What is a diesel engine, and how does its ignition process differ from a petrol engine?

A diesel engine is a type of internal combustion engine that uses compression ignition. This means it ignites diesel fuel solely through the high temperature generated by compressing air within the cylinder, unlike petrol engines which rely on a spark plug to ignite the air-fuel mixture.

Who invented the diesel engine, and what is it named after?

The diesel engine is named after its inventor, the German engineer Rudolf Diesel. His groundbreaking work led to the development of this compression-ignition engine.

How does a diesel engine achieve ignition without a spark plug?

Diesel engines achieve ignition by compressing air to very high pressures and temperatures within the cylinder. When diesel fuel is injected into this superheated air, it spontaneously ignites due to the extreme heat.

What is the primary method diesel engines use to control torque output?

Diesel engines control their torque output by precisely regulating the amount of fuel injected into the cylinders. Unlike gasoline engines that often throttle intake air, diesel engines typically maximize air intake and adjust fuel volume to manage power.

What makes diesel engines generally more efficient than other combustion engines?

Diesel engines achieve higher thermal efficiency primarily due to their high compression ratios and lean-burn operation, which allows excess air to help dissipate heat. They also avoid fuel loss during valve overlap, a phenomenon that can occur in some gasoline engines.

What types of combustion cycles can diesel engines operate on?

Diesel engines can be designed to operate using either a two-stroke or a four-stroke combustion cycle, depending on the specific application and design requirements.

What were the initial applications of the diesel engine after its invention?

Initially, diesel engines were developed as a more efficient alternative to stationary steam engines. By the 1910s, their use expanded to submarines and ships, and later to locomotives, heavy equipment, and automobiles.

What inspired Rudolf Diesel to develop his engine?

Rudolf Diesel was inspired by lectures from Carl von Linde about the inefficiency of steam engines and the theoretical potential of the Carnot cycle. He was also influenced by a fire piston, a device demonstrating the principle of ignition through rapid air compression.

What was the core concept of Rudolf Diesel's initial 1893 "rational heat motor" proposal?

Rudolf Diesel's initial concept, outlined in his 1893 essay, proposed a "rational heat motor" that would utilize a constant temperature cycle with isothermal compression. This theoretical design required extremely high compression ratios, which proved impractical for actual engine construction.

What is the typical compression ratio range for a diesel engine?

Diesel engines typically operate with a compression ratio ranging from 15:1 to 23:1, which is significantly higher than that of most gasoline engines.

Why can diesel engines use higher compression ratios than gasoline engines without pre-ignition?

Diesel engines can achieve higher compression ratios because they only compress air initially, introducing fuel later in the cycle. This prevents the fuel-air mixture from igniting prematurely, a problem known as pre-ignition or detonation that limits compression in gasoline engines.

What causes the characteristic "diesel clatter" noise?

The distinctive noise known as "diesel clatter" is primarily caused by the rapid ignition of the injected fuel due to the high temperature of the compressed air. This sudden combustion creates a pressure wave that results in a knocking sound.

What are some methods used to reduce diesel engine noise?

Diesel engine noise can be reduced through techniques such as indirect injection, pilot injection, precise control of injection timing and rate, optimizing the compression ratio, and using diesel fuels with a higher cetane rating.

Why are diesel engines generally heavier than comparable gasoline engines?

Diesel engines are typically heavier because they must withstand higher internal pressures generated during the compression stroke. This necessitates stronger, and therefore heavier, engine components.

What are the main pollutants found in diesel exhaust gas?

Diesel engine exhaust gas contains pollutants resulting from incomplete combustion, including carbon monoxide, hydrocarbons, particulate matter, and nitrogen oxides.

How is torque output regulated in a diesel engine?

Torque output in a diesel engine is regulated by a governor that controls the amount of fuel injected. Modern engines utilize electronic control units (ECUs) that process sensor data to precisely manage fuel delivery based on operating conditions.

