Naval Diesel Engineering: The Fundamentals of Operation, Performance and Efficiency

© 2022 Onturo D. Johnson. All rights reserved.

No part of this book may be reproduced, stored in a retrieval system, or transmitted by any means without the written permission of the author.

Published by AuthorHouse 04/07/2022

ISBN: 978-1-6655-5606-4 (sc)

ISBN: 978-1-6655-5614-9 (e)

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CONTENTS

Acknowledgement

Introduction

Chapter 1 Diesel Fuel Systems and Engine Control Devices

Chapter 2 Diesel Engine Operating Practices

Chapter 3 Engine Performance and Efficiency

Chapter 4 Engine Troubleshooting

ACKNOWLEDGEMENT

The information contained herein has been adapted from the Engineman 1 & C and Engineman 3 & 2, prepared by the Bureau of Naval Personnel, NAVPERS 10543, First edition 1954 and NAVEDTRA 14331, First edition 2000, 2003, respectively: US Government Printing Office Washington, DC. 20402. The majority of this text was prepared by the Training Publications Center, Naval Personnel Program Support Activity, Washington, D.C. To the extent, this book may contain text in the public domain; the Author makes no claim of ownership. The Author is credited for text compilation and editing. United States Navy photographs taken by MC2 Dominique A Pinero, Cpl. Theodore W. Ritchie and released to the public.

INTRODUCTION

Naval Diesel Engineering: Fundamentals of Operation, Performance and Efficiency introduces the common types of fuels and the hardware systems that store, clean, transfer, and finally inject the fuel into the engine for burning, general types of installations while recognizing the fundamental starting, operating, and stopping procedures for a diesel engine under normal operating conditions aboard naval ships. The prime concern of Navy Diesel Engineers (or Engineman) is to keep the machinery for which they are responsible operating in the most efficient manner possible. Additionally, they know that engine efficiency and performance depend upon much more than just operating the throttle and changing oil at prescribed intervals. In troubleshooting an internal combustion engine, whether diesel or gasoline, this book will cover similar procedures.

You should be able to identify the characteristics of engine fuels, diesel engine fuel systems, describe unit fuel injector systems, understand how the operating speed of a diesel engine is controlled, and identify methods used to purge air from the fuel system of a diesel engine. Official illustrations and details of overhaul, maintenance, and repair have been purposely omitted from this text. The text focuses on diesel engine system components and control devices and discusses diesel engine trouble shooting and best practices for engineering professionals seeking optimal engine efficiency. This book describes some of the main causes for diesel engines failing to start, failing to maintain power after starting, overheating, and having abnormal exhaust.

Emphasis is placed on the various types of troubles that arise in connection with this machinery, the causes of these troubles, the symptoms by which they are indicated, and the remedial procedures to be followed from the Navy Diesel Engineers perspective.

CHAPTER 1

DIESEL FUEL SYSTEMS AND

ENGINE CONTROL DEVICES

I n the first part of this chapter, we will discuss the common types of fuels and the hardware systems aboard naval ships that store, clean, transfer, and inject the fuel into the engine for burning and how injected fuel maintain the engine at a set speed.

After reviewing the information in this chapter, you should be able to identify the characteristics of engine fuels in terms of properties, combustion, volatility, and turbulence. You should also be able to identify diesel engine fuel systems in terms of external fuel systems and fuel injection systems. You should be able to describe the jerk-type, distributor-type, and unit fuel injector systems in terms of design and function of components and methods of operation. Additionally, you should understand how the operating speed of a diesel engine is controlled. Finally, you should be able to identify methods you can use to purge air from the fuel system of a diesel engine.

Diesel Engine Fuel Requirements

The fuels burned in the internal-combustion engines used by the Navy must meet the specifications prescribed by the Naval Sea Systems Command. Therefore, the problem of selecting a fuel with the required properties is not your responsibility. The Navy Diesel Engineer’s primary responsibility is to follow the rules and regulations dealing with the proper use of fuels. He must strictly adhere to all prescribed safety precautions. He must also take every possible precaution to keep fuel as free as possible from impurities. Even though proper handling and use are his prime responsibilities with respect to fuel, knowing the characteristics of fuels will help him understand some of the problems in engine operation and maintenance. At the time of manufacture, fuels are generally clean and free from impurities.

However, the processes of transferring, storing, and handling fuel tend to increase the danger of contamination with foreign materials, a condition that can interfere with engine performance. Sediment and water in fuel can cause engine wear, gumming, and corrosion in the fuel system. Foreign materials in fuel can also cause an engine to operate erratically with a loss in power. For these reasons, periodic inspection, cleaning, and maintenance of fuel handling and filtering equipment are necessary. Because of the differences in the combustion processes and in the fuel systems of diesel and gasoline engines, the fuels for these engines must be refined to meet different requirements. In general, diesel engines require a particularly clean fuel; otherwise, the closely fitted parts of the injection equipment will wear rapidly and the small passages that create the fuel spray within the cylinders will become clogged. The diesel fuel must have a composition that permits its injection into the cylinders in a fine mist or fog. As injected diesel fuel enter the cylinder, it must have ignition qualities that permit the fuel to ignite properly and burn rapidly.

Volatility and Engine Operation

The ability of a liquid to change to vapor is known as volatility. All liquids tend to vaporize at atmospheric temperatures, but their rates of vaporization vary. The rate of vaporization increases as the temperature increases and as the pressure decreases (temperature is more important than pressure). In general, for a given temperature, a highly volatile fuel will vaporize more readily and at a faster rate than a fuel with a lower volatility.

The volatility of fuel affects engine-starting, length of warmup period, fuel distribution, and engine performance. When compared to diesel fuel (F-76), gasoline is much more volatile. High volatility, however, can also result in fuel dilution of the lube oil in the crankcase.

Injection, Ignition, and Combustion

The self-ignition point of a fuel is a function of temperature, pressure, and time. In a properly operating diesel engine, the intake air is compressed to a high pressure (increases the temperature), and the injection of fuel starts a few degrees before the piston reaches top dead center (TDC). The fuel is ignited by the heat of compression shortly after fuel injection starts and combustion continues throughout the injection period. Combustion in a diesel engine is much slower than it is in a gasoline engine, and the rate of pressure rise is relatively small. Immediately after injection, the atomized fuel partially evaporates with a resultant chilling of the air in the immediate vicinity of each fuel particle. However, the extreme heat of compression rapidly heats and vaporizes the fuel droplets to the self-ignition point and combustion begins. The fuel particles burn as they mix with the air. The smaller particles burn rapidly, but the larger particles take more time to ignite as heat bring them to the self-ignition point.

There is a time delay between the period when fuel is first delivered into the cylinder and when it reaches it self-ignition point. This delay is referred to as ignition delay or lag. The duration of the ignition delay is dependent upon the characteristics of the fuel, the temperature and pressure of the compressed air in the combustion space, the average size of the fuel particles, and the amount of turbulence present in the space. During this stage of combustion, the temperature and pressure within the space rise rapidly, this reduces the ignition delay in the fuel particles injected later in the combustion process versus those injected earlier.

In a diesel engine, the delay period between the start of injection and the start of self-ignition is sometimes referred to as the first phase of combustion. The second phase of combustion is ignition of the fuel injected during the first phase and the rapid spread of the flame through the combustion space, as injection continues. The resulting increase in temperature and pressure reduce the ignition lag for the fuel particles entering the combustion space during the remainder of the injection period. Remember, only a portion of the fuel has been injected during the first and second phases. As the remainder of the fuel is injected, the third or final phase of combustion takes place. The increase in temperature and pressure during the second phase is sufficient to cause most of the remaining fuel particles to ignite with practically no delay in the third phase as they come from the injection equipment. The rapid burning during the final phase of combustion causes an additional, rapid increase in pressure.

The knock that occurs during the normal operation of a diesel engine should not be confused with detonation. Generally, detonation in a diesel engine is caused by a simultaneous combustion of all particles of the fuel spray in the cylinder. Combustion (Diesel) Knock in a diesel engine is directly related to the amount of ignition delay and will take place at the end of the second phase. Diesel knock occurs from the rapid burning of large amounts of fuel (gathered in the cylinder before combustion begins). Whether combustion is normal or whether detonation occurs is determined by the amount of fuel that is ignited instantaneously. The greater the amount of fuel that ignites at one time, the greater the pressure rise and the more severe the knock. Detonation in a diesel engine is generally caused by too much delay in ignition. The greater the delay, the greater the amount of fuel that accumulates in the cylinder before ignition. When the ignition point of the excess fuel is reached, all of this fuel ignites simultaneously, causing extremely high pressures in the cylinder and an undesirable knock. Consequently, detonation in a diesel generally occurs at what is normally considered the start of the second phase of combustion. Detonation in a diesel may occur when the engine is not warmed up sufficiently or when fuel injection equipment is not operating properly. These conditions may allow excessive fuel to accumulate in the cylinder.

Even though diesel fuel must have the ability to resist detonation, it must ignite spontaneously at the proper time under the pressure and temperature conditions existing in the cylinder. The ease with which a diesel fuel ignites and the manner in which it burns determines the ignition quality of the fuel. The ignition quality of a diesel fuel is determined by its cetane rating or cetane number In fact, the cetane rating of a diesel fuel is identified by its cetane number. The higher the cetane number, the less lag there is between the time the fuel enters the cylinder and the time it begins to burn. The cetane number of a diesel fuel is derived from a comparison test. The cetane number of diesel fuel is the numerical result of an engine test designed to evaluate fuel ignition delay. To establish the cetane number scale, two reference fuels are used, cetane and heptamethylnonane. Cetane has an excellent ignition quality (100), and heptamethylnonane has a very poor ignition quality (15). The cetane rating of a fuel in which the ignition quality is unknown can be determined by a comparison of the performance of the fuel with that of a reference fuel. The cetane number represents the percentage of pure cetane in a reference fuel that will just match the ignition quality of the fuel being tested. A higher cetane number means a quicker burning of the fuel, a condition that tends to result in easier engine starting, particularly in cold weather.

Turbulence and Combustion in Diesel Engines

In both gasoline and diesel engines, the fuel and air must be properly mixed to obtain efficient combustion. In gasoline engines, mixing of the fuel and air takes place outside the cylinder. Depending upon the design of the system, mixing will occur in one of two places: (1) within the carburetor in the carburetor-type system or (2) at the intake ports in the fuel injection-type systems. In both designs, the proper mixture is forced into the cylinder to be compressed. In the diesel engine, however, fuel in the form of small particles is sprayed into the cylinder after the air has been compressed; therefore mixing takes place within the cylinder. If each particle of fuel is to be surrounded by sufficient air to burn it completely (that is, if proper air-fuel mixture is to be obtained), the air in the combustion space must be in motion. This air motion is called turbulence. Various means are used to create turbulence. Design of engine equipment and parts and, in some engines, a process called precombustion enter into the creation of proper turbulence within the cylinder of an engine.

Methods of Creating Turbulence

Fuel is distributed in the cylinders of a diesel engine by injection nozzles, which atomize the fuel and direct it to the desired portions of the combustion space. Fuel Injection creates some turbulence, but not enough for efficient combustion. In 2-stroke cycle engines, scavenging-air PORTS are designed and located so that the intake air enters the cylinder with a whirling or circular movement. The movement of the air continues through the compression event and aids in mixing the air and fuel when injection occurs.