Diesel versus gas

[Hippocampus]

Have a jeep summit eco diesel. Gets 30 on the superslab at 70. Has a range of 720 miles if I stay in proximity of speed limits. Has great grunt rock crawling ( suspension let’s it rise a foot so surprisingly good at it). Diesels have great torque. Of course e has even better but lousy range. For even a coastal cruising boat range is a big deal. Gas just doesn’t have the energy density of diesel.
Have had three recalls but no other issues in 100k+ miles.

Diesel are high pressure systems c/w gas. The compression stroke ignites the fuel not a spark. So the engine must withstand that pressure. Everything in a diesel (vessel or vehicle) seems overbuilt c/w gas for that reason. There’s also usually more waste heat as well (not talking formula one engines).
Remember putting sleeves in old school diesels and getting over 1m miles out of them. Even now believe you’ll get more service life out of a diesel.
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My current boat is a totally new animal to me. In the past with small HP (<100) NA and turbo engines felt fine doing my own wrenching. On this one (common rail) will watch some else do it before attempting things beyond fluid and filter changes and belts. Think I have the concepts down but the devil is in the details. I haven’t even had a reverso in the past. Total newbie. Old enough my diesel courses weren’t on tier 4 or even 3. So yes fear prevents me at present. But knowledge makes fear go away.

Not a fan of gasoline for boats other than speedboats. Even there although current outboards are massively technologically improved service life and reliability are still a issue. Clean fuel, air and compression diesels wil go and go.

 

[rslifkin]

Typical gassers are definitely not as long lived as the more durable diesels. The lighter duty diesels aren't necessarily any better if they're pushed hard power wise though. Nothing says you can't make a gas engine that's incredibly durable, it's just not any cheaper than a diesel, so there's no demand for it.

 

[KnotYet]

As an aside, I know of no gasoline engines, other than outboards, used in boats
that are not sourced from automobile use. These engines are engineered for both
power and light weight. There are a few that are designed for trucks also.

Diesel engines used in boats are generally sourced from heavy duty trucking and
industrial applications as well as specific marine-only designs.
This is a major distinction and will show up in long term reliability.

 

[BruceK]

Did fuel injection make gas engines safer, I can see why it might.
Though it didn`t for Jaguar initially, they connected to the injectors with flexible tubing which leaked,thus the proud Jaguar owners boast "Drove it Sydney to Melbourne and back (1600 kms) and it only caught fire once!

 

[ronobrien]

This gives me a thought... Might be a good idea to keep a foam extinguisher handy. Any situation that leads to liquid gas can be foamed over the top to keep it from being exposed to air and evaporating. That would allow for a safer cleanup with less fumes.

Fortunately, most gas boats have very little pressurized in the fuel system to avoid things like that. Hardware like fuel coolers and filters are typically placed before the pump.

I will admit that I am not very familiar with marine application but gasoline fuel injected cars have the pump in the tank. The system can run as high as 60PSI and the volume is pretty high. A failure of a line in that system results in LOTS of fuel spray under moderately high pressure very quickly.

 

[rslifkin]

I will admit that I am not very familiar with marine application but gasoline fuel injected cars have the pump in the tank. The system can run as high as 60PSI and the volume is pretty high. A failure of a line in that system results in LOTS of fuel spray under moderately high pressure very quickly.

Marine systems put the pump right at the engine for both carbs and fuel injection. It's specifically because of that risk. On my carb-ed gassers, the only pressurized line is about 15" of metal hard line from the pump outlet to the carb inlet. Fuel injected stuff will have pressurized fuel rails on the intake manifold (and at higher pressure like you mentioned).



Pressurized fuel leaks in any system (gas or diesel) can be scary. Even with diesel, there's fuel under enough pressure that a leak in the wrong place will lead to a very fine mist being sprayed. If that spray hits something hot like a dry riser or non-jacketed turbo, it'll turn into a fireball very quickly. Ideally, any engine should have fuel system components routed such that they're easy to inspect and there's minimal risk of a leak under pressure spraying directly onto something hot enough to ignite the fuel.

 

[koliver]

Marine systems put the pump right at the engine for both carbs and fuel injection. It's specifically because of that risk. On my carb-ed gassers, the only pressurized line is about 15" of metal hard line from the pump outlet to the carb inlet. Fuel injected stuff will have pressurized fuel rails on the intake manifold (and at higher pressure like you mentioned).



Pressurized fuel leaks in any system (gas or diesel) can be scary. Even with diesel, there's fuel under enough pressure that a leak in the wrong place will lead to a very fine mist being sprayed. If that spray hits something hot like a dry riser or non-jacketed turbo, it'll turn into a fireball very quickly. Ideally, any engine should have fuel system components routed such that they're easy to inspect and there's minimal risk of a leak under pressure spraying directly onto something hot enough to ignite the fuel.

One of the original engines in my present boat had serial very small leaks in the high pressure fuel lines between the high pressure pump and the injectors. Those leaks were detected only when a strong light was shone on the top of the engine, while running. The mist was so fine that without searching for the leak, it was not detectable, but the top of the engine was damp with fuel. As there was no portion of the hot exhaust system in the immediate area, detection and replacement of the high pressure lines occurred without drama.