Introduction to the Diesel Engine

Solar Energy International
Biodiesel Workshop

Diesel Vocabulary

• Aftercooling / Intercooling
• Turbocharging
• Cetane Number
• Cloud Point (CP)
• Flash Point
• Cold Filter Plugging Point (CFPP)
• Pour Point
• Compression Ignition (CI)
• Direct Injection (DI)
• In-Direct Injection (IDI)
• In-Line Injection Pump
• Nitrogen Oxides (NOx)
• Pump-Line-Nozzle Fuel System
• Rotary Injection Pump
• Unit Injector
• Common Rail Injection

What is a Diesel Engine?

• Rudolf Diesel developed the idea for the diesel engine and obtained the German patent for it in 1892.
• His goal was to create an engine with high efficiency.
• Gasoline engines had been invented in 1876 and, especially at that time, were not very
efficient
• Both the gasoline and diesel engine utilize the process of
internal combustion for power
What is Internal Combustion?

Four stroke cycle

• Intake stroke:

intake valve opens while the piston moves down from its highest position in the cylinder to its lowest position, drawing air into the cylinder in the process.

• Compression stroke:

intake valve closes and the piston moves back up the cylinder. This compresses the air & therefore heats it to a high temperature, typically in excess of 1000°F (540°C). Near the end of the compression stroke, fuel is injected into the cylinder. After a short delay, the fuel ignites spontaneously, a process called auto ignition.

• Combustion stroke:

The hot gases produced by the combustion of the fuel further increase the pressure in the cylinder, forcing the piston down

• Exhaust stroke:

exhaust valve opens when the piston is again near its lowest position, so that as the piston once more moves to its highest position, most of the burned gases are forced out of the cylinder.

Four stroke Cycle

Gasoline versus Diesel

• Spark ignition:
Gasoline engines use spark plugs to ignite fuel/ air mixture
• Compression ignition:
Diesel engines uses the heat of compressed air to ignite the fuel (intakes air, compresses it, then injects fuel)
• Fuel injection:
-Gasoline uses port fuel injection or carburetion;
-Diesel uses direct fuel injection or pre combustion chambers (indirect injection)
• Glow plugs:
-electrically heated wire that helps heat pre combustion chambers fuel when the engine is cold
- when a diesel engine is cold, compression may not raise air to temperature needed for fuel ignition

Compression Ratio

• Compression ratio:
This is defined as the ratio of the volume of the cylinder at the beginning of the compression stroke (when the piston is at BDC) to the volume of the cylinder at the end of the compression stroke (when the piston is at TDC).
• The higher the compression ratio, the higher the air temperature in the cylinder at the end of the compression stroke.
• Higher compression ratios, to a point, lead to higher thermal efficiencies and better fuel economies.
• Diesel engines need high compression ratios to generate the high temperatures required for fuel auto ignition.
• In contrast, gasoline engines use lower compression ratios in order to avoid fuel auto ignition, which manifests itself as engine knock or pinging sound.
• Common spark ignition compression ratio: 8:1 to 12:1
• Common compression ignition ration: 14:1 to 25:1

Direct Injection vs. Indirect
Injection

Direct Injection

• Direct-Injection (DI) or Open Chamber Engine: In this design, the fuel is injected directly into the cylinder chamber.

Direct injection engines have two design philosophies:
-High-swirl design, which have a deep bowl in the piston, a low number of holes in the injector and moderate injection pressures.
-Low-swirl or quiescent engines are characterized by having a shallow bowl in the piston, a large number of holes in the injector and higher injection pressures.
• Smaller engines tend to be of the high-swirl type, while bigger engines tend to be of the quiescent type
• All newer diesel engines use direct fuel injection
• Much higher fuel pressure then indirect fuel injection (example TDI )
• Injection/Injector Timing is critical
• Equipped with in-line pumps, distributor pumps, rail injection systems, or pump injector units

Indirect-Injection Engine (IDI)

In this design, the fuel is injected into a small pre-chamber attached to the main cylinder chamber.
The combination of rapidly swirling air in the prechamber and the jet-like expansion of combustion gases from the prechamber into the cylinder enhances the mixing and combustion
of the fuel and air.
Starting is aided by a high compression ratio (24-27) and a glow plug mounted in the pre-chamber.
This design has the advantage of less noise and faster combustion, but typically suffers from poorer fuel economy.

