The diesel engine

The name diesel comes from the inventor of the diesel engine, R. Diesel. There are both four- and two-stroke-cycle diesel engines. Most  automotive diesels are four-stroke engines. The intake stroke on the diesel engine draws only air into the cylinder. The air is then compressed during the compression stroke. At near maximum compression, finely atomized diesel fuel (a gas oil having a high flashpoint) is sprayed into the hot air, initiating auto ignition of the mixture. During the subsequent power stroke, the expanding hot mixture works on the piston, then burnt gases are purged during the exhaust stroke.
Since diesel engines do not use a spark plug, they are also referred to as compression ignition (CI) engines. In the case of petrol engines, too high a temperature in the combustion chamber ignites the petrol spontaneously.
When this occurs, the plug cannot control the moment of ignition. This unwanted phenomenon is often referred to as ‘knocking’.
The diesel is an injection engine. A petrol engine normally needs a throttle valve to control airflow into the cylinder, but a diesel engine does not. Instead, the diesel uses a fuel injection pump and an injector nozzle sprays fuel right into the combustion chamber at high pressure. The amount of fuel injected into the cylinder controls the engine power and speed. There are two methods3 by which fuel is injected into a combustion chamber, direct or indirect injection.
With direct injection engines (DI) the fuel is injected directly into the cylinder and initial combustion takes place within the bowl that is machined into the piston head itself. With indirect injection engines (IDI) the fuel is injected and initial combustion takes place in a small pre-combustion chamber formed in the cylinder head. The burning gases then expand into the cylinder where combustion continues. Pistons for IDI engines usually have shallow depressions in their heads to assist the combustion process. Although an IDI engine has
some advantages, it cannot match the efficiency of a DI engine, which is why most new automotive diesel engines entering production are DI designs.
Turbo charged engines are mainly used because diesels can generate only a low power output without turbocharging. Turbocharging with an intercooler is used in large engines. Diesel engines produce lean combustion, having an air-fuel ratio of about 15:1 up to 100:1. The diesel’s leaner fuel mixture generates higher fuel economy compared to that of a petrol engine. The peak cylinder pressure can be in excess of 15 MPa. The HC and CO contents in the exhaust gas are lower compared to those of petrol engines, but the particulate soot and NOx emissions cause environmental problems. In comparison with  petrol engines, the components in a diesel engine are exposed to significantly more arduous operating conditions. Up until the 1980s, the noise, exhaust smoke and poor performance of diesel engines made them less attractive.
However, recently improved diesel engines with high torque now offer a more attractive alternative to petrol engines. A Stirling engine is another type of engine that uses a piston-cylinder construction. There are, however, other engines, such as the rotary and gas turbine engines, that do not use the piston-cylinder mechanism.





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  • The science and technology of materials in automotive engines
    Hiroshi Yamagata
    Woodhead Publishing and Maney Publishing
    on behalf of
    The Institute of Materials, Minerals & Mining
    CRC Press
    Boca Raton Boston New York Washington, DC
    WOODHEAD PUBLISHING LIMITED
    Cambridge England




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  • Valve operation

    Function
    The two main types of internal combustion engine are: spark ignition (SI) engines (petrol, gasoline, or gas engines), where the fuel ignition is caused by a spark; and compression ignition (CI) engines (diesel engines), where the rise in pressure and temperature is high enough to ignite the fuel. Valves are used in these engines to control the induction and exhaust processes.

    Both types of engine can be designed to operate in either two strokes of the piston or four strokes of the piston. The four-stroke operating cycle can be explained by reference to Fig. 2.1. This details the position of the piston and valves during each of the four strokes.
    1. The induction stroke The inlet valve is open. The piston moves down the cylinder drawing in a charge of air.
    2. The compression stroke Inlet and exhaust valves are closed. The piston moves up the cylinder. As the piston approaches the top of the cylinder (top dead centre – tdc) ignition occurs. In engines utilizing direct injection (DI) the fuel is injected towards the end of the stroke.
    3. The expansion stroke Combustion occurs causing a pressure and temperature rise which pushes the piston down. At the end of the stroke the exhaust valve opens.
    4. The exhaust stroke The exhaust valve is still open. The piston moves up forcing exhaust gases out of the cylinder.



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  • N G I N E E R I N G R E S E A R C H S E R I E S
    Automotive Engine Valve Recession
    R Lewis and R S Dwyer-Joyce
    Series Editor
    Duncan Dowson
    Professional Engineering Publishing Limited,
    London and Bury St Edmunds, UK



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  • The two-stroke engine

    The two-stroke engine is similar to that of the four-stroke-cycle engine in its reciprocating mechanism. It uses the piston-crankshaft mechanism, but requires
    only one revolution of the crankshaft for a complete power-producing cycle.
    The two-stroke engine does not use inlet and exhaust valves. The gas exchange
    is implemented by scavenging and exhaust porthole openings in the bore wall. The upward and downward motion of the piston simultaneously opens and closes these portholes. The air-fuel mixture then goes in or out of the combustion chamber through the portholes. Combustion takes place at every rotation of the crankshaft.

