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Old 09-09-2015, 09:15 PM
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Agreen Agreen is offline
Motorized Bicycle Elite Member
Join Date: Feb 2013
Location: Goose Creek, SC
Posts: 630
Default Re: Anyone thought about a diesel bike?

Diesel carburetors...

Glow plug ignition...

I don't like being a nay-sayer, but it's not going to work. Converting a china girl to diesel is not impossible, but extremely impractical. It's like converting a cat to a dog.

But let me explain a couple things first. (I'm really not trying to be a jerk here, I genuinely want to help!)

Diesel engines don't have a carburetor. They can't. Diesel engines control the speed of the engine by fuel flow, not air flow. As a matter of fact, diesels don't even have a throttle plate! That's why cars and trucks with diesel engines have to use power steering assist brakes. Gasoline engines create vacuum when the throttle isn't fully open, so the brake booster uses vacuum to assist the brake force. Diesels don't have a throttle, so at any speed the manifold pressure is always zero.

So how do you control speed with fuel flow? Diesel engines use a very special high pressure fuel pump called an injection pump. It pressurized the fuel to somewhere between 3000 to 15,000 psi (depending on the engine or manufacturers) and a port gets uncovered at the right time to deliver the high pressure fuel to a poppet valve, known as an injector. The injector is positioned directly in the combustion chamber. Fuel flow is throttled through a valve, and engine speed is directly related to fuel.

At idle, there is very little fuel flow. There's a lot of air, and not a lot of fuel. That's why they're so loud at idle. That clackety clackety noise is detonation! But don't worry, the engine is designed to handle it! They have BEEFY components. Cast iron cylinder blocks, huge cooling channels, cast iron heads, mega-beef conrod, etc. They're beasts. That's why they last forever! Plus, the fuel is an awesome lubricant, so it gets lubricated from both sides of the piston as well.

As far as ignition is concerned, it's as easy as it gets. The compression ratio is in the neighborhood of 25:1. So when the air is drawn in, it fills the chamber with ONLY fresh air. No fuel. The piston starts heading up and compresses the bejeezus out of the air, which superheats the air. So hot. The injection pump sends fuel to the poppet, and a blast of atomized diesel comes rushing in to the hot air. Boom. And the rest of the cycle is the same for gas 4 strokes.

Glow plugs are used to preheat the air coming in so it makes the engine easier to start cold. It does not sit in the combustion chamber. It's in the intake.

Now, you may ask "but aren't there 2 stroke diesels?"

Of course there are. But they utilize a "scavenging air blower", which is effectively a supercharger. It blows exhaust gasses out the exhaust ports so that the piston only has to compress fresh air.

So there. MAJOR differences, and not too practical to try and figure out on a bicycle.

I hope this has been educational for everyone reading.

I like your way of thinking, though, longboard. If you can find a small diesel (they're out there) then you may be on to something...
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