INTRODUCTION TO PIPING

Piping systems are like arteries and veins. They carry the lifeblood of modern civilization. In a modern city they transport water from the sources of water supply to the points of distribution; convey waste from residential and commercial buildings and other civic facilities to the treatment facility or the point of discharge. Similarly, pipelines carry crude oil from oil wells to tank farms for storage or to refineries for processing. The natural gas transportation and distribution lines convey natural gas from the source and storage tank forms to points of utilization, such as power plants, industrial facilities, and commercial and residential communities. In chemical plants, paper mills, food processing plants, and other similar industrial establishments, the piping systems are utilized to carry liquids, chemicals, mixtures, gases,
vapors, and solids from one location to another.

The fire protection piping networks in residential, commercial, industrial, and other buildings carry fire suppression fluids, such as water, gases, and chemicals to provide protection of life and property. The piping systems in thermal power plants convey high-pressure and high-temperature steam to generate electricity. Other piping systems in a power plant transport high- and low-pressure water, chemicals, low-pressure steam, and condensate. Sophisticated piping systems are used to process and carry hazardous and toxic substances. The storm and waste water piping systems transport large quantities of water away from towns, cities, and industrial and similar establishments to safeguard life, property, and essential facilities.

In health facilities, piping systems are used to transport gases and fluids for medical purposes. The piping systems in laboratories carry gases, chemicals, vapors, and other fluids that are critical for conducting research and development. In short, the piping systems are an essential and integral part of our modern civilization just as arteries and veins are essential to the human body.

The design, construction, operation, and maintenance of various piping systems involve understanding of piping fundamentals, materials, generic and specific design considerations, fabrication and installation, examinations, and testing and inspection requirements, in addition to the local, state and federal regulations.

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Heat Pipe



The heat pipe that rotates about its longitudinal or radial axes is called a rotating heat pipe. The rotating heat pipe is a very effective device for transmitting the heat at high rates within small temperature difference with a simple construction and an easy control. It has been employed in the cooling systems of the thermal turbine components, automobile brakes, the rotating metal cutting tools, and the electric machines. Therefore, alternative operating conditions for the rotating heat pipe, such as varying the rotational speed, varying the taper angle, and varying the input heat load, are presented and well investigated.

The main objective of this study is to compare the performance between two different taper angle heat pipes of 0° and 4°, by varying the remaining parameters on them both. The rotational speeds experimented were within the range from 300 to 700 [rev/min]. Different theoretical and experimental models of the rotating heat pipes are presented and comparisons between them are discussed. And finally this study gives a semi-comprehensive picture for the rotating heat pipes performance.













One limitation of the basic thermosyphon is that in order for the condensate to be returned to the evaporator region by gravitational force, the latter must be situated at the lowest point.
The basic heat pipe differs from the thermosyphon in that a wick, constructed for example from a few layers of fine gauze, is fixed to the inside surface and capillary forces return the condensate to the evaporator. (See Fig. 1.1b.) In the heat pipe the evaporator position is not restricted and it may be used in any orientation. If, of course, the heat pipe evaporator happens to be in the lowest position, gravitational forces will assist the capillary forces. The term ‘heat pipe’ is also used to describe high thermal conductance devices in which the condensate return is achieved by other means, for example centripetal force, osmosis or electrohydrodynamics.


Heat pipes and Capillary-driven two-phase systems offer significant advantages over traditional single-phase systems. With the typically increased thermal capacity associated with the phase change of a working fluid, considerably smaller mass flow rates are required to transport equivalent amounts than in single-phase liquid or gas systems for a given temperature range. Moreover, heat transfer coefficients of two phase systems are much greater than in single-phase flows and result in enhanced heat transfer. Lower mass flow rates and enhanced thermal characteristics provide the benefits of smaller system size (and weight) while providing increased performance.
The thermal capacity of a single-phase system depends on the temperature change of the working fluid; thus, a large temperature gradient or a high mass flow rate is required to transfer a large amount of heat. However, a two-phase system can provide essentially isothermal operation regardless of variations in the heat load. Additionally, single phase systems require the use of mechanical pumps and fans to circulate the working fluid, while capillary-driven two-phase systems have no external power requirements, which make such systems more reliable and free of vibration.