    In the two-stroke engine, the space in the crankcase works as a precompression chamber for each successive fuel charge. The fuel and lubricating oil are premixed and introduced into the crankcase, so that the crankcase
    cannot be used for storing the lubricating oil. When combustion occurs in the cylinder, the combustion pressure compresses the new gas in the crankcase for the next combustion. The burnt gas then exhausts while drawing in new gas. The lubricating oil mixed into the air-fuel mixture also burns.

    Since the two-stroke engine does not use a valve system, its mechanism is very simple. The power output is fairly high because it achieves one power stroke per two revolutions of the crankshaft. However, although the power output is high, it is used only for small motorcycle engines and some large diesel applications. Since the new gas pushes out the burnt gas, the intake and exhaust gases are not clearly separated. As a result, fuel consumption is relatively high and cleaning of the exhaust gas by a catalytic converter is difficult.

    In the past, petrol engines almost universally used3 a carburetor. However, the requirements for improved fuel economy have led to an increasing use of fuel injection. In a petrol engine the fuel is normally injected into the inlet manifold behind the inlet valve. The atomized fuel mixes with air. When the inlet valve is opened, the combustible mixture is drawn into the cylinder. 

    However, a recent development has occurred in direct injection petrol engines whereby fuel is injected directly into the combustion chamber, as with direct injection diesel engines.



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  • The science and technology of materials in automotive engines
    Hiroshi Yamagata
    Woodhead Publishing and Maney Publishing
    on behalf of
    The Institute of Materials, Minerals & Mining
    CRC Press
    Boca Raton Boston New York Washington, DC
    WOODHEAD PUBLISHING LIMITED
    Cambridge England


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    www.automotive-technology-guide.com

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  • Fuel Cell Vehicles

    Fuel cells are electrochemical devices that turn hydrogen directly into electricity without combustion, at high efficiency and with emissions only of water. For a fuel cell-powered vehicle, the hydrogen can either be carried onboard or produced from a hydrogen-rich fuel such as methanol. 50 Although there are several types of fuel cells, most analysts consider the proton exchange membrane (PEM) fuel cell as the best candidate for vehicle applications, because of its low-temperature operation and expected potential to achieve high power density and low cost.


    Achieving low cost and small size and weight remains a substantial development challenge, however. Current fuel cells cost thousands of dollars per kW and are too large to fit comfortably in a light-duty vehicle; researchers hope to reduce their costs to less than $40/kW and shrink their size to fit into a car without usurping its cargo space. In fact, recent fuel cell prototypes have demonstrated substantial success in size reduction.

    While longer term prospects show promise, OTA considers it unlikely that a PEM fuel cell can be successfully commercialized for high-volume, light-duty vehicle applications by 2005, although fuel cell developers are hoping for early commercialization in larger vehicle applications (buses, locomotives); 2015, or perhaps a bit before, seems a more likely date for commercialization, if the many remaining development challenges are successfully met. By that year, an aluminum-bodied mid-size PEM fuel cell vehicle with methanol fuel and a bipolar lead acid battery for high power needs and cold start power might be capable of achieving about 80 mpg.51 The price of such a vehicle is extremely uncertain. With current fuel cell designs, assuming that  substantial cost reductions from current values are achieved and the designs are optimized and produced in large quantities, a mid-size car could cost $40,000 more than an equivalent baseline car. If fuel cell
    developers can cut costs to $65/kW or below for both fuel cell and reformer, the incremental price could be $6,000 or less. The incremental vehicle price could also be reduced substantially by relaxing the maximum continuous power requirement, thus allowing a smaller fuel cell to be used.52 This conceivably might be a reasonable tradeoff for an urban commuter vehicle, but not for an all-purpose vehicle.

    Small vehicular fuel cells are still at a relatively early stage of development, and system improvements have come rapidly. Successful commercialization, however, will depend on great improvements in a host of separate development areas—size and cost reduction of methanol reformers, development of low-cost, high-energy-density, onboard hydrogen storage; shrinkage of fuel cell “balance of plant”; reduction of platinum catalyst requirements53; and a good many others. Differing degrees of optimism about the likely success of these R&D efforts explain most of the differences among the various estimates of future fuel cell performance and cost. In OTA’s view, the most optimistic estimates, such as fuel cell costs at well below $65/kW, are certainly possible but require a substantial degree of good fortune in the R&D effort-and the progress
    needed is unlikely to come quickly. 



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  • Advanced Automotive Technology: Visions
    of a Super-Efficient Family Car
    OTA-ETI-638
    GPO stock #052-003-01440-8



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  • How to Know the clutch plates are depleted shelf life.

    Use the clutch on the vehicle can not be predicted when its use.Because it depends on vehicle usage and driver behavior. However, it must gradually be eroded  thin-plate clutch. Symptoms felt the pull of the car becomes sluggish or not powered, although the gas in the hitch.
    In cars with automatic transmission, signs of wear and tear on the clutch plates when the car is on the road, the position of the gears do not shift, even though high-rev engine.
    While in a car with manual transmission, how to know the signs of the wear plate clutch is turned on the machine without running the car and put the gear lever in first gear position. Then pull the emergency brake and stepped on the brake pedal. Then, remove the stamping on the left foot on the clutch pedal slowly while pressing the brake pedal. Well, if you rev the engine stopped, it means that the clutch plates are still good and worthy life. But if the opposite happens, the clutch plates should be quickly replaced.


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