What is the difference between Direct Injection (DI) and Indirect Injection (IDI) diesel engines?

In Direct Injection (DI) diesel engines, fuel is sprayed directly into the combustion chamber, often within a specially shaped piston bowl. Indirect Injection (IDI) engines inject fuel into a pre-combustion or swirl chamber connected to the main cylinder, which aids in mixing and turbulence.

What are the advantages and disadvantages of Indirect Injection (IDI) diesel engines?

IDI diesel engines are known for smoother, quieter operation and can be built with simpler mechanical injection systems. However, they generally have lower efficiency due to increased heat loss and often require glow plugs for cold starts.

What is a Common Rail (CR) injection system?

A Common Rail (CR) injection system utilizes a high-pressure fuel reservoir, the "common rail," which supplies fuel to injectors. This system allows for precise control over fuel pressure and multiple injection events per cycle, leading to improved efficiency, reduced emissions, and quieter operation.

What is a unit injector system in diesel engines?

A unit injector system combines the fuel pump and injector into a single component mounted above each cylinder. This design eliminates high-pressure fuel lines, ensuring consistent injection, though it has largely been replaced by common rail systems in modern vehicles.

What is air-blast injection, and why is it less common today?

Air-blast injection was an early diesel injection method that used compressed air to atomize and inject fuel. It was largely replaced because the system was heavy, slow to respond to load changes, and thus unsuitable for vehicles.

How are diesel engines classified by their rotational speed?

Diesel engines are categorized by rotational speed into three groups: high-speed (over 1,000 rpm), medium-speed (300-1,000 rpm), and low-speed (under 300 rpm).

What are the typical applications for high-speed, medium-speed, and low-speed diesel engines?

High-speed diesel engines are commonly found in trucks, buses, cars, and small generators. Medium-speed engines are used in larger generators, locomotives, and ship propulsion, while low-speed engines are primarily used for powering large ships.

What type of fuel is typically used in modern low-speed marine diesel engines?

Modern low-speed marine diesel engines typically operate on highly viscous fuel oil, which is different from the diesel fuel used in most road vehicles.

What is scavenging in a two-stroke diesel engine?

Scavenging in a two-stroke diesel engine is the process where fresh air is pushed into the cylinder by a blower or compressor to expel the exhaust gases, as the intake and exhaust ports are open simultaneously for part of the cycle.

What are the main advantages of diesel fuel compared to gasoline?

Diesel fuel offers advantages such as lower cost, better lubrication properties, higher energy density, and a reduced fire risk due to its higher flash point and lower vapor pressure compared to gasoline.

What does the cetane number of diesel fuel indicate?

The cetane number of diesel fuel indicates its ignition quality, specifically how readily it ignites under compression. A higher cetane number leads to smoother combustion and less engine noise.

What is the primary challenge in developing "low heat rejection" diesel engines?

A significant challenge in developing low heat rejection diesel engines, which use thermal barrier coatings to improve efficiency, is finding lubricants that can withstand the higher operating temperatures without degrading.

What are the key development goals for diesel engines in recent years?

Recent development goals for diesel engines primarily focus on improving exhaust emissions, reducing fuel consumption, and increasing the overall lifespan of the engine.

What are the main advantages of using diesel engines in aircraft?

In aviation, diesel engines offer benefits such as better fuel efficiency, lower carbon emissions, the ability to use less volatile fuels like Jet-A, and a reduced risk of fire compared to gasoline engines. They also eliminate the need for lead additives in avgas.

What is the significance of the Packard DR-980?

The Packard DR-980, developed in 1929, was America's first aircraft diesel engine. It demonstrated advantages like improved high-altitude performance and reduced fire risk, though its development was ultimately hampered by various issues.

What is the "M-System" in diesel engine design?

The M-System is a diesel engine design, patented by J. Siegfried Meurer, that features a central sphere combustion chamber located within the piston, contributing to efficient combustion.

What is the main benefit of diesel engines not using intake air throttling?

The absence of intake air throttling in diesel engines contributes to their excellent fuel efficiency, particularly at lower loads, as they can maintain maximum air intake while adjusting fuel delivery.

What type of fuel is commonly used in stationary diesel engines for electricity generation?

Stationary diesel engines used for electricity generation typically run on diesel fuel and are often designed to operate at a fixed rotational frequency to match the power grid's frequency requirements.

What is the primary challenge associated with diesel fuel in cold weather conditions?

Diesel fuel can "wax" or "gel" in cold weather, causing solidification in the fuel system, particularly in filters, which can lead to the engine stopping.

What is the purpose of an intercooler in a turbocharged diesel engine?

An intercooler cools the compressed air from the turbocharger before it enters the engine cylinders. Cooler, denser air allows for more oxygen in the combustion chamber, improving efficiency and power.

What is the significance of the MS Selandia in maritime history?

The MS Selandia, launched in 1912, was the first ocean-going ship to be powered by diesel engines, marking a pivotal moment in the adoption of diesel technology for large vessels.

What was the first mass-produced diesel engine for passenger cars?

The Mercedes-Benz OM 138, introduced in 1935 and rated at 45 PS (33 kW), was the first mass-produced diesel engine specifically designed for passenger cars.

Why are diesel engines permitted in the American National Radio Quiet Zone?

Diesel engines do not require high-voltage ignition systems like petrol engines. This lack of radio frequency emissions makes them suitable for environments where electromagnetic interference must be minimized, such as the National Radio Quiet Zone.

What is the typical fuel standard for modern passenger car diesel engines in Europe?

Modern passenger car diesel engines in Europe typically use diesel fuel that conforms to the EN 590 standard, which defines critical properties like cetane number, density, and sulfur content.

What is the primary cause of the characteristic noise in diesel engines, often called "diesel clatter"?

Diesel clatter is caused by the rapid ignition of fuel as it's injected into the hot, compressed air in the cylinder, creating a pressure wave that sounds like knocking.

What is the function of a glow plug in a diesel engine?

Glow plugs are heating elements used in some diesel engines, particularly in cold conditions, to preheat the combustion chamber, aiding in the vaporization and ignition of the fuel.

What are the main advantages of supercharging or turbocharging diesel engines?

Supercharging and turbocharging significantly increase the efficiency and torque output of diesel engines by forcing more air into the cylinders. This is beneficial because diesel engines can handle the increased air without the risk of knocking or detonation.

What are some major manufacturers of diesel engines globally?

Prominent diesel engine manufacturers include MTU, MAN, Wärtsilä, Rolls-Royce Power Systems, Cummins, Caterpillar, General Electric, Volvo Penta, Mitsubishi, and BMW.

What is the typical lifespan of modern heavy-duty diesel engines used in lorries?

Modern heavy-duty diesel engines, often designed with an undersquare configuration for longevity, can achieve lifespans of up to 1,200,000 kilometers (750,000 miles), representing a significant increase over older designs.

How did diesel engines replace steam engines in locomotives?

Diesel engines have largely replaced steam engines in locomotives worldwide, primarily through diesel-electric systems where the diesel engine powers an electric generator that drives the traction motors.

What is the significance of the Junkers Jumo 205 engine in aviation history?

The Junkers Jumo 205 was a highly successful aviation diesel engine, with over 900 units produced by World War II, noted for its efficiency and power, and was used in various aircraft and airships.

What is the purpose of a catalytic converter or diesel particulate filter in diesel exhaust systems?

Catalytic converters and diesel particulate filters are exhaust gas treatment technologies designed to remove pollutants like particulate matter and nitrogen oxides from diesel exhaust, significantly reducing harmful emissions.

What is the difference between a diesel engine's fuel and a petrol engine's fuel in terms of ignition quality?

