Engineering workshop

Index Key: ENG048
Author: gerald j ballmann
Subject: Diesel engine combustion efficiency.
1) What limits the compression ratio of a diesel engine?
2) What is the best fuel to use in a diesel engine for maximum efficiency?

Response #: 1 of 2
Author: daniel n koury jr
The compression ratio for a particular engine is limited by how strong the
engine block is. Too much pressure (compression) and something will break.
The best fuel will also depend on the design of the engine. But as a
general rule, the greater the energy content of the fuel, the greater the
efficiency (at least in terms of miles per gallon or km per liter). Water
has a low energy content and would not make a good fuel for example.

Response #: 2 of 2
Author: david r munoz
The limits to compression ratio are based on the knock limits of the fuel.
Knock is the term used to describe the auto ignition that occurs when a fuel
ignites because the pressure in the cylinder is such that combustion occurs.
In a spark ignited…

The burning of fuel in an engine cylinder (2 stroke or 4 stroke diesel engine) will result in the production of power at an output shaft, some of the power produced in the cylinder will be used to drive the rotating masses of the engine.

Typical indicator diagram for a 2 stroke engine is shown in figure below. The area within the diagram represents the work done within the cylinder in one cycle.
The area can be measured by an instrument known as 'Planimeter' or by the use of the mid ordinates rule. [On modern engines this diagram can be continuously taken by employing two transducers, one pressure transducer in the combustion space and other transducer on the shaft. Through the computer we can thus get on line indicated diagram and power of all cylinders.]

The area is then divided by the length of the diagram in order to obtain mean height. This mean height, when multiplied by the spring scale of the indicator mechanism, gives the indicated mean effective pressures for the cylind…

Mount he fuel injector in its test rig and connect up the oil supply. Under no circumstances should hands be placed under the injector spray. The high velocity oil jet can penetrate the skin and cause blood poisoning. With the injector priming valve open, operate the hand pump to prime the injector. Once the fuel flows from the priming valve it can be closed.

Oil ContainerPressure GaugeShut off valvePump leverTest pumpInjectorHigh Pressure fuel pumpOperate the pump rapidly for several strokes. The injector should open with a high pitched chatter and fuel should be emitted in a fine cloud. After the injector opens, check to make sure the pressure does not fall off too quickly.

To test for the tightness between the nozzle needle and seat, operate the hand pump slowly to gradually increase the pressure until it is just below opening pressure. Maintain the pressure for a few seconds and ensure injector is not dripping.

To test for tightness between needle and guide, operate the hand pu…

Diesel Engine is a type of internal combustion engine (one from which work is obtained by compression of the fuel within the cylinders themselves) which operates on the constant pressure or diesel cycle principle. Fuel is admitted directly into the cylinder and combustion takes place as a result of the heat of compression.
In these engines, gas pressure in the cylinder acts on the piston, forcing it down during the power stroke to drive the crankshaft through connecting rods. The extreme positions reached by the piston correspond to the top and bottom dead center positions (TDC & BDC) of the crank and are so designated. The inside diameter of the cylinder is the bore. The distance traveled between dead centers (TDC &BDC) is the stroke, corresponding volume is the swept volume, or displacement, of the cylinder. The cylinder volume above piston when piston is at TDC is called clearance volume. Similarly the cylinder volume above piston when piston is at BDC is called cylinder v…

CAUSE OF FAILURE 6...mishandling during installation/removal/testing, water/moisture leaking past injector plug connector, inadequate vehicle maintenance, improper storage.EFFECTS OF FAILURE 6...no firing, intermittant firing, or weak firing of injector due to poor electrical conductivity , poor engine performance, poor fuel economy. engine overheating, potential engine damage, overfueling of other cylinders as 02 sensor reads excess 02 in exhaust and adjusts "rich" to compensate.

CAUSE OF FAILURE 5...fuel additives "baked" on pintle or orifice, weak injector return spring, rust/corrosion internal to injector body.EFFECT OF FAILURE 5...leaking fuel injector, after shutdown fuel leak in affected cylinder (causing hard start), overfueling of affected cylinder with resultant underfueling of remaining cylinders in the "closed loop" system, potential for damage to O2 sensor or "cats".

CAUSE OF FAILURE 4...Defective manufacturing and testing, overheating of injector from cooling system failure, ignition system failure, incorrect timing, improper "handling" during installation/removal/storage/shipping, etc.EFFECT OF FAILURE 4...High potential for engine fuel fire (dependent on location of leak), poor engine performance, poor fuel economy, potential for engine damage.