in the head.
Because that's what it's called. The prechamber on indirect injected diesels is sometimes connected to the combustion chamber only by several holes.

You are welcome to invent your own terminology if you like, but the rest of the world uses terms as several posters above have explained.

Direct injected diesel: no prechamber.

Indirect injected diesel: injection via prechamber.

For me practically the main difference is that di diesels start much more easily from cold and don't really need glow plugs or air preheaters except in very cold weather. My main engine is DI and starts if you even look sideways at the key, even in freezing weather. My genset engine, OTOH, is indirect injected and won't start without air preheating. That's because the cold prechamber absorbs the heat out of the charge - it has much greater surface area per unit of volume, than the combustion chamber of a DI engine.
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Old 04-03-2014, 12:27   #15
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Re: Why still indirect injection on boats?

Well, i like less noise and a stable running of the engine. But i do not like the glowing part.
Did you ever feel when you suddenly needed the engine, glowing took way toooo long??

Taco.
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