Diesel fuel is characterized by its cetane number, which measures its ignition quality under compression. Petrol, on the other hand, is characterized by its octane rating, which measures its resistance to knocking or premature ignition.

What is the role of the crankshaft in a diesel engine?

The crankshaft converts the reciprocating (up-and-down) motion of the pistons into rotational motion, which ultimately drives the vehicle's wheels or other machinery. It must be robust to handle the high forces generated by the diesel combustion process.

Diesel Engine Wiki: The Diesel Engine: Powering Progress Through Compression

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Introduction

Compression Ignition

The diesel engine, named after its inventor Rudolf Diesel, is a type of internal combustion engine. Its defining characteristic is the ignition of diesel fuel through the elevated temperature of air achieved via mechanical compression within the cylinder. This process classifies it as a compression-ignition (CI) engine, distinguishing it from spark-ignition engines like gasoline or gas engines.

Efficiency and Power

Diesel engines are renowned for their superior thermal efficiency compared to other practical internal or external combustion engines. This is attributed to their high expansion ratios and lean-burn operation, which allows for efficient heat dissipation. While not as efficient as combined cycle gas turbines, their compact nature makes them suitable for a vast array of vehicles and applications.

Industrial Impact

Initially developed as a more efficient alternative to steam engines, the diesel engine has become a cornerstone of modern industry. Its applications span from marine propulsion and locomotives to heavy equipment, power generation, and increasingly, light aircraft and unmanned aerial vehicles.

History

Diesel's Vision

Rudolf Diesel conceived of a highly efficient engine working on the Carnot cycle, inspired by lectures and the principle of the fire piston. His 1893 essay, "Theory and Construction of a Rational Heat Motor," outlined his ideas, though early iterations faced significant technical challenges and criticism. The initial concept of constant-temperature combustion evolved into the more practical constant-pressure cycle.

Early Development

The first prototype engine, built in Augsburg in 1893, underwent numerous modifications. By 1897, Diesel's third prototype achieved a notable effective efficiency of 26.2%, marking a significant breakthrough. This success paved the way for commercialization, with patents secured and manufacturing agreements established, leading to Diesel becoming a millionaire by 1898.

Key Milestones

The diesel engine's development is marked by continuous innovation. Key milestones include the first two-stroke engines, the introduction of turbochargers and intercoolers, the advent of direct injection, common rail systems, and advanced electronic controls. These advancements have consistently improved efficiency, power, and emissions control.

1893: Rudolf Diesel publishes his foundational essay.
1897: First successful prototype demonstrates 26.2% efficiency.
1903: First diesel-powered ships launched.
1910s: Widespread adoption in submarines and locomotives begins.
1930s: Introduction into passenger cars and development of aviation diesel engines.
1970s-Present: Advancements in electronic controls, common rail, turbocharging, and emissions reduction technologies.

Operating Principle

The Four-Stroke Cycle

The diesel engine operates on a four-stroke cycle: Intake, Compression, Power, and Exhaust. Unlike gasoline engines, only air is drawn into the cylinder during the intake stroke. This air is then compressed to very high pressures (typically 15:1 to 23:1 ratio), significantly raising its temperature.

Ignition and Expansion

Near the end of the compression stroke, diesel fuel is injected directly into the superheated air. The fuel atomizes and ignites spontaneously due to the high temperature. Combustion occurs at near-constant pressure initially, driving the piston down during the power stroke. The resulting exhaust gases are expelled during the exhaust stroke.

Thermodynamic Idealization

The ideal diesel cycle is often represented by a pV (pressure-volume) diagram. It illustrates compression, constant-pressure heat addition (combustion), adiabatic expansion, and constant-volume heat rejection (exhaust). The high compression ratio is key to both ignition and efficiency, avoiding the pre-ignition issues faced by spark-ignition engines.

