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Engine Manifolds: Intake and Exhaust Manifold with Working & Diagram

In this article, you’ll learn about what are Intake and Exhaust Manifold, how they work? with its Construction, Working Principle and More.

Manifolds

Manifolds are separate sets of pipes connected to the cylinder head which provide the air-fuel mixture and the exhaust gases, these are known as manifolds. It is usually made of cast iron so that it is capable to resist the high temperature of the exhaust gases.

Types of Manifolds in Engine:

Following are the two types of manifolds used in vehicles:

  1. Intake Manifold
  2. Exhaust Manifold

Intake Manifold

The intake manifold is a cast iron or aluminium tube for carrying the air-fuel mixture from the carburettor to the engine intake port. Except where the superchargers or governors are used, the intake manifold is constructed so that, when the carburettor is attached to it, the mixture can reach each cylinder.

Constructional Details with Parts:

The carburettor is mounted on the intake manifold. The intake manifold has mounted a side of the cylinder block in L-head engines and on the side of the cylinder head in I-head engines. It is situated between the two cylinder banks on V-8 engines.

Intake Manifold

A good design of intake manifold consists of the path from the carburettor to the cylinders as short and short and smooth as possible so that the fuel will not condense and collect on the manifold walls. To minimise condensation and to assist in vaporization of the gasoline in the mixture, the modern intake manifold is heated.

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Working Principle

The heat is usually supplied from the exhaust gases or cooling water, sometimes hot-spot are provided at points where the fuel strikes in the intake manifold. The heat supplied is controlled by a thermostat so that all the exhaust gases are deflected to heat the intake manifold when the engine is cold, and less heat is supplied as the engine warms up.

Intake manifold for a four cylinder engine

A single passage manifold directly connects the carburettor to the cylinder. In a four-cylinder engine, four passages each from a cylinder, submerge in one which connects the carburettor. For good distribution of the air-fuel mixture, it is desirable to have the distance of each of the cylinder from the carburettor approximately.

Dual intake manifold

The dual carburettor is usually provided with dual intake manifolds having two branches, one for each barrel of the carburettor. Each of these braches feeds half of the engine cylinders, thereby preventing overlapping of the strokes in the manifold and thus improving the uniformity of distribution.

Four barrel intake manifold

In a four-barrel intake manifold, the primary and secondary outlets for the same side of the carburettor lead the same cylinders 2, 3, 5, and 8, while the left-hand outlet leads to cylinders 1, 4, 6 and 7.

Exhaust Manifold

The exhaust manifold is a tube for removing the exhaust gases away from the engine cylinders. It collects exhaust gases from the exhaust ports of the various cylinders and conducts them to a central exhaust passage.

Constructional Details and Parts

The exhaust manifold is usually made of the cast iron. It is bolted to the side of the cylinder block on L-head engines and to the side of the cylinder head on I-head engines. On V-8 engines, there are two exhaust manifolds, one for each bank of cylinders.

Exhaust system for a six cylinder engine

In some V-8 engines, each manifold is connected to a separate exhaust pipe, muffler and tailpipe. On others, they are connected by a crossover pipe and exhaust through a common muffler and tailpipe. Fig shows an exhaust manifold for eight-cylinder in line passenger car engine.

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Working Principle

The exhaust manifold is designed to avoid overlapping of exhaust strokes, as far as possible, thus keeping the backpressure to a minimum. This is often done by dividing the exhaust manifold into two or more branches so that two cylinders will not exhaust into the same brach at the same time.

Exhaust manifold for 8 cylinder in-line car engine

Large radius bends are provided in the design to eliminate any restriction to the flow. A heat tube may also be provided to furnish heat to the built-in automatic choke unit of the carburettor. The centre portion of the exhaust manifold is often connected to the intake manifold of an in-line engine through a heat trap and exhaust damper, except where the intake manifold is water heated.

Heat control valve operation

The damper is controlled thermostatically to deflect the exhaust gases around the intake manifold. When the engine is cold, all the exhaust gases pass around the intake manifold. When the engine is warmed up, a part of the exhaust gases goes around it, and when the engine is fully warmed up none of the exhaust gases passes around the intake manifold, but goes directly to the exhaust pipe as shown fig.

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Saif M
Saif M. is a Mechanical Engineer by profession. He completed his engineering studies in 2014 and is currently working in a large firm as Mechanical Engineer. He is also an author and editor at theengineerspost.com