Common Rail Diesels Revisited

[Dockhead]

I made a preliminary decision some time ago that my next boat will have a common rail diesel, perhaps the 150hp six cylinder Yanmar.

I wonder if more experience has been accumulated by those running such engines, which can be shared?

I have long ago been convinced that turbochargers are extremely much worthwhile on sailboat diesels. Besides the advantages of thermal efficiency, noise, etc., turbo diesels allow a smaller capacity engine to have a much greater maximum power output, which means (a) you can use a more compact, lighter engine, which helps sailing performance; and (b) the engine will be happier in the typical sailboat auxilliary role, putting out no more than 20% -- 25% of its maximum output most of the time. That's because the smaller volume of a turbo engine of a given max rated power can be heated up adequately with less fuel -- at a lower power setting. It is in effect a variable-displacement engine with a much wider range of power output settings which will be healthy for the engine, something really useful in a use regime like a sailboat auxilliary which may be called on to put out 20 horsepower one day, and 100 horsepower the next.

But this is not about that. This is about conventional mechanical fuel injection vs. electronic common rail.

I would normally be inclined, for use on a boat, to the lower tech path, but I have a friend who owns a large Bosch fuel injection service shop, who convinced me that common rail is a no-brainer -- that it removes the most complex, the most expensive, and the most non-field serviceable component from the engine -- the mechanical fuel injection pump, which can be put out of action by a tiny bit of grit or tiny drop of water, rendering your engine inoperable without expensive professional service.

He told me that the fuel injector/micro-pump things on common rail engines are extremely reliable, and that you can carry spares and replace them yourself if something goes wrong. The engine computer can be kept as a spare together with a diagnostic harness and spare sensors, and you can then fix anything yourself in the field without professional service.

He said that common rail injection is actually much simpler and easier to repair, and besides that is much more reliable. This seems to me like an absolute winner for a long distance cruising sailboat. The smoother, more efficient running would just be a bonus.


Can anyone confirm any of this based on real experience?

[travellerw]

While I can't comment on the use on a boat, I can comment on the use in trucks servicing the oilfield in Canada.

Yes common rail was a fantastic innovation. However it does have some problems. The most common problem I seen was exploded injectors due to water. This was a real issue with the earlier trucks (like the 2000 Dmax). It usually occurred from trucks that were parked in heated garages during the winter months (condensation in the tank). Those problems were reduced in later years as they modified some of the design and used better filters. I think you would need to be very careful on a boat to ensure NO water gets to the injectors. Maybe someone with more mechanical knowledge than me could chime in, but I think common rail is more susceptible to water problems then old school.

The other point of bother for me would be the computer. After some cruising, I'm not comfortable with a computer controlled engine on a boat. I guess if I had a bigger budget, then I could carry a spare!

[DeepFrz]

One of the things causing damage to mechanical fuel injected engines is dirty fuel. I see so many people espousing that 30 micron filters are enough when most of the damage done to high-pressure pumps is caused by particles less than 7 micron. I have heard statements like "don't use 2 um filters as they get dirty too fast". The real solution is to clean your fuel system and keep it clean and use a properly installed fuel polishing system. That's just MHO.

[Compass790]

Originally Posted by Dockhead

I made a preliminary decision some time ago that my next boat will have a common rail diesel, perhaps the 150hp six cylinder Yanmar.

I wonder if more experience has been accumulated by those running such engines, which can be shared?

I have long ago been convinced that turbochargers are extremely much worthwhile on sailboat diesels. Besides the advantages of thermal efficiency, noise, etc., turbo diesels allow a smaller capacity engine to have a much greater maximum power output, which means (a) you can use a more compact, lighter engine, which helps sailing performance; and (b) the engine will be happier in the typical sailboat auxilliary role, putting out no more than 20% -- 25% of its maximum output most of the time. That's because the smaller volume of a turbo engine of a given max rated power can be heated up adequately with less fuel -- at a lower power setting. It is in effect a variable-displacement engine with a much wider range of power output settings which will be healthy for the engine, something really useful in a use regime like a sailboat auxilliary which may be called on to put out 20 horsepower one day, and 100 horsepower the next.

But this is not about that. This is about conventional mechanical fuel injection vs. electronic common rail.

I would normally be inclined, for use on a boat, to the lower tech path, but I have a friend who owns a large Bosch fuel injection service shop, who convinced me that common rail is a no-brainer -- that it removes the most complex, the most expensive, and the most non-field serviceable component from the engine -- the mechanical fuel injection pump, which can be put out of action by a tiny bit of grit or tiny drop of water, rendering your engine inoperable without expensive professional service.

He told me that the fuel injector/micro-pump things on common rail engines are extremely reliable, and that you can carry spares and replace them yourself if something goes wrong. The engine computer can be kept as a spare together with a diagnostic harness and spare sensors, and you can then fix anything yourself in the field without professional service.

He said that common rail injection is actually much simpler and easier to repair, and besides that is much more reliable. This seems to me like an absolute winner for a long distance cruising sailboat. The smoother, more efficient running would just be a bonus.


Can anyone confirm any of this based on real experience?

Interesting post thanks. Only question I would have is how could water or grit be less damaging in a common rail fuel injection system that runs at maybe 30,000psi & has smaller openings in injector than a mechanical system that runs at 2500 psi approx ?
Maybe ask your tech about that

[Dockhead]

Originally Posted by Compass790

Interesting post thanks. Only question I would have is how could water or grit be less damaging in a common rail fuel injection system that runs at maybe 30,000psi & has smaller openings in injector than a mechanical system that runs at 2500 psi approx ?
Maybe ask your tech about that

I have no idea, and it may be wrong. I am not an expert in this, and this idea is based just on one thing someone told me.