Efficiency

Superior Fuel Economy

Diesel engines generally exhibit higher thermal efficiency than gasoline engines. This is primarily due to their high compression ratios, lean-burn operation (excess air), and the absence of throttling losses. Theoretical efficiencies can reach up to 75%, with practical efficiencies ranging from around 43% for passenger cars to over 55% for large marine engines.

Load Dependency

While peak efficiencies are impressive, the average efficiency in real-world driving cycles is lower. Diesel engines maintain better efficiency than gasoline engines at lower loads, but their overall performance is influenced by factors like engine speed, load, and auxiliary systems.

Factors Influencing Efficiency

Key elements contributing to diesel efficiency include: high compression ratios, lean air-fuel mixtures, direct fuel injection, turbocharging, and optimized combustion chamber design. Modern advancements continue to push these efficiency boundaries.

Emissions

Combustion Byproducts

As combustion engines, diesel engines produce exhaust gases including carbon monoxide, hydrocarbons, particulate matter (soot), and nitrogen oxides (NOx). Incomplete combustion is a primary cause of these emissions.

Control Technologies

Modern diesel engines employ sophisticated exhaust gas treatment systems, such as diesel particulate filters (DPFs) and selective catalytic reduction (SCR) systems, to significantly reduce harmful emissions. These technologies, coupled with advancements in fuel injection and engine management, help meet stringent environmental regulations.

Health Concerns

Diesel exhaust particulate matter is classified as a carcinogen and is linked to respiratory and cardiovascular diseases. Strict emission controls are mandated to protect public health.

Applications

Commercial Vehicles

The high torque, durability, and fuel efficiency of diesel engines make them ideal for trucks, buses, construction equipment, and agricultural machinery. Their robust design withstands demanding operational conditions.

Marine and Rail

Diesel engines are the primary power source for ships, from small vessels to massive cargo carriers, due to their reliability and fuel economy. They also power locomotives, providing the necessary torque for heavy hauling.

Power Generation

Diesel engines are widely used in stationary applications for electricity generation, serving as primary power sources in remote locations or as backup generators for critical facilities, ensuring reliable power supply.

Aviation

While historically less common in aviation, diesel engines have seen a resurgence, particularly for light aircraft and unmanned aerial vehicles, offering improved fuel efficiency and range compared to traditional piston engines.

Major Manufacturers

Global Leaders

The diesel engine industry features a diverse range of global manufacturers specializing in various engine types and applications. These companies drive innovation in performance, efficiency, and emissions control.

MTU Friedrichshafen (Germany)
MAN SE (Germany)
Wärtsilä (Finland)
Rolls-Royce Power Systems (Germany)
Siemens (Germany)
General Electric (USA)
Volvo Penta (Sweden)
Cummins (USA)
Mitsubishi Heavy Industries (Japan)
Caterpillar Energy Solutions (Germany)
EMD (Electro-Motive Diesel) (USA)
Fairbanks Morse (USA)

Fuel Characteristics

Fuel Properties

Diesel fuel is valued for its high energy density, good lubrication properties, and lower flammability compared to gasoline. Its high cetane number facilitates spontaneous ignition under compression, a critical factor for diesel engine operation.

Biodiesel and Alternatives

Biodiesel, derived from vegetable oils or animal fats, can be used in many diesel engines, offering a renewable alternative. The versatility of diesel engines allows them to operate on a range of fuels, including gas oils, kerosene, and even certain vegetable oils, provided viscosity and ignition properties are suitable.

Cold Weather Performance

A key challenge with diesel fuel is its tendency to gel or solidify in cold temperatures, potentially clogging fuel filters. Modern diesel fuels and additives, along with engine heating systems (glow plugs, flame-start), mitigate these issues, enabling operation in sub-zero conditions.

Safety Considerations

Flammability

Diesel fuel possesses a higher flash point than gasoline, making it less volatile and reducing the risk of ignition from sparks or static electricity. However, diesel vapors can form explosive mixtures under specific conditions, particularly in enclosed spaces.

