Sorine cu parere de rau trebuie sa ti spun ca esti intr-o eroare maxima cu tinutul asta una si buna ca dieselul nu e bun ca e mort etc etc !!....Vad ca geaba am dat lincuri utile tot o tii pe a ta...Uite mai jos o sa-i zicem analiza a motorului Diesel, poate o sa intelegi ca totusi motoarele Diesel nu vor muri mai repede decat cele pe benzina...Eu nu stiu tie chiar nu ti da de gandit ca toti marii producatori de auto (unii cu o traditie in motoare MAS au trecut la fabricarea unor motoare Diesel!!?!Chiar nu vezi asta!?!
Advantages and disadvantages versus spark-ignition engines
[edit] Power and fuel economy
Diesel engines are more efficient than gasoline (petrol) engines of the same power, resulting in lower fuel consumption. A common margin is 40% more miles per gallon for an efficient turbodiesel. For example, the current model Škoda Octavia, using Volkswagen Group engines, has a combined Euro rating of 38 miles per US gallon (6.2 L/100 km) for the 102 bhp (76 kW) petrol engine and 54 mpg (4.4 L/100 km) for the 105 bhp (75 kilowatts) diesel engine. However, such a comparison doesn't take into account that diesel fuel is denser and contains about 15% more energy by volume. Although the calorific value of the fuel is slightly lower at 45.3 MJ/kg (megajoules per kilogram) than gasoline at 45.8 MJ/kg, liquid diesel fuel is significantly denser than liquid gasoline. When this is taken into account, diesel fuel has a higher energy density than petrol; this volumetric measure is the main concern of many people, as diesel fuel is sold by volume, not weight, and must be transported and stored in tanks of fixed size.
Adjusting the numbers to account for the energy density of diesel fuel, one finds the overall energy efficiency of the aforementioned paragraph is still about 20% greater for the diesel version, despite the weight penalty of the diesel engine. When comparing engines of relatively low power for the vehicle's weight (such as the 75 hp VW Golf), the diesel's overall energy efficiency advantage is reduced further but still between 10 and 15 percent.
While higher compression ratio is helpful in raising efficiency, diesel engines are much more economical than gasoline (petrol) engines when at low power and at engine idle. Unlike the petrol engine, diesels lack a butterfly valve (throttle) in the inlet system, which closes at idle. This creates parasitic drag on the incoming air, reducing the efficiency of petrol/gasoline engines at idle. Due to their lower heat losses, diesel engines have a lower risk of gradually overheating if left idling for long periods of time. In many applications, such as marine, agriculture, and railways, diesels are left idling unattended for many hours or sometimes days. These advantages are especially attractive in locomotives (see dieselization).
Naturally aspirated diesel engines are heavier than gasoline engines of the same power for two reasons. The first is that it takes a larger displacement diesel engine to produce the same power as a gasoline engine. This is essentially because the diesel must operate at lower engine speeds.[4] Diesel fuel is injected just before ignition, leaving the fuel little time to reach all the oxygen in the cylinder. In the gasoline engine, air and fuel are mixed for the entire compression stroke, ensuring complete mixing even at higher engine speeds. The second reason for the greater weight of a diesel engine is it must be stronger to withstand the higher combustion pressures needed for ignition, and the shock loading from the detonation of the ignition mixture. As a result, the reciprocating mass (the piston and connecting rod), and the resultant forces to accelerate and to decelerate these masses, are substantially higher the heavier, the bigger and the stronger the part, and the laws of diminishing returns of component strength, mass of component and inertia — all come into play to create a balance of offsets, of optimal mean power output, weight and durability.
Yet it is this same build quality that has allowed some enthusiasts to acquire significant power increases with turbocharged engines through fairly simple and inexpensive modifications. A gasoline engine of similar size cannot put out a comparable power increase without extensive alterations because the stock components would not be able to withstand the higher stresses placed upon them. Since a diesel engine is already built to withstand higher levels of stress, it makes an ideal candidate for performance tuning with little expense. However, it should be said that any modification that raises the amount of fuel and air put through a diesel engine will increase its operating temperature which will reduce its life and increase its service interval requirements. These are issues with newer, lighter, high performance diesel engines which aren't "overbuilt" to the degree of older engines and are being pushed to provide greater power in smaller engines.
The addition of a turbocharger or supercharger to the engine greatly assists in increasing fuel economy and power output, mitigating the fuel-air intake speed limit mentioned above for a given engine displacement. Boost pressures can be higher on diesels than gasoline engines, due to the latter's susceptibility to knock, and the higher compression ratio allows a diesel engine to be more efficient than a comparable spark ignition engine. Because the burned gases are expanded further in a diesel engine cylinder, the exhaust gas is cooler, meaning turbochargers require less cooling, and can be more reliable, than on spark-ignition engines.
The increased fuel economy of the diesel engine over the gasoline engine means that the diesel produces less carbon dioxide (CO2) per unit distance. Recently, advances in production and changes in the political climate have increased the availability and awareness of biodiesel, an alternative to petroleum-derived diesel fuel with a much lower net-sum emission of CO2, due to the absorption of CO2 by plants used to produce the fuel.
The two main factors that held diesel engine back in private vehicles until quite recently were their low power outputs and high noise levels (characterised by knock or clatter, especially at low speeds and when cold). This noise was caused by the sudden ignition of the diesel fuel when injected into the combustion chamber. This noise was a product of the sudden temperature change, hence it was more pronounced at low engine temperatures. A combination of improved mechanical technology (such as two-stage injectors which fire a short 'pilot charge' of fuel into the cylinder to warm the combustion chamber before delivering the main fuel charge) and electronic control (which can adjust the timing and length of the injection process to optimise it for all speeds and temperatures) have partially mitigated these problems in the latest generation of common-rail designs. Poor power and narrow torque bands have been helped by the use of turbochargers and intercoolers.
[edit] Emissions
Diesel engines produce very little carbon monoxide as they burn the fuel in excess air even at full load, at which point the quantity of fuel injected per cycle is still about 50% lean of stoichiometric. However, they can produce black soot (or more specifically diesel particulate matter) from their exhaust, which consists of unburned carbon compounds. This is often caused by worn injectors, which do not atomize the fuel sufficiently, or a faulty engine management system which allows more fuel to be injected than can be burned completely in the available time.
The full load limit of a diesel engine in normal service is defined by the "black smoke limit", beyond which point the fuel cannot be completely combusted; as the "black smoke limit" is still considerably lean of stoichiometric it is possible to obtain more power by exceeding it, but the resultant inefficient combustion means that the extra power comes at the price of reduced combustion efficiency, high fuel consumption and dense clouds of smoke, so this is only done in specialised applications (such as tractor pulling) where these disadvantages are of little concern.
Likewise, when starting from cold, the engine's combustion efficiency is reduced because the cold engine block draws heat out of the cylinder in the compression stroke. The result is that fuel is not combusted fully, resulting in blue/white smoke and lower power outputs until the engine has warmed through. This is especially the case with in-direct injection engines which are less thermally efficient. With electronic injection, the timing and length of the injection sequence can be altered to compensate for this. Older engines with mechanical injection can have manual control to alter the timing, or multi-phase electronically-controlled glow plugs, that stay on for a period after start-up to ensure clean combustion- the plugs are automatically switched to a lower power to prevent them burning out.
Particles of the size normally called PM10 (particles of 10 micrometres or smaller) have been implicated in health problems, especially in cities. Some modern diesel engines feature diesel particulate filters, which catch the black soot and when saturated are automatically regenerated by burning the particles. Other problems associated with the exhaust gases (nitrogen oxides, sulfur oxides) can be mitigated with further investment and equipment; some diesel cars now have catalytic converters in the exhaust.
[edit] Power and torque
For commercial uses requiring towing, load carrying and other tractive tasks, diesel engines tend to have more desirable torque characteristics. Diesel engines tend to have their torque peak quite low in their speed range (usually between 1600–2000 rpm for a small-capacity unit, lower for a larger engine used in a truck). This provides smoother control over heavy loads when starting from rest, and crucially allows the diesel engine to be given higher loads at low speeds than a petrol engine, which makes them much more economical for these applications. This characteristic is not so desirable in private cars, so most modern diesels used in such vehicles use electronic control, variable geometry turbochargers and shorter piston strokes to achieve a wider spread of torque over the engine's speed range, typically peaking at around 2500–3000 rpm.
[edit] Reliability
The lack of an electrical ignition system greatly improves the reliability. The high durability of a diesel engine is also due to its overbuilt nature (see above) as well as the diesel's combustion cycle, which creates less-violent changes in pressure when compared to a spark-ignition engine, a benefit that is magnified by the lower rotating speeds in diesels. Diesel fuel is a better lubricant than gasoline so is less harmful to the oil film on piston rings and cylinder bores; it is routine for diesel engines to cover 250,000 miles (400 000 km) or more without a rebuild.