[Pauls]

I'd say it depends on what you think are your chances of a lightning strike. I've been hit, and my personal preference is strongly for mechanical systems.

Delivering clean fuel to the engine is well developed tech and is necessary for any diesel, common rail or mechanical. I'd suggest that the use of a day tank is a large step forward in improving the fuel system reliability.

[Dockhead]

Originally Posted by Pauls

. . . Delivering clean fuel to the engine is well developed tech and is necessary for any diesel, common rail or mechanical. I'd suggest that the use of a day tank is a large step forward in improving the fuel system reliability.

I'm a big believer in day tanks. My next boat will definitely have one.

[did-g]

Anyway for a new engine in USA, Canada and Europe it's rapidly going to be common rail with a computer or nothing, as usual pollution reg.

[Jim Cate]

One consideration, DH, is that while mechanical injector pumps are indeed complicated and not user serviceable, they seldom fail catastrophically and suddenly. Electronic controls and sensors are susceptible to sudden failure, at least in my limited experience. If one carries spares and has the knowledge, self repair (or at least replacement) is possible, but perhaps difficult to accomplish at sea and in a timely fashion.

I admire the performance of common rail engines, but have to wonder if their reliability in the hands of a yottie is really that good? If I were in your position of doing a blank page design of a new boat, it would be a hard decision for me!

Jim

[a64pilot]

OK common rail is a sort of misnomer, there are a couple of ways to do it.
The most common and the way the Duramax engine does it is with a high pressure pump, essentially nothing more than a high pressure hydraulic pump that pressurizes a "rail" or manifold if you will that all the injectors connect to, the injectors are electronically fired. It requires significant amperage to fire high pressure injectors, but you get all kinds of magic with common rail, like being able to vary injection timing and injector pulse width or even firing an initial shot of fuel to get the fire going just milliseconds before the main injection event and making Diesels spark ignition quiet, a Duramax will shut down cylinders and rotate around which one gets fuel if they overheat, in theory a Duramax will run with no cooling water, each cylinder is separately monitored as if it were a separate engine and injector pulse width and timing is adjusted for each cylinder. My 01 Duramax runs so clean that is passes 01 pollution standards with no EGR, no air injection in the exhaust and no catalyst, just a pure Diesel with no emissions equipment, not true now of course but still impressive, it met standards by strictly controlling fuel, and it is a beast let me tell you, it's not your Grandfathers Diesel. Big old Dually will embarrass most cars on acceleration.
Another way is the way Ford did it with their HEUI injectors that uses oil pressure to highly pressurize fuel in each injector effectively making each individual injector its own high pressure pump.
But an Achilles heel in common rail is fuel cleanliness, many argue 2 micron isn't nearly clean enough, the Duramax injectors suffered from dirty fuel cutting the injector tips, think water jet if you have seen one of those cut through plate steel like butter.
I have never heard of an exploding injector though. The injector tips are extremely fine to get what amounts to a fine mist of fuel spray, at 30,000 PSI plus, you only need and want tiny holes and a tiny bit of abrasive dirt will wreck one.

I have only replaced my Duramax injectors once, but if I remember correctly the injector cost was about $3,000, these are highly complicated precision machines and the price reflects it. Jim Bob at the local tractor dealer is not going to rebuild a common rail injector in the near future, I don't think.

We can argue it to death, but like four stroke outboards, it's coming, won't be long and it will be the only option.


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[a64pilot]

BTW my Dually is for sale if anyone is interested, I can't take it cruising


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[MarkSF]

I'm the owner of a VW TDi engine, the EA188. On these engines, high pressure fuel pump failures are running at something between 0.3 and 1% per engine per year. They run at something like 25,000 PSI, which makes the lubricity of the fuel absolutely critical. US ULSD is marginal for lubricity, and only 1% gasoline in the diesel can drop the lubricity below the acceptable limit. When the fuel pump fails, small particles enter the fuel system. Thanks to the recirculating fuel system, when this happens, the only way to remove the particles is to replace the entire fuel system. Pump, lines, injectors, everything. Cost is $6 to 7K at a dealer.

These are all Bosch components. They are built down to a price. By saving a few dollars on a screen that would catch the particles when the fuel pump grenades, they've instead passed thousands of dollars onto the consumer.

The other thing they saved on is any kind of effective water trap. There isn't one, so water goes straight into the pump.

I would only ever have any kind of common rail diesel if it's leased and I could then dump it when the warranty ends. This especially goes for anything with Bosch components.

May my mechanically fuel pumped Kubota soldier on for many more years. (One rebuild of the pump at 25 years old, and 3,500 hours, cost about $1000 including installation)

My friend's recent Yanmar with engine management likes to randomly generate engine faults. There's just one general "fault" light, which it likes to flash up at the most critical moment. Then you have to go looking for the code. Yes, it doesn't even tell you if it's overheating, if it's oil pressure, or what - so there's a frantic scramble for the manual every time.

[packeteer]

filtering of fuel is critical in a common rail. the fuel acts as a lubricant, and with the high pressures in use, and low tolerances, any dirt or water will do damage

[packeteer]

adding a fuel treatment can help. I drive a Toyota Hilux and the injector specialist recommends mineral 2 stroke oil at 300:1 ratio (for noisy injectors)
ps. if you ever need to replace injectors or hp pump, there are alternatives to your oem

[a64pilot]

Read this, it was almost ten years ago, but it was a very good, comprehensive test
http://www.dieselplace.com/forum/76-...y-results.html


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