Health Risks

Diesel exhaust emissions, particularly particulate matter, are classified as carcinogenic and are associated with increased risks of lung and bladder cancer, as well as respiratory and cardiovascular diseases. Strict emission controls are mandated to protect public health.

Engine Runaway

A critical safety concern is engine runaway, where the engine operates uncontrollably at excessive speeds. This can occur if the engine ingests flammable substances (like lubricating oil or fuel) that it then uses as fuel, bypassing the normal fuel control system.

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References

"IDI vs DI" Diesel hub

BMW AG (ed.): BMW E28 owner's manual, 1985, section 4â20

Wilkinson, Paul H.: "Diesel Aviation Engines," 1940, reproduced at Aviation Engine Historical Society, retrieved December 5, 2022

Karl H. Bergey: Assessment of New Technology for General Aviation Aircraft, Report for U.S. Department of Transportation, September 1978, p. 19

Rik D Meininger et al.: "Knock criteria for aviation diesel engines", International Journal of Engine Research, Vol 18, Issue 7, 2017, doi/10.1177

A full list of references for this article are available at the Diesel engine Wikipedia page

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Important Notice

This document has been generated by an AI and is intended for educational and informational purposes only. The content is derived from publicly available data and may not represent the most current or complete information available. It is crucial to consult official technical documentation and qualified engineering professionals for any practical application or detailed understanding.

This is not professional engineering advice. The information provided herein should not be used as a substitute for professional consultation, design, or analysis. Always seek the advice of a qualified mechanical engineer or relevant expert for specific requirements or concerns related to diesel engines.

The creators of this page are not responsible for any errors or omissions, or for any actions taken based on the information provided.

The Diesel Engine

💡 Dive in with Flashcard Learning! 💡

Introduction ℹ️

🔥 Compression Ignition

⚡ Efficiency and Power

🏭 Industrial Impact

History 📜

💡 Diesel's Vision

🚀 Early Development

⏳ Key Milestones

Operating Principle 💡

🔄 The Four-Stroke Cycle

🔥 Ignition and Expansion

📊 Thermodynamic Idealization

Efficiency ⚡

📈 Superior Fuel Economy

📉 Load Dependency

⚙️ Factors Influencing Efficiency

Emissions 💨

🏭 Combustion Byproducts

🔬 Control Technologies

⚠️ Health Concerns

Applications 🚗

🚚 Commercial Vehicles

🚢 Marine and Rail

💡 Power Generation

✈️ Aviation

Major Manufacturers 🏭

🌍 Global Leaders

Fuel Characteristics ⛽

💧 Fuel Properties

🌱 Biodiesel and Alternatives

❄️ Cold Weather Performance

Safety Considerations 🛡️

🔥 Flammability

⚠️ Health Risks

🚨 Engine Runaway

Teacher's Corner 🧑‍🏫

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References

📜 References

Feedback & Support 👍

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Disclaimer ⚠️

📜 Important Notice

Dive in with Flashcard Learning!

Introduction

Compression Ignition

Efficiency and Power

Industrial Impact

History

Diesel's Vision

Early Development

Key Milestones

Operating Principle

The Four-Stroke Cycle

Ignition and Expansion

Thermodynamic Idealization

Efficiency

Superior Fuel Economy

Load Dependency

Factors Influencing Efficiency

Emissions

Combustion Byproducts

Control Technologies

Health Concerns

Applications

Commercial Vehicles

Marine and Rail

Power Generation

Aviation

Major Manufacturers

Global Leaders

Fuel Characteristics

Fuel Properties

Biodiesel and Alternatives

Cold Weather Performance

Safety Considerations

Flammability

Health Risks

Engine Runaway

Teacher's Corner

True or False?

Test Your Knowledge!

Gamer's Corner

Discover other topics to study!

References

Feedback & Support

Disclaimer

Important Notice