Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How does an accelator of a vehicle work?

  1. Mar 5, 2013 #1
    Does the accelator of a vehicle control the amount of fuel injected in the engine or how does it control the speeding up of the vehicle?
    I want to know a simple way so that i make make a simple internal combustion engine.
  2. jcsd
  3. Mar 5, 2013 #2


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    Not all that easy, actually. The fuel / air supply works (in simple engines) by the air flow (pulled into the engine by the piston going down) causing a slight reduction in air pressure at the induction port. This draws a small amount of fuel through a tiny jet. This is the basic principle of a Carburettor. The more air that is admitted, the greater the pressure difference and the more fuel is drawn in. Needless to say, it is really not that simple and a real carburettor will have very accurately drilled jets (a number of them). The amount of air admitted is governed by a 'butterfly valve' which opens or closes the inlet to the cylinder (after the carburettor) and the accelerator cable controls the angle of the butterfly valve.

    Cheap model aero engines use a very simple version of this and they often (usually?) do not use spark plugs but rely on the compression to ignite the fuel / air - a Diesel type Cycle.

    I might say that the fuel supply system is probably the easiest part of a simple IC engine to make. Piston+ linkage, crank, bearings and ports demand significant workshop skills to make.
  4. Mar 5, 2013 #3


    User Avatar
    Science Advisor

    The usual approach is to have a throttle plate that controls the air flow going into the engine. Restrict the air flow and the engine slows down or even stops altogether. The throttle plate is normally located in the carburetor.


    In a Diesel engine the approach is different. In normal operation a Diesel runs with unrestricted air flow. Fuel is injected directly into the cylinder and the amount of fuel injected per cycle controls the engine power.
  5. Mar 7, 2013 #4
    Another description (for a gasoline engine): In order to make power you have to combine air and fuel, and burn it. However, for every part of fuel, you need ~14 parts of air, so by far the biggest problem is how much air you can fit into the engine.

    That's the main reason for why the pistons, cylinders, runners, exhaust...indeed the engine, is as big as it is.

    In order to fit in as much as possible, you also make the air passages smooth and just design everything so that as much air as possible can make it from the atmosphere to the cylinder in the split second that it has to do so.

    In order to control the power, you simply place a controllable restriction somewhere in the system so that less air fills the cylinders. You control this restriction with the accelerator. In modern systems, the computer adds the appropriate amount of fuel. In old-school systems, a carburetor was used.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook