Misplaced Pages

#406593

64-462: Two separate throttle bodies are used, each incorporating two throttle butterfly plates. This version was only sold in Portugal and Italy. It has a displacement reduced to 1,990 cc (121.4 cu in) by shortening the stroke to 72.6 mm (2.9 in). Applications: The E30 M3 was initially released with the 147 kW (197 bhp) S14B23 engine. Versions equipped with

128-664: A catalytic converter produced 143 kW (192 bhp) and 230 Nm. In April 1989, the Ravaglia and Cecotto limited edition M3s were released with a 158 kW (212 bhp) S14B23 that would in September, 1989 become the standard motor for the E30 M3. Applications: This update of the S14B23 produced 162 kW (217 bhp), or 158 kW (212 bhp) if equipped with a catalytic converter. Applications: In 1989,

192-429: A poppet valve , or series of poppet valves which open in sequence to regulate the amount of steam admitted to the steam chests over the pistons. It is used in conjunction with the reversing lever to start, stop and to control the locomotive's power although, during steady-state running of most locomotives, it is preferable to leave the throttle wide open and to control the power by varying the steam cut-off point (which

256-404: A butterfly valve in the intake tract. An exception to this generalization is newer diesel engines meeting stricter emissions standards, where such a valve is used to generate intake manifold vacuum, thereby allowing the introduction of exhaust gas (see EGR ) to lower combustion temperatures and thereby minimize NOx production. In a reciprocating engine aircraft, the throttle control is usually

320-408: A certain injector stay open and therefore how much fuel should be injected by each injection pulse. However, they do still need a throttle to control the airflow into the engine, together with a sensor that detects its current opening angle, so that the correct air/fuel ratio can be met at any RPM and engine load combination. The simplest way to do this is to simply remove the carburetor unit, and bolt

384-558: A cold engine. Moreover, the EGR valve was controlled, in part, by vacuum drawn from the carburetor's venturi, which allowed more precise constraint of EGR flow to only those engine load conditions under which NO x is likely to form. Later, backpressure transducers were added to the EGR valve control to further tailor EGR flow to engine load conditions. Most modern engines now need exhaust gas recirculation to meet NO x emissions standards. However, recent innovations have led to

448-465: A diesel reduces the specific heat ratio of the combustion gases in the power stroke . This reduces the amount of power that can be extracted by the piston, thereby reducing the thermodynamic efficiency. EGR also tends to reduce the completeness of fuel combustion during the power stroke. This is plainly evident by the increase in particulate emissions that corresponds to an increase in EGR. Particulate matter (mainly carbon and also known as soot) that

512-401: A hand-operated lever or knob. It controls the engine power output, which may or may not reflect in a change of RPM, depending on the propeller installation (fixed-pitch or constant speed ). Some modern internal combustion engines do not use a traditional throttle, instead relying on their variable intake valve timing system to regulate the airflow into the cylinders, although the result is

576-448: A mixture of nitrogen and oxygen is subjected to high temperature, the lower combustion chamber temperatures caused by EGR reduces the amount of NO x that the combustion process generates. Gases re-introduced from EGR systems will also contain near equilibrium concentrations of NO x and CO; the small fraction initially within the combustion chamber inhibits the total net production of these and other pollutants when sampled on

640-494: A reduction in fuel efficiency due to the back pressure created. Diesel particulate filters come with their own set of very specific operational and maintenance requirements. Firstly, as the DPF captures the soot particles (which are made far more numerous due to the use of EGR), the DPF itself progressively becomes loaded with soot. This soot must then be burned off, either actively or passively. At sufficiently high temperatures,

704-510: A simple unit containing a throttle body and fuel injectors on instead. This is known as single-port injection , also known by different marketing names (such as "throttle-body injection" by General Motors and "central fuel injection" by Ford , among others), and it allows an older engine design to be converted from carburetor to fuel injection without significantly altering the intake manifold design. More complex later designs use intake manifolds, and even cylinder heads , specially designed for

SECTION 10

#1732791708407

768-625: A single main stage (such as the Space Shuttle ), than for launch with multistage rockets . They are also useful in situations where the airspeed of the vehicle must be limited due to aerodynamic stress in the denser atmosphere at lower levels (e.g. the Space Shuttle). Rockets characteristically become lighter the longer they burn, with the changing ratio of thrust:weight resulting in increasing acceleration, so engines are often throttled (or switched off) to limit acceleration forces towards

832-447: A single oval or rectangular throttle plate, and works similarly to a single venturi carburetor, but with two small openings instead of one. A 4-venturi carburetor has two pairs of venturis, each pair regulated by a single oval or rectangular throttle plate. Under normal operation, only one throttle plate (the "primary") opens when the accelerator pedal is pressed, allowing more air into the engine, but keeping overall airflow velocity through

896-586: A single small throttle plate over a basic carburetor with a single venturi . The throttle is either open or closed (although there is always a small hole or other bypass to allow a small amount of air to flow through so the engine can idle when the throttle is closed), or some intermediate position. Since air velocity is crucial to the functioning of a carburetor, to keep average air velocity up, larger engines require more complex carburetors with multiple small venturis, typically two or four (these venturis are commonly called "barrels"). A typical "2-barrel" carburetor uses

960-444: A spark-ignition engine, an ancillary benefit of recirculating exhaust gases via an external EGR valve is an increase in efficiency, as charge dilution allows a larger throttle position and reduces associated pumping losses. Mazda's turbocharged SkyActiv gasoline direct injection engine uses recirculated and cooled exhaust gases to reduce combustion chamber temperatures, thereby permitting the engine to run at higher boost levels before

1024-528: A time average. Chemical properties of different fuels limit how much EGR may be used. For example methanol is more tolerant to EGR than gasoline. The first EGR systems were crude; some were as simple as an orifice jet between the exhaust and intake tracts which admitted exhaust to the intake tract whenever the engine was running. Difficult starting, rough idling, reduced performance and lost fuel economy inevitably resulted. By 1973, an EGR valve controlled by manifold vacuum opened or closed to admit exhaust to

1088-488: A typical automotive spark-ignited (SI) engine, 5% to 15% of the exhaust gas is routed back to the intake as EGR. The maximum quantity is limited by the need of the mixture to sustain a continuous flame front during the combustion event; excessive EGR in poorly set up applications can cause misfires and partial burns. Although EGR does measurably slow combustion, this can largely be compensated for by advancing spark timing. The impact of EGR on engine efficiency largely depends on

1152-459: Is a reduction in engine longevity. For example, because the EGR system routes exhaust gas directly back into the cylinder intake without any form of filtration, this exhaust gas contains carbon particulates . And, because these tiny particles are abrasive, the recirculation of this material back into the cylinder increases engine wear. This is so because these carbon particles will blow by the piston rings (causing piston-cylinder-interface wear in

1216-420: Is also omitted at idle (low-speed, zero load) because it would cause unstable combustion, resulting in rough idle. Since the EGR system recirculates a portion of exhaust gases, over time the valve can become clogged with carbon deposits, which will prevent it from operating properly. Clogged EGR valves can sometimes be cleaned, but replacement is necessary if the valve is faulty. Because diesel engines depend on

1280-431: Is done with the reversing lever), as this is more efficient. A steam locomotive throttle valve poses a difficult design challenge as it must be opened and closed using hand effort against the considerable pressure (typically 250 psi or 1,700 kPa) of boiler steam. One of the primary reasons for later multiple-sequential valves: it is far easier to open a small poppet valve against the pressure differential, and open

1344-494: Is effectively countered by the DPF, which collects these and in the end will burn those unburnt particles during regeneration, converting them into CO2 and water vapour emissions, that - unlike NOx gases - have no negative health effects. Modern cooled EGR systems help reduce engine wear by using the waste heat recouped from the recirculated gases to help warm the coolant and hence the engine block faster to operating temperature. This also helps lower fuel consumption through reducing

SECTION 20

#1732791708407

1408-439: Is found in the carburetor. When a throttle is wide open , the intake manifold is usually at ambient atmospheric pressure. When the throttle is partially closed, a manifold vacuum develops as the intake drops below ambient pressure. The power output of a diesel engine is controlled by regulating the quantity of fuel that is injected into the cylinder. Because diesel engines do not need to control air volumes, they usually lack

1472-467: Is mechanically connected to the throttle linkages, which, in turn, rotate the throttle plate. In cars with electronic throttle control (also known as "drive-by-wire"), an electric actuator controls the throttle linkages and the accelerator pedal connects not to the throttle body, but to a sensor, which outputs a signal proportional to the current pedal position and sends it to the ECU . The ECU then determines

1536-515: Is necessary to clean it up. The malfunction of the throttle could be indicated by illuminated EPC warning light. This is usually the case with modern Volkswagen Group vehicles. Vehicles not equipped with the EPC warning light indicate issues with the throttle by illuminated check engine symbol. Symptoms of the throttle malfunction could vary from poor idle, decreased engine power, poor mileage, bad acceleration , and so on. The effective way to increase

1600-438: Is not burned in the power stroke represents wasted energy. Because of stricter regulations on particulate matter (PM), the soot-increasing effect of EGR required the introduction of further emission controls in order to compensate for the resulting PM emission increases. The most common soot-control device is a diesel particulate filter (DPF) installed downstream of the engine in the exhaust system. This captures soot but causes

1664-430: Is of priority. A throttle body is somewhat analogous to the carburetor in a non-injected engine, although it is important to remember that a throttle body is not the same thing as a throttle , and that carbureted engines have throttles as well. A throttle body simply supplies a convenient place to mount a throttle in the absence of a carburetor venturi. Carburetors are an older technology, which mechanically modulate

1728-414: The engine idle to make a cold engine warm up faster or to account for eventual additional engine loads such as running air conditioning compressors in order to avoid engine stalls. The throttle on a gasoline engine is typically a butterfly valve . In a fuel-injected engine, the throttle valve is placed on the entrance of the intake manifold , or housed in the throttle body . In a carbureted engine, it

1792-463: The DPF by burning diesel fuel directly in the oxidation catalyst in order to significantly increase exhaust-gas temperatures through the DPF to the point where PM is incinerated by the residual oxygen in the exhaust. Because diesel fuel and engine oil both contain nonburnable (i.e. metallic and mineral) impurities, the incineration of soot (PM) in the DPF leaves behind a residue known as ash. For this reason, after repeated regeneration events, eventually

1856-547: The DPF must either be physically removed and cleaned in a special external process, or it must be replaced. As noted earlier, the feeding of the low-oxygen exhaust gas into the diesel engine's air intake engenders lower combustion temperatures, thereby reducing emissions of NO x . By replacing some of the fresh air intake with inert gases EGR also allows the engine to reduce the amount of injected fuel without compromising ideal air-fuel mixture ratio, therefore reducing fuel consumption in low engine load situation (for ex. while

1920-493: The ECU. The ECU then increases the amount of fuel injected by the injectors in order to obtain the required air-fuel ratio . Often a throttle position sensor (TPS) is connected to the shaft of the throttle plate to provide the ECU with information on whether the throttle is in the idle position, wide-open throttle (WOT) position, or somewhere in between these extremes. Throttle bodies may also contain valves and adjustments to control

1984-427: The air-fuel mixture must be enriched to prevent engine knocking . In a gasoline engine, this inert exhaust displaces some amount of combustible charge in the cylinder, effectively reducing the quantity of charge available for combustion without affecting the air-fuel ratio. In a diesel engine, the exhaust gas replaces some of the excess oxygen in the pre-combustion mixture. Because NO x forms primarily when

BMW S14 - Misplaced Pages Continue

2048-425: The amount of air flow (with an internal throttle plate) and combine air and fuel together ( venturi ). Cars with fuel injection don't need a mechanical device to meter the fuel flow, since that duty is taken over by injectors in the intake pathways (for multipoint fuel injection systems ) or cylinders (for direct injection systems ) coupled with electronic sensors and computers which precisely calculate how long should

2112-406: The amount of fuel or air entering the engine. In a motor vehicle the control used by the driver to regulate power is sometimes called the throttle, accelerator, or gas pedal . For a gasoline engine, the throttle most commonly regulates the amount of air and fuel allowed to enter the engine. However, in a gasoline direct injection engine, the throttle regulates only the amount of air allowed to enter

2176-465: The carburetor high (thus improving efficiency). The "secondary" throttle is operated either mechanically when the primary plate is opened past a certain amount, or via engine vacuum, influenced by the position of the accelerator pedal and engine load, allowing for greater air flow into the engine at high RPM and load and better efficiency at low RPM. Multiple 2-venturi or 4-venturi carburetors can be used simultaneously in situations where maximum engine power

2240-425: The combustion chamber. Reducing the amount of oxygen reduces the amount of fuel that can burn in the cylinder thereby reducing peak in-cylinder temperatures. The actual amount of recirculated exhaust gas varies with the engine operating parameters. In the combustion cylinder, NO x is produced by high-temperature mixtures of atmospheric nitrogen and oxygen, and this usually occurs at cylinder peak pressure. In

2304-488: The combustion temperatures. In modern diesel engines , the EGR gas is usually cooled with a heat exchanger to allow the introduction of a greater mass of recirculated gas. However, uncooled EGR designs do exist; these are often referred to as hot-gas recirculation (HGR). Cooled EGR components are exposed to repeated, rapid changes in temperatures, which can cause coolant leak and catastrophic engine failure. Unlike spark-ignition engines , diesel engines are not limited by

2368-434: The days when many high performance cars were given one, small, single-venturi carburettor for each cylinder or pair of cylinders (i.e. Weber, SU carburettors), each one with their own small throttle plate inside. In a carburettor, the smaller throttle opening also allowed for more precise and fast carburettor response, as well as better atomization of the fuel when running at low engine speeds. Steam locomotives normally have

2432-415: The development of engines that do not require them. The 3.6 Chrysler Pentastar engine is one example that does not require EGR. The exhaust gas contains water vapor and carbon dioxide which both have lower heat capacity ratio than air. Adding exhaust gas therefore reduces pressure and temperature during the isentropic compression in the cylinder, thereby lowering the adiabatic flame temperature . In

2496-462: The displacement was enlarged to 2,467 cc (2.5 L) and this engine produced 175 kW (235 hp). Applications: Throttle body A throttle is a mechanism by which fluid flow is managed by construction or obstruction. An engine 's power can be increased or decreased by the restriction of inlet gases (by the use of a throttle), but usually decreased. The term throttle has come to refer, informally, to any mechanism by which

2560-405: The end of a stage's burn time if it is carrying sensitive cargo (e.g. humans). In a jet engine , thrust is controlled by changing the amount of fuel flowing into the combustion chamber, similar to a diesel engine. The lifespan of the throttle is not set since it highly depends on the driving style and specific vehicle. The throttle tends to be quite dirty after 100-150 thousand kilometers, and it

2624-401: The engine to draw intake air at a certain temperature (the engine's current coolant temperature, which the ECU senses through the relevant sensor ) and therefore with a known density. The largest piece inside the throttle body is the throttle plate, which is a butterfly valve that regulates the airflow. On many cars, the accelerator pedal motion is communicated via the throttle cable, which

BMW S14 - Misplaced Pages Continue

2688-401: The engine. The throttle of a diesel, when present, regulates the air flow into the engine. Historically, the throttle pedal or lever acts via a direct mechanical linkage . The butterfly valve of the throttle is operated by means of an arm piece, loaded by a spring. This arm is usually directly linked to the accelerator cable, and operates in accordance with the driver, who hits it. The further

2752-431: The form of an undesirable positive-feedback loop, will worsen as the engine ages. For example, as the piston rings progressively wear out, more crankcase oil will get into the exhaust stream. Simultaneously, more fuel and soot and combustion byproducts will gain access to the engine oil.) The end result of this recirculation of both exhaust gas and crankcase oil vapour is again an increase in soot production, which however

2816-402: The heat of compression to ignite their fuel, they are fundamentally different from spark-ignited engines. The physical process of diesel-fuel combustion is such that the most complete combustion occurs at the highest temperatures. Unfortunately, the production of nitrogen oxides ( NO x ) increases at high temperatures. The goal of EGR is thus to reduce NO x production by reducing

2880-411: The inclusion of injectors. Most fuel injected cars have a single throttle, contained in a throttle body . Vehicles can sometimes employ more than one throttle body, connected by linkages to operate simultaneously, which improves throttle response and allows a straighter path for the airflow to the cylinder head, as well as for equal-distance intake runners of short length, difficult to achieve when all

2944-502: The intake tract only under certain conditions. Control systems grew more sophisticated as automakers gained experience; Volkswagen's "Coolant Controlled Exhaust Gas Recirculation" system of 1973 exemplified this evolution: a coolant temperature sensor blocked vacuum to the EGR valve until the engine reached normal operating temperature . This prevented driveability problems due to unnecessary exhaust induction; NO x forms under elevated temperature conditions generally not present with

3008-453: The latter is only there to reduce oil vapor emissions, and can be present on engines with or without any EGR system. However, the tripartite mixture resulting from employing both EGR and PCV in an engine (i.e. exhaust gas, fresh air, and oil vapour) can cause the buildup of sticky tar in the intake manifold and valves. This mixture can also cause problems with components such as swirl flaps , where fitted. (These problems, which effectively take

3072-512: The minimum airflow during idle . Even in those units that are not " drive-by-wire ", there will often be a small solenoid driven valve , the Idle Air Control Valve (IACV), that the ECU uses to control the amount of air that can bypass the main throttle opening to allow the engine to idle when the throttle is closed. The most basic carbureted engines, such as single cylinder Briggs & Stratton lawn-mower engines, feature

3136-458: The need for a contiguous flamefront. Furthermore, since diesels always operate with excess air, they benefit (in terms of reduced NO x output) from EGR rates as high as 50%. However, a 50% EGR rate is only suitable when the diesel engine is at idle, since this is when there is otherwise a large excess of air. Because modern diesel engines often have a throttle, EGR can reduce the need for throttling, thereby eliminating this type of loss in

3200-422: The nitrogen dioxide component of NO x emissions is the primary oxidizer of the soot caught in the DPF at normal operating temperatures. This process is known as passive regeneration, and it is only partially effective at burning off the captured soot. And, especially at high EGR rates, the effectiveness of passive regeneration is further reduced. This, in turn, necessitates periodic active regeneration of

3264-400: The others once pressure begins to equalize than to open a single large valve, especially as steam pressures eventually exceeded 200 psi (1,400 kPa) or even 300 psi (2,100 kPa). Examples include the balanced " double beat " type used on Gresley A3 Pacifics . Throttling of a rocket engine means varying the thrust level in-flight. This is not always a requirement; in fact,

SECTION 50

#1732791708407

3328-539: The pedal is pushed, the wider the throttle valve opens. Modern engines of both types (gas and diesel) are commonly drive-by-wire systems where sensors monitor the driver controls and in response a computerized system controls the flow of fuel and air. This means that the operator does not have direct control over the flow of fuel and air; the Engine Control Unit (ECU) can achieve better control in order to reduce emissions , maximize performance and adjust

3392-420: The power or speed of an engine is regulated, such as a car's accelerator pedal. What is often termed a throttle (in an aviation context) is also called a thrust lever , particularly for jet engine powered aircraft. For a steam locomotive , the valve which controls the steam is known as the regulator . In an internal combustion engine , the throttle is a means of controlling an engine's power by regulating

3456-471: The process) and then end up in the crankcase oil, where they will cause further wear throughout the engine simply because their tiny size passes through typical oil filters. This enables them to be recirculated indefinitely (until the next oil change takes place). Exhaust gas—which consists largely of nitrogen, carbon dioxide , and water vapor—has a higher specific heat than air, so it still serves to lower peak combustion temperatures. However, adding EGR to

3520-636: The runners have to travel to certain location to connect to a single throttle body, at the cost of greater complexity and packaging issues. At the extreme, higher-performance cars like the E92 BMW M3 and Ferraris , and high-performance motorcycles like the Yamaha R6 , can use a separate throttle body for each cylinder, often called " individual throttle bodies " or ITBs. Although rare in production vehicles, these are common equipment on many racing cars and modified street vehicles. This practice harks back to

3584-424: The same way that it does for spark-ignited engines. In a naturally aspirated (i.e. nonturbocharged) engine, such a reduction in throttling also reduces the problem of engine oil being sucked past the piston rings into the cylinder and causing oil-derived carbon deposits there. (This benefit only applies to nonturbocharged engines.) In diesel engines in particular, EGR systems come with serious drawbacks, one of which

3648-473: The same, albeit with less pumping losses. In fuel injected engines , the throttle body is the part of the air intake system that controls the amount of air flowing into the engine, in response to driver accelerator pedal input in the main. The throttle body is usually located between the air filter box and the intake manifold , and it is usually attached to, or near, the mass airflow sensor . Often, an engine coolant line also runs through it in order for

3712-401: The specific engine design, and sometimes leads to a compromise between efficiency and NO x emissions. In certain types of situations, a properly operating EGR can theoretically increase the efficiency of gasoline engines via several mechanisms: EGR is typically not employed at high loads because it would reduce peak power output. This is because it reduces the intake charge density. EGR

3776-400: The throttle (North American English) or regulator (British English) in a characteristic steam dome at the top of the boiler (although not all boilers feature these). The additional height afforded by the dome helps to avoid any liquid (e.g. from bubbles on the surface of the boiler water) being drawn into the throttle valve, which could damage it, or lead to priming . The throttle is basically

3840-438: The throttle opening based on the accelerator pedal's position and inputs from other engine sensors such as the engine coolant temperature sensor. When the driver presses on the accelerator pedal, the throttle plate rotates within the throttle body, opening the throttle passage to allow more air into the intake manifold, immediately drawn inside by its vacuum. Usually a mass airflow sensor measures this change and communicates it to

3904-485: The throttle's lifespan is through regular maintenance and cleaning. Exhaust gas recirculation In internal combustion engines , exhaust gas recirculation ( EGR ) is a nitrogen oxide ( NO x ) emissions reduction technique used in petrol/gasoline , diesel engines and some hydrogen engines . EGR works by recirculating a portion of an engine's exhaust gas back to the engine cylinders . The exhaust gas displaces atmospheric air and reduces O 2 in

SECTION 60

#1732791708407

3968-505: The thrust of a solid-fuel rocket is not controllable after ignition. However, liquid-propellant rockets can be throttled by means of valves which regulate the flow of fuel and oxidizer to the combustion chamber. Hybrid rocket engines, such as the one used in Space Ship One , use solid fuel with a liquid oxidizer, and therefore can be throttled. Throttling tends to be required more for powered landings, and launch into space using

4032-436: The time after cold starts during which the engine controller has to inject somewhat larger amounts of fuel into the cylinders to counter the effects of fuel vapor condensation on cylinder walls and lowered combustion effectiveness because of the engine block still being below ideal operating temperature. Lowering combustion temperatures also helps reducing the oxidization of engine oil, as the most significant factor affecting that

4096-452: The vehicle is coasting or cruising). Power is not reduced by EGR at any times, as EGR is not employed in high load engine situations. This allows engines to still deliver maximum power when needed, but lower fuel consumption despite large cylinder volume when partial load is sufficient to meet the power needs of the car and the driver. EGR has nothing to do with oil vapor re-routing from a positive crankcase ventilation system (PCV) system, as

#406593