Is a V-8 engine better than a V-4 engine? (all else being equal...HP, torque, etc)

General Questions
#61

simplicity. they just want to fit the engine into the space between the tractor wheels, and since 3 cyclinder diesel is smooth enough, they use it… Diesel cylinders can be any size, since all the diesel is ignited at the same time, by the compression.

Petrol gas spark ignition… the fire starts at the spark plug, and then takes time to travel down.
So for gas/petrol, with the spark plug ignition, ~500 cc cylinder size is the sweet spot, and its terrible to go larger limits the RPM too much… the flame front has to travel from the spark plug down through the cylinder… the larger cylinder the longer it takes…

Motorbikes are so efficient, they can choose to be a bit less efficient by using smaller cylinders…to get higher RPM …shorter burn time for the flame front to set the whole cylinder’s worth alight.

#62

Interesting point. There are compression ignition cylinders big enough for people to fit into (e.g. 38" bore, 98" stroke) in the biggest marine diesels. And also finger tip size, for model airplanes (IIRC these aren’t exactly diesels for some reason, but they’re still compression ignition).

#63

Indeed. Here is a 109,000 HP diesel engine:

Here is the crankshaft:

#64

Ya know, … there’s big and then there’s Industrial Strength Seriously BIG.

#65

Is that a turbocharger in the upper right? It’s bigger than my car!

#66

I think it might be. Here is a picture I found of the turbocharger (and yeah, it is bigger than your car):

#67

I saw a comment that said this engine doesn’t move the ship, it spins the earth in the other direction.

Also, I think that is half the engine. They take another one of those and bolt them together into one engine.

#68

The wiki on Wartsila

suggests they come in 3- to 14-cylinder configurations, and that’s the real high powered one. The first pic you showed seems to be a 6- or 7-cylinder module.

#69

Damn.

#70

I am no expert but is that a supercharger or a turbocharger? I do not see a hot/cold side like you would in a turbocharger. Since these engines have low RPM perhaps exhaust force is not sufficient for a turbocharger so they use a supercharger (only speculating).

Note: I am far, far, far from knowledgeable when it comes to engines. I know their basic operation but that is where it ends.

#71

I think the guy on the left is standing on compressor and the guy on the right is on the turbine. Though the more I stare at it, the less sure I am and it could they other way around.

#72

Yeah…imagine the belt needed to run a supercharger that size. Probably doesn’t exist and if it did…have fun fitting it.

#73

The could use a gear drive instead of belt. But yeah, I’m pretty sure that’s a turbo.

#74

IMO that’s correct. As I decode it, the lighter colored cylinder at left is the air intake filter screen. The compressor output is at lower left. The exhaust intake is at far right; we can see the flange with umpteen bolts around the perimeter that connects to the exhaust manifold. The rectangular port facing us on the right is the exhaust that leads up to the ship’s stack. We can see it facing more or less upwards on the engine sitting on the trailer.

I’m going to guess the turbo doesn’t produce huge boost, but it does enough to pay for itself.

#75

I got one of these for my Scion tC. This is the greatest car on earth but it needed a turbo. The installation instructions sounded like they were translated from German to Chinese to English but I finally got it installed. The turbo lag is awful. I can floor it and I sill have time to download all of Fast and Furrious: Tokyo Drift on my phone before the turbo spools up. Even then, I don’t think I’m getting the full 45,000 horsepower it was supposed to add. Worse yet, having 98.7% of the weight over the front wheels has made my Scion understeer really bad. Now I need wider tires and a stiffer rear sway bar. I told the seller I wanted to return it but he says it just needs a tune. I should have bought a JDM R32 Nissan Skyline GT-R instead of this turbo. I wish I could give it zero stars.

#76

The smallest I’m aware of is the Cox 0.049 cubic-inch two-stroke engine, which uses a catalytic glowplug for ignition. To start it, you plug the glowplug into battery to preheat it, then you spin the prop with your finger (if you’re brave), a stick, a spring, or an external electric starter. The hot glowplug is coated with catalytic material (platinum), and the combination is enough to ignite the fuel when the piston is somewhere close to top dead center. Once it starts, you adjust the fuel mixture so ignition happens at about the right time. At that point you can disconnect the battery, and the heat of combustion will keep the glowplug warm enough for the next cycle.

This page says the .049 operates in the same manner as a diesel engine:

But that’s not correct. The glowplug is required for ongoing operation, so they’re not true diesels in the same sense as a heavy-duty truck engine. The adiabatic heating due to compression is not enough by itself to ignite the fuel; the glowplug has to be there. Here’s a more detailed explanation of model-scale glowplug engines:

#77

Well, I hear you, I understand the glow plug operates in an electrically powered mode to start, and a fuel heated mode to run, and is always needed. But it is compression ignition, even if locally around the glow plug to begin.

The Wikipedia article on “diesel engine” begins:
" The diesel engine , named after Rudolf Diesel, is an internal combustion engine in which ignition of the fuel is caused by the elevated temperature of the air in the cylinder due to the mechanical compression; thus, the diesel engine is a so-called compression-ignition engine (CI engine). This contrasts with engines using spark plug-ignition of the air-fuel mixture, such as a petrol engine(gasoline engine) or a gas engine(using a gaseous fuel like natural gasor liquefied petroleum gas)."

I think this makes it sound like the model engine IS a true diesel, though I’ll grant there is some variety in diesel engine designs. At least, reading this, I don’t get why it’s not a true diesel.

#78

I think at this point it comes down to the No True Diesel fallacy. Until / unless we can agree on exactly which set of attributes represent all diesels and nothing but diesels we’re kinda stuck.

The glowplug is essentially a way to have the compression ignition occur earlier / at lower temperature / at lower pressure as a result of both chemical catalysis and a local thermal hotspot to get the fire started. If either of those things is absent, a glowplug engine will not start or run. The basic 8th-grade textbook schematic of a diesel lacks both of those attributes. So do most real world diesels.

OTOH, glowplug engines are also different from spark-ignition engines that rely on a carefully timed intermittent / momentary source of ignition.

My bottom line: Glowplug engines are a semi-hermaphrodite between them both.

#79

Agreed. Except on the use of this term. Sorry for the tangent, but some of my work is in support of people who are intersex, for which this term is pejorative. So I just had to stop and point it out, as few people seem aware. And it comes up so rarely in engine discussions…

Spreading awareness.

Thanks!

#80

I had no idea. Thank you.

Not trying to shoot the messenger or the message here. But I wonder …

So what terms can / should we use for gizmos combining features of two archetypically disjoint genres that haven’t already been applied somehow to some aspect of humans or their social groups? Because it seems as if any term applied to any person or group, whether by themselves or somebody else, can be construed as giving offense to some people at some time.

IOW, it’s becoming as if we need a set of terms that are off-limits to apply to people or groups of people so we can safely apply them to everything else. And likewise a disjoint set of terms that are off limits to apply to anything else so we can safely apply them to people or groups of people.

Getting universal agreement on these two term lists is of course impossible. Much less universal agreement to abide by the lists’ strictures.