Theoretically, heat pipe operation is possible at any temperature between the triple state and the critical point of the working fluid utilized, albeit at significantly reduced transport capabilities near the two extremes due to the fluid property characteristics of surface tension and viscosity. Several typical heat pipe working fluids are given in Table 1.2, along with the corresponding triple point, critical point, and most widely utilized temperature range for each individual fluid. Classification of heat pipes may
be in terms of geometry , intended applications, or the type of working fluid utilized.

Each heat pipe application has a temperature range in which the heat pipe is intended to operate. Therefore, the working fluid must be chosen to take into account this operating temperature (along with the pressure condition), but also its chemical compatibility with the container and wick materials (see Table 1.3)

Depending on operating temperature, four different types of heat pipes are usually described with regard to commonly used working fluids:

1. Cryogenic heat pipes designed to operate from 1 to 200 K, with working fluids such as helium, argon, neon, nitrogen, and oxygen. These typically have relatively low heat transfer capabilities, due to very low values of the latent heat of vaporization, hfg, and low surface tensions of the working fluids. In addition, startup of the heat pipe involves transitioning from a supercritical state to an operating liquid–vapor condition.

2. Room (low)-temperature heat pipes with operating temperatures ranging between 200 and 550 K. Working fluids typically used in this range include methanol, ethanol, ammonia, acetone, and water.

3. Medium-temperature heat pipes with operating temperatures ranging from 550 to 700 K. Mercury and sulfur are typical fluids in this range, along with some organic fluids (e.g., naphthalene and biphenyl).

4. High (liquid-metal)-temperature heat pipes operating above 700 K. Very high heat fluxes can be obtained using liquid metals due to the characteristics of the fluid: namely, very large surface tensions and high latent heats of vaporization. Examples of liquid metals commonly used include potassium, sodium, and silver. In the case of liquid metal heat pipes, startup typically involves starting from an initially frozen working fluid.

1.2 Heat pipe thermodynamics:

Zuo and Faghri in 1998 presented a network thermodynamics analysis of the heat pipe that provided a unique into the heat pipe operation physics behind. This physics behind was considered a thermal network of various components. In addition, they described the transient heat pipe behavior with a first order linear ordinary differential equation and they described the working fluid undergoing a thermodynamic cycle.

One of the strongest opposing arguments was that the working fluid inside the heat pipe is seldom in an equilibrium state and consequently the working fluid cannot be specified on a T-s diagram. But Zuo and Faghri used the internal combustion engine (ICE) as an example to clarify their thermodynamics cycle approach. As background knowledge in the typical internal combustion cylinder, the fuel is mixed with air to undergo a four–process cycle of intake, compression, power and exhaust. Inside the cylinder is a mixture of air, water vapor hydrocarbons and other substances resulting from the combustion. Each cycle lasts approx. 0.01 sec for 5000 rev/min in two stroke engine. complete equilibrium is an impossible thing to reach in such a rapid cycle containing so many chemical components. However, the internal combustion cycle has been successfully analyzed on a T-s diagram in numerous textbooks.
Depending upon this example Zuo and Faghri provided a simplified engineering model for the heat pipe by representing a heat pipe working fluid circulation on T-s diagram as shown in Figure 1.3. Furthermore this model is able to use the thermodynamic cycle approach to analyze the heat pipe characteristics such as the condensation and evaporation process as well as the internal flow analysis. As the thermodynamic cycle is the heat pipe occurs at a much slower pace than in the internal combustion cycle, so the thermodynamic analysis in the heat pipe is more accurate than it is in the case of internal combustion engine ( ICE ).

1.3 Modes of heat transfer:
The thermal energy is transported through the heat pipe in two forms, transferring form and carrying form:
- The transferring form is the conventional heat transfer mechanisms through both the evaporator and the condenser sections that mainly depend upon the heat pipe geometric dimensions, the thermal properties of the heat pipe materials and the heat transfer coefficient of the heat source and the heat sink.