Unfortunately, due to the greater compression force required and the increased weight of the stronger components, starting a diesel engine is a harder task. More torque is required to push the engine through compression.
Either an electrical starter or an air start system is used to start the engine turning. On large engines, pre-lubrication and slow turning of an engine, as well as heating, are required to minimize the amount of engine damage during initial start-up and running. Some smaller military diesels can be started with an explosive cartridge, called a Coffman starter, which provides the extra power required to get the machine turning. In the past, Caterpillar and John Deere used a small gasoline pony motor in their tractors to start the primary diesel motor. The pony motor heated the diesel to aid in ignition and utilized a small clutch and transmission to actually spin up the diesel engine. Even more unusual was an International Harvester design in which the diesel motor had its own carburetor and ignition system, and started on gasoline. Once warmed up, the operator moved two levers to switch the motor to diesel operation, and work could begin. These engines had very complex cylinder heads (with their own gasoline combustion chambers) and in general were vulnerable to expensive damage if special care was not taken (especially in letting the engine cool before turning it off).
As mentioned above, diesel engines tend to have more torque at lower engine speeds than gasoline engines. However, diesel engines tend to have a narrower power band than gasoline engines. Naturally-aspirated diesels tend to lack power and torque at the top of their speed range. This narrow band is a reason why a vehicle such as a truck may have a gearbox with as many as 16 or more gears, to allow the engine's power to be used effectively at all speeds. Turbochargers tend to improve power at high engine speeds, superchargers do the same at lower speeds, and variable geometry turbochargers improve the engine's performance equally (or make the torque curve flatter).
[edit] Quality and variety of fuels
Petrol/gasoline engines are limited in the variety and quality of the fuels they can burn. Older petrol engines fitted with a carburetor required a volatile fuel that would vaporize easily to create the necessary fuel/air mix for combustion. Because both air and fuel are admitted to the cylinder, if the compression ratio of the engine is too high or the fuel too volatile (with too low an octane rating), the fuel will ignite under compression, as in a diesel engine, before the piston reaches the top of its stroke. This pre-ignition causes a power loss and over time major damage to the piston and cylinder. The need for a fuel that is volatile enough to vaporize but not too volatile (to avoid pre-ignition) means that petrol engines will only run on a narrow range of fuels. There has been some success at dual-fuel engines that use gasoline/Ethanol, gasoline/Propane, and gasoline/Methane.
In diesel engines, a mechanical injector system vaporizes the fuel (instead of a Venturi jet in a carburetor as in a petrol engine). This forced vaporisation means that less volatile fuels can be used. More crucially, because only air is inducted into the cylinder in a diesel engine, the compression ratio can be much higher as there is no risk of pre-ignition provided the injection process is accurately timed. This means that cylinder temperatures are much higher in a diesel engine than a petrol engine allowing less combustible fuels to be used.
Diesel fuel is a form of light fuel oil, very similar to kerosene, but diesel engines, especially older or simple designs that lack precision electronic injection systems, can run on a wide variety of other fuels. One of the most common alternatives is vegetable oil from a very wide variety of plants. Some engines can be run on vegetable oil without modification, and most others require fairly basic alterations. Bio-diesel is a pure diesel-like fuel refined from vegetable oil and can be used in nearly all diesel engines. The only limits on the fuels used in diesel engines are the ability of the fuel to flow along the fuel lines and the ability of the fuel to lubricate the injector pump and injectors adequately.
Most large marine diesels (often called cathedral engines due to their size) run on heavy fuel oil (sometimes called "bunker oil"), which is a thick, viscous and almost un-flammable fuel which is very safe to store and cheap to buy in bulk as it is a waste product from the petroleum refining industry. The fuel must be heated to thin it out (often by the exhaust header) and is often passed through multiple injection stages to vaporize it.
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Ia stai ca te contrazic si pe tine ca bag seama ca si tu ai cam ramas in urma... Pai adica Honda civic 2,2 D e cu o secunda "mai sport" ca OZN lui Satori, Audi castiga cursa dupa cursa cu motor Diesel si tu mai zici ca nu sunt sportive!?!..BMW de asemenea pune la greu Diesel pe masini si doar n-o sa te apuci sa spui unui BMW ca i tractor nu!?!?...Ca sa nu mai vorbim de consumurile astora ...
Ah si sa nu uit sa stii ca si GPL-ul tot de petrol depinde sau ai impresia ca vine din aer...
