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86-545: Yamaha Y125Z or better known as Yamaha Z (in Europe, Thailand and Vietnam) is a 125 cc two-stroke moped or underbone motorcycle produced by Yamaha . Debuted in 1998 as a successor of Yamaha Y110SS , the Y125Z was the first two-stroke underbone motorcycle with an YEIS catalytic converter . Beside being sold in most Southeast Asian countries especially in Malaysia and Singapore, it

172-413: A lightning flash. In atmospheric chemistry , the term NO x refers to the total concentration of NO and NO 2 since the conversion between these two species is rapid in the stratosphere and troposphere. During daylight hours, these concentrations together with that of ozone are in steady state , also known as photostationary state (PSS); the ratio of NO to NO 2 is determined by

258-415: A power-valve system . The valves are normally in or around the exhaust ports. They work in one of two ways; either they alter the exhaust port by closing off the top part of the port, which alters port timing, such as Rotax R.A.V.E, Yamaha YPVS, Honda RC-Valve, Kawasaki K.I.P.S., Cagiva C.T.S., or Suzuki AETC systems, or by altering the volume of the exhaust, which changes the resonant frequency of

344-421: A rotary valve is that it enables the two-stroke engine's intake timing to be asymmetrical, which is not possible with piston-port type engines. The piston-port type engine's intake timing opens and closes before and after top dead center at the same crank angle, making it symmetrical, whereas the rotary valve allows the opening to begin and close earlier. Rotary valve engines can be tailored to deliver power over

430-421: A DKW design that proved reasonably successful employing loop charging. The original SAAB 92 had a two-cylinder engine of comparatively low efficiency. At cruising speed, reflected-wave, exhaust-port blocking occurred at too low a frequency. Using the asymmetrical three-port exhaust manifold employed in the identical DKW engine improved fuel economy. The 750-cc standard engine produced 36 to 42 hp, depending on

516-448: A crossflow engine) is always best and support is good. In some engines, the small end is offset to reduce thrust in the intended rotational direction and the forward face of the piston has been made thinner and lighter to compensate, but when running backward, this weaker forward face suffers increased mechanical stress it was not designed to resist. This can be avoided by the use of crossheads and also using thrust bearings to isolate

602-557: A fairly inert oxide of nitrogen that contributes less severely to air pollution, notwithstanding its involvement in ozone depletion and high global warming potential . NO y is the class of compounds comprising NO x and the NO z compounds produced from the oxidation of NO x which include nitric acid , nitrous acid (HONO), dinitrogen pentoxide ( N 2 O 5 ), peroxyacetyl nitrate (PAN), alkyl nitrates ( RONO 2 ), peroxyalkyl nitrates ( ROONO 2 ),

688-630: A higher power-to-weight ratio than a four-stroke engine, since their power stroke occurs twice as often. Two-stroke engines can also have fewer moving parts , and thus be cheaper to manufacture and weigh less. In countries and regions with stringent emissions regulation, two-stroke engines have been phased out in automotive and motorcycle uses. In regions where regulations are less stringent, small displacement two-stroke engines remain popular in mopeds and motorcycles. They are also used in power tools such as chainsaws and leaf blowers . The first commercial two-stroke engine involving cylinder compression

774-465: A patent in 1880 in Germany. The first truly practical two-stroke engine is attributed to Yorkshireman Alfred Angas Scott , who started producing twin-cylinder water-cooled motorcycles in 1908. Two-stroke gasoline engines with electrical spark ignition are particularly useful in lightweight or portable applications such as chainsaws and motorcycles. However, when weight and size are not an issue,

860-475: A ratio greater than or equal to the stoichiometric combustion requirement. Water Injection technology, whereby water is introduced into the combustion chamber, is also becoming an important means of NO x reduction through increased efficiency in the overall combustion process. Alternatively, the water (e.g. 10 to 50%) is emulsified into the fuel oil before the injection and combustion. This emulsification can either be made in-line (unstabilized) just before

946-449: A scavenging function. The units run in pairs, with the lower half of one piston charging an adjacent combustion chamber. The upper section of the piston still relies on total-loss lubrication, but the other engine parts are sump lubricated with cleanliness and reliability benefits. The mass of the piston is only about 20% more than a loop-scavenged engine's piston because skirt thicknesses can be less. Many modern two-stroke engines employ

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1032-658: A similar system. Traditional flywheel magnetos (using contact-breaker points, but no external coil) worked equally well in reverse because the cam controlling the points is symmetrical, breaking contact before top dead center equally well whether running forward or backward. Reed-valve engines run backward just as well as piston-controlled porting, though rotary valve engines have asymmetrical inlet timing and do not run very well. Serious disadvantages exist for running many engines backward under load for any length of time, and some of these reasons are general, applying equally to both two-stroke and four-stroke engines. This disadvantage

1118-489: A source of NO x over the ocean. Then, photolysis of NO 2 leads to the formation of ozone and the further formation of hydroxyl radicals (·OH) through ozone photolysis. Since the major sink of methane in the atmosphere is by reaction with OH radicals, the NO x emissions from ship travel may lead to a net global cooling. However, NO x in the atmosphere may undergo dry or wet deposition and return to land in

1204-568: A special formulation of diesel fuel to produce less NO x relative to diesel fuel used in the other 49 states. This has been deemed necessary by the California Air Resources Board (CARB) to offset the combination of vehicle congestion, warm temperatures, extensive sunlight, PM, and topography that all contribute to the formation of ozone and smog. CARB has established a special regulation for Alternative Diesel Fuels to ensure that any new fuels, including biodiesel, coming into

1290-485: A third molecule required to stabilize the addition product. Nitric acid ( HNO 3 ) is highly soluble in liquid water in aerosol particles or cloud drops. NO 2 also reacts with ozone to form nitrate radical During the daytime, NO 3 is quickly photolyzed back to NO 2 , but at night it can react with a second NO 2 to form dinitrogen pentoxide . N 2 O 5 reacts rapidly with liquid water (in aerosol particles or cloud drops, but not in

1376-551: A tradeoff exists as high temperature combustion produces less PM or soot and results in greater power and fuel efficiency . Selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR) reduce post combustion NO x by reacting the exhaust with urea or ammonia to produce nitrogen and water. SCR is now being used in ships, diesel trucks and in some diesel cars. The use of exhaust gas recirculation and catalytic converters in motor vehicle engines have significantly reduced vehicular emissions . NO x

1462-518: A turbocharger. Crankcase-compression two-stroke engines, such as common small gasoline-powered engines, are lubricated by a petroil mixture in a total-loss system . Oil is mixed in with their petrol fuel beforehand, in a fuel-to-oil ratio of around 32:1. This oil then forms emissions, either by being burned in the engine or as droplets in the exhaust, historically resulting in more exhaust emissions, particularly hydrocarbons, than four-stroke engines of comparable power output. The combined opening time of

1548-400: A wider speed range or higher power over a narrower speed range than either a piston-port or reed-valve engine. Where a portion of the rotary valve is a portion of the crankcase itself, of particular importance, no wear should be allowed to take place. In a cross-flow engine, the transfer and exhaust ports are on opposite sides of the cylinder, and a deflector on the top of the piston directs

1634-413: Is accepted in most cases where cost, weight, and size are major considerations. The problem comes about because in "forward" running, the major thrust face of the piston is on the back face of the cylinder, which in a two-stroke particularly, is the coolest and best-lubricated part. The forward face of the piston in a trunk engine is less well-suited to be the major thrust face, since it covers and uncovers

1720-609: Is associated with a number of factors such as combustion temperature. As such, it can be observed that the vehicle drive cycle, or the load on the engine have more significant impact on NO x emissions than the type of fuel used. This may be especially true for modern, clean diesel vehicles that continuously monitor engine operation electronically and actively control engine parameters and exhaust system operations to limit NO x emission to less than 0.2 g/km. Low-temperature combustion or LTC technology may help reduce thermal formation of NO x during combustion, however

1806-563: Is associated with the combustion of nitrogen present in the feed material of cement rotary kilns, at between 300 °C and 800 °C, where it is considered a minor contributor. Thermal NO x refers to NO x formed through high temperature oxidation of the diatomic nitrogen found in combustion air. The formation rate is primarily a function of temperature and the residence time of nitrogen at that temperature. At high temperatures, usually above 1300 °C (2600 °F), molecular nitrogen ( N 2 ) and oxygen ( O 2 ) in

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1892-422: Is attributed to Scottish engineer Dugald Clerk , who patented his design in 1881. However, unlike most later two-stroke engines, his had a separate charging cylinder. The crankcase -scavenged engine, employing the area below the piston as a charging pump, is generally credited to Englishman Joseph Day . On 31 December 1879, German inventor Karl Benz produced a two-stroke gas engine, for which he received

1978-590: Is being phased out. Honda , for instance, ceased selling two-stroke off-road motorcycles in the United States in 2007, after abandoning road-going models considerably earlier. Due to their high power-to-weight ratio and ability to be used in any orientation, two-stroke engines are common in handheld outdoor power tools including leaf blowers , chainsaws , and string trimmers . Two-stroke diesel engines are found mostly in large industrial and marine applications, as well as some trucks and heavy machinery. Although

2064-565: Is common in on-road, off-road, and stationary two-stroke engines ( Detroit Diesel ), certain small marine two-stroke engines ( Gray Marine Motor Company , which adapted the Detroit Diesel Series 71 for marine use ), certain railroad two-stroke diesel locomotives ( Electro-Motive Diesel ) and large marine two-stroke main propulsion engines ( Wärtsilä ). Ported types are represented by the opposed piston design in which two pistons are in each cylinder, working in opposite directions such as

2150-616: Is emitted during its application, it is then reacted in atmosphere to form nitrogen oxides. This third source is attributed to the reaction of atmospheric nitrogen, N 2 , with radicals such as C, CH, and CH 2 fragments derived from fuel, rather than thermal or fuel processes. Occurring in the earliest stage of combustion, this results in the formation of fixed species of nitrogen such as NH ( nitrogen monohydride ), NCN ( diradical cyano nitrene ), HCN ( hydrogen cyanide ), H 2 CN ( dihydrogen cyanide ) and CN ( cyano radical) which can oxidize to NO. In fuels that contain nitrogen,

2236-430: Is highly temperature dependent, is recognized as the most relevant source when combusting natural gas. Fuel NO x tends to dominate during the combustion of fuels, such as coal, which have a significant nitrogen content, particularly when burned in combustors designed to minimise thermal NO x . The contribution of prompt NO x is normally considered negligible. A fourth source, called feed NO x

2322-438: Is intensifying global warming. There are also other indirect effects of NO x that can either increase or decrease the greenhouse effect. First of all, through the reaction of NO with HO 2 · radicals, OH radicals are recycled, which oxidize methane molecules, meaning NO x emissions can counter the effect of greenhouse gases. For instance, ship traffic emits a great amount of NO x which provides

2408-591: Is reduced to nitrite, then NO, then N 2 O and finally nitrogen. Through these processes, NO x is emitted to the atmosphere. A recent study conducted by the University of California Davis found that adding nitrogen fertilizer to soil in California is contributing 25 percent or more to state-wide NO x pollution levels. When nitrogen fertilizer is added to the soil, excess ammonium and nitrate not used by plants can be converted to NO by microorganisms in

2494-432: Is that the two-stroke's crankcase is sealed and forms part of the induction process in gasoline and hot-bulb engines . Diesel two-strokes often add a Roots blower or piston pump for scavenging . The reed valve is a simple but highly effective form of check valve commonly fitted in the intake tract of the piston-controlled port. It allows asymmetric intake of the fuel charge, improving power and economy, while widening

2580-409: Is under every circumstance more efficient than cross-flow scavenging. In a uniflow engine, the mixture, or "charge air" in the case of a diesel, enters at one end of the cylinder controlled by the piston and the exhaust exits at the other end controlled by an exhaust valve or piston. The scavenging gas-flow is, therefore, in one direction only, hence the name uniflow. The design using exhaust valve(s)

2666-458: The Junkers Jumo 205 and Napier Deltic . The once-popular split-single design falls into this class, being effectively a folded uniflow. With advanced-angle exhaust timing, uniflow engines can be supercharged with a crankshaft-driven blower, either piston or Roots-type. The piston of this engine is "top-hat"-shaped; the upper section forms the regular cylinder, and the lower section performs

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2752-506: The expansion chamber , such as the Suzuki SAEC and Honda V-TACS system. The result is an engine with better low-speed power without sacrificing high-speed power. However, as power valves are in the hot gas flow, they need regular maintenance to perform well. Direct injection has considerable advantages in two-stroke engines. In carburetted two-strokes, a major problem is a portion of the fuel/air mixture going directly out, unburned, through

2838-473: The oil reservoir does not depend on gravity. A number of mainstream automobile manufacturers have used two-stroke engines in the past, including the Swedish Saab , German manufacturers DKW , Auto-Union , VEB Sachsenring Automobilwerke Zwickau , VEB Automobilwerk Eisenach , and VEB Fahrzeug- und Jagdwaffenwerk , and Polish manufacturers FSO and FSM . The Japanese manufacturers Suzuki and Subaru did

2924-528: The 1960s due in no small way to the increased power afforded by loop scavenging. An additional benefit of loop scavenging was the piston could be made nearly flat or slightly domed, which allowed the piston to be appreciably lighter and stronger, and consequently to tolerate higher engine speeds. The "flat top" piston also has better thermal properties and is less prone to uneven heating, expansion, piston seizures, dimensional changes, and compression losses. SAAB built 750- and 850-cc three-cylinder engines based on

3010-407: The 1960s, especially for motorcycles, but for smaller or slower engines using direct injection, the deflector piston can still be an acceptable approach. This method of scavenging uses carefully shaped and positioned transfer ports to direct the flow of fresh mixture toward the combustion chamber as it enters the cylinder. The fuel/air mixture strikes the cylinder head , then follows the curvature of

3096-448: The German inventor of an early form in the mid-1920s, it became widely adopted in Germany country during the 1930s and spread further afield after World War II . Loop scavenging is the most common type of fuel/air mixture transfer used on modern two-stroke engines. Suzuki was one of the first manufacturers outside of Europe to adopt loop-scavenged, two-stroke engines. This operational feature

3182-459: The air. Elevated production of NO x from lightning depends on the season and geographic location. The occurrence of lightning is more common over land near the equator in the inter-tropical convergence zone (ITCZ) during summer months. This area migrates slightly as seasons change. NO x production from lightning can be observed through satellite observations. Scientists Ott et al. estimated that each flash of lightning on average in

3268-423: The bore diameter for reasonable piston ring life. Beyond this, the piston rings bulge into the exhaust port and wear quickly. A maximum 70% of bore width is possible in racing engines, where rings are changed every few races. Intake duration is between 120 and 160°. Transfer port time is set at a minimum of 26°. The strong, low-pressure pulse of a racing two-stroke expansion chamber can drop the pressure to -7 psi when

3354-435: The combustion air dissociate into their atomic states and participate in a series of reactions. The three principal reactions (the extended Zel'dovich mechanism ) producing thermal NO x are: All three reactions are reversible. Zeldovich was the first to suggest the importance of the first two reactions. The last reaction of atomic nitrogen with the hydroxyl radical , HO, was added by Lavoie, Heywood and Keck to

3440-459: The combustion chamber, and then is deflected downward. This not only prevents the fuel/air mixture from traveling directly out the exhaust port, but also creates a swirling turbulence which improves combustion efficiency , power, and economy. Usually, a piston deflector is not required, so this approach has a distinct advantage over the cross-flow scheme (above). Often referred to as "Schnuerle" (or "Schnürle") loop scavenging after Adolf Schnürle,

3526-416: The combustion of the char portion of the fuels. This reaction occurs much more slowly than the volatile phase. Only around 20% of the char nitrogen is ultimately emitted as NO x , since much of the NO x that forms during this process is reduced to nitrogen by the char, which is nearly pure carbon. Nitrogen oxides are released during manufacturing of nitrogen fertilizers. Though nitrous oxide

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3612-411: The concentration of ozone and peroxide compounds, especially peroxyacetyl nitrate (PAN). Children, people with lung diseases such as asthma , and people who work or exercise outside are particularly susceptible to adverse effects of smog such as damage to lung tissue and reduction in lung function. NO 2 is further oxidized in the gas phase during daytime by reaction with OH where M denotes

3698-601: The countryside and in suburbs, while in central London and on major roads NO emissions are able to "mop up" ozone to form NO 2 and oxygen. NO x also readily reacts with common organic chemicals, and even ozone, to form a wide variety of toxic products: nitroarenes , nitrosamines and also the nitrate radical some of which may cause DNA mutations . Recently another pathway, via NO x , to ozone has been found that predominantly occurs in coastal areas via formation of nitryl chloride when NO x comes into contact with salt mist. The direct effect of

3784-453: The crankshaft commonly spins in the same axis and direction as do the wheels i.e. "forward". Some of the considerations discussed here apply to four-stroke engines (which cannot reverse their direction of rotation without considerable modification), almost all of which spin forward, too. It is also useful to note that the "front" and "back" faces of the piston are - respectively - the exhaust port and intake port sides of it, and are not to do with

3870-415: The cycle's potential for high thermodynamic efficiency makes it ideal for diesel compression ignition engines operating in large, weight-insensitive applications, such as marine propulsion , railway locomotives , and electricity generation . In a two-stroke engine, the exhaust gases transfer less heat to the cooling system than a four-stroke, which means more energy to drive the piston, and if present,

3956-487: The eastern United States can expect to see increases in NO x and in turn, changes in the types of trees which predominate. Due to human activity and climate change , the maples , sassafras , and tulip poplar have been pushing out the beneficial oak , beech , and hickory . The team determined that the first three tree species, maples, sassafras, and tulip poplar, are associated with ammonia-oxidizing bacteria known to "emit reactive nitrogen from soil." By contrast,

4042-522: The emission of NO x has positive contribution to the greenhouse effect. Instead of reacting with ozone in Reaction 3, NO can also react with HO 2 · and organic peroxyradicals ( RO 2 · ) and thus increase the concentration of ozone. Once the concentration of NO x exceeds a certain level, atmospheric reactions result in net ozone formation. Since tropospheric ozone can absorb infrared radiation, this indirect effect of NO x

4128-400: The engine from end loads. Large two-stroke ship diesels are sometimes made to be reversible. Like four-stroke ship engines (some of which are also reversible), they use mechanically operated valves, so require additional camshaft mechanisms. These engines use crossheads to eliminate sidethrust on the piston and isolate the under-piston space from the crankcase. On top of other considerations,

4214-415: The exhaust port in the cylinder, the hottest part of the engine, where piston lubrication is at its most marginal. The front face of the piston is also more vulnerable since the exhaust port, the largest in the engine, is in the front wall of the cylinder. Piston skirts and rings risk being extruded into this port, so having them pressing hardest on the opposite wall (where there are only the transfer ports in

4300-409: The exhaust port, and direct injection effectively eliminates this problem. Two systems are in use: low-pressure air-assisted injection and high-pressure injection. Since the fuel does not pass through the crankcase, a separate source of lubrication is needed. For the purpose of this discussion, it is convenient to think in motorcycle terms, where the exhaust pipe faces into the cooling air stream, and

4386-470: The exothermic reaction 2 . Equation 4 relates the concentrations of NO x and ozone, and is known as the Leighton relationship . The time τ {\displaystyle \tau } that is needed to reach a steady state among NO x and ozone is dominated by reaction ( 3 ), which reverses reactions ( 1 )+( 2 ): for mixing ratio of NO, [NO] = 10 part per billion (ppb),

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4472-405: The extreme heating and cooling within a lightning strike. This causes stable molecules such as N 2 and O 2 to convert into significant amounts of NO similar to the process that occurs during high temperature fuel combustion. NO x from lightning can become oxidized to produce nitric acid ( HNO 3 ), this can be precipitated out as acid rain or deposited onto particles in

4558-670: The form of HNO 3 / NO − 3 . Through this way, the deposition leads to nitrogen fertilization and the subsequent formation of nitrous oxide ( N 2 O ) in soil, which is another greenhouse gas. In conclusion, considering several direct and indirect effects, NO x emissions have a negative contribution to global warming. NO x in the atmosphere is removed through several pathways. During daytime, NO 2 reacts with hydroxyl radicals (·OH) and forms nitric acid ( HNO 3 ), which can easily be removed by dry and wet deposition. Organic peroxyradicals ( RO 2 · ) can also react with NO and NO 2 and result in

4644-790: The formation of organic nitrates . These are ultimately broken down to inorganic nitrate, which is a useful nutrient for plants. During nighttime, NO 2 and NO can form nitrous acid (HONO) through surface-catalyzed reaction. Although the reaction is relatively slow, it is an important reaction in urban areas. In addition, the nitrate radical ( NO 3 ) is formed by the reaction between NO 2 and ozone. At night, NO 3 further reacts with NO 2 and establishes an equilibrium reaction with dinitrogen pentoxide ( N 2 O 5 ). Via heterogeneous reaction, N 2 O 5 reacts with water vapor or liquid water and forms nitric acid ( HNO 3 ). As mentioned above, nitric acid can be removed through wet and dry deposition and this results in

4730-413: The fresh intake charge into the upper part of the cylinder, pushing the residual exhaust gas down the other side of the deflector and out the exhaust port. The deflector increases the piston's weight and exposed surface area, and the fact that it makes piston cooling and achieving an effective combustion chamber shape more difficult is why this design has been largely superseded by uniflow scavenging after

4816-411: The gas phase) to form HNO 3 , These are thought to be the principal pathways for formation of nitric acid in the atmosphere. This nitric acid contributes to acid rain or may deposit to soil, where it makes nitrate , which is of use to growing plants. The aqueous phase reaction is too slow to be of any significance in the atmosphere. Nitric oxide is produced during thunderstorms due to

4902-673: The incidence of prompt NO x is comparatively small and it is generally only of interest for the most exacting emission targets. There is strong evidence that NO x respiratory exposure can trigger and exacerbate existing asthma symptoms, and may even lead to the development of asthma over longer periods of time. It has also been associated with heart disease, diabetes, birth outcomes, and all-cause mortality, but these nonrespiratory effects are less well-established. NO x reacts with ammonia , moisture, and other compounds to form nitric acid vapor and related particles. NO x reacts with volatile organic compounds in

4988-408: The initial stages of combustion. During the release and before the oxidation of the volatiles, nitrogen reacts to form several intermediaries which are then oxidized into NO. If the volatiles evolve into a reducing atmosphere, the nitrogen evolved can readily be made to form nitrogen gas, rather than NO x . The second pathway involves the combustion of nitrogen contained in the char matrix during

5074-443: The intake and exhaust ports in some two-stroke designs can also allow some amount of unburned fuel vapors to exit in the exhaust stream. The high combustion temperatures of small, air-cooled engines may also produce NO x emissions. Two-stroke gasoline engines are preferred when mechanical simplicity, light weight, and high power-to-weight ratio are design priorities. By mixing oil with fuel, they can operate in any orientation as

5160-418: The intensity of sunshine (which converts NO 2 to NO) and the concentration of ozone (which reacts with NO to again form NO 2 ). In other words, the concentration of ozone in the atmosphere is determined by the ratio of these two species. The symbol M {\displaystyle {\ce {M}}} represents a "third body", a molecular species that is required to carry away energy from

5246-455: The market do not substantially increase NO x emissions. The reduction of NO x emissions is one of the most important challenges for advances in vehicle technology. While diesel vehicles sold in the US since 2010 are dramatically cleaner than previous diesel vehicles, urban areas continue to seek more ways to reduce the formation of smog and ozone. NO x formation during combustion

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5332-404: The mechanism and makes a significant contribution to the formation of thermal NO x . It is estimated that transportation fuels cause 54% of the anthropogenic (i.e. human-caused) NO x . The major source of NO x production from nitrogen-bearing fuels such as certain coals and oil, is the conversion of fuel bound nitrogen to NO x during combustion. During combustion,

5418-469: The model year. The Monte Carlo Rally variant, 750-cc (with a filled crankshaft for higher base compression), generated 65 hp. An 850-cc version was available in the 1966 SAAB Sport (a standard trim model in comparison to the deluxe trim of the Monte Carlo). Base compression comprises a portion of the overall compression ratio of a two-stroke engine. Work published at SAE in 2012 points that loop scavenging

5504-434: The nitrate radical ( NO 3 ), and peroxynitric acid ( HNO 4 ). Because of energy limitations, oxygen and nitrogen do not react at ambient temperatures. But at high temperatures, they undergo an endothermic reaction producing various oxides of nitrogen. Such temperatures arise inside an internal combustion engine or a power station boiler , during the combustion of a mixture of air and fuel, and naturally in

5590-427: The nitrogen bound in the fuel is released as a free radical and ultimately forms free N 2 , or NO. Fuel can contribute as much as 50% of total NO x emissions through the combusting oil and as much as 80% through the combusting of coal Although the complete mechanism is not fully understood, there are two primary pathways of formation. The first involves the oxidation of volatile nitrogen species during

5676-438: The number of lightning strikes occurring on Earth. Therefore, space weather can be a major driving force of lightning-produced atmospheric NO x . Atmospheric constituents such as nitrogen oxides can be stratified vertically in the atmosphere. Ott noted that the lightning-produced NO x is typically found at altitudes greater than 5 km, while combustion and biogenic (soil) NO x are typically found near

5762-399: The oil pump of a modern two-stroke may not work in reverse, in which case the engine suffers oil starvation within a short time. Running a motorcycle engine backward is relatively easy to initiate, and in rare cases, can be triggered by a back-fire. It is not advisable. Model airplane engines with reed valves can be mounted in either tractor or pusher configuration without needing to change

5848-483: The other - the inlet pipe having passage to the crankcase only when the two cutouts coincide. The crankshaft itself may form one of the members, as in most glow-plug model engines. In another version, the crank disc is arranged to be a close-clearance fit in the crankcase, and is provided with a cutout that lines up with an inlet passage in the crankcase wall at the appropriate time, as in Vespa motor scooters. The advantage of

5934-434: The piston covering and uncovering the ports as it moves up and down in the cylinder. In the 1970s, Yamaha worked out some basic principles for this system. They found that, in general, widening an exhaust port increases the power by the same amount as raising the port, but the power band does not narrow as it does when the port is raised. However, a mechanical limit exists to the width of a single exhaust port, at about 62% of

6020-440: The piston is at bottom dead center, and the transfer ports nearly wide open. One of the reasons for high fuel consumption in two-strokes is that some of the incoming pressurized fuel-air mixture is forced across the top of the piston, where it has a cooling action, and straight out the exhaust pipe. An expansion chamber with a strong reverse pulse stops this outgoing flow. A fundamental difference from typical four-stroke engines

6106-550: The power band. Such valves are widely used in motorcycle, ATV, and marine outboard engines. The intake pathway is opened and closed by a rotating member. A familiar type sometimes seen on small motorcycles is a slotted disk attached to the crankshaft , which covers and uncovers an opening in the end of the crankcase, allowing charge to enter during one portion of the cycle (called a disc valve). Another form of rotary inlet valve used on two-stroke engines employs two cylindrical members with suitable cutouts arranged to rotate one within

6192-518: The presence of sunlight to form ozone . Ozone can cause adverse effects such as damage to lung tissue and reduction in lung function mostly in susceptible populations (children, elderly, asthmatics). Ozone can be transported by wind currents and cause health impacts far from the original sources. The American Lung Association estimates that nearly 50 percent of United States inhabitants live in counties that are not in ozone compliance. In South East England, ground level ozone pollution tends to be highest in

6278-466: The principles remain the same, the mechanical details of various two-stroke engines differ depending on the type. The design types vary according to the method of introducing the charge to the cylinder, the method of scavenging the cylinder (exchanging burnt exhaust for fresh mixture) and the method of exhausting the cylinder. Piston port is the simplest of the designs and the most common in small two-stroke engines. All functions are controlled solely by

6364-522: The propeller. These motors are compression ignition, so no ignition timing issues and little difference between running forward and running backward are seen. NOx In atmospheric chemistry , NO x is shorthand for nitric oxide ( NO ) and nitrogen dioxide ( NO 2 ), the nitrogen oxides that are most relevant for air pollution . These gases contribute to the formation of smog and acid rain , as well as affecting tropospheric ozone . NO x gases are usually produced from

6450-433: The reaction between nitrogen and oxygen during combustion of fuels, such as hydrocarbons , in air; especially at high temperatures, such as in car engines. In areas of high motor vehicle traffic, such as in large cities, the nitrogen oxides emitted can be a significant source of air pollution. NO x gases are also produced naturally by lightning . NO x does not include nitrous oxide ( N 2 O ),

6536-659: The removal of NO x from the atmosphere. Biodiesel and its blends in general are known to reduce harmful tailpipe emissions such as: carbon monoxide ; particulate matter (PM), otherwise known as soot ; and unburned hydrocarbon emissions. While earlier studies suggested biodiesel could sometimes decrease NO x and sometimes increase NO x emissions, subsequent investigation has shown that blends of up to 20% biodiesel in USEPA-approved diesel fuel have no significant impact on NO x emissions compared with regular diesel . The state of California uses

6622-806: The same in the 1970s. Production of two-stroke cars ended in the 1980s in the West, due to increasingly stringent regulation of air pollution . Eastern Bloc countries continued until around 1991, with the Trabant and Wartburg in East Germany. Two-stroke engines are still found in a variety of small propulsion applications, such as outboard motors , small on- and off-road motorcycles , mopeds , motor scooters , motorized bicycles , tuk-tuks , snowmobiles , go-karts , RC cars , ultralight and model airplanes. Particularly in developed countries, pollution regulations have meant that their use for many of these applications

6708-491: The second three tree species, oak, beech and hickory, are associated with microbes that "absorb reactive nitrogen oxides," and thus can have a positive impact on the nitrogen oxide component of air quality. Nitrogen oxide release from forest soils is expected to be highest in Indiana, Illinois, Michigan, Kentucky and Ohio. The three primary sources of NO x in combustion processes: Thermal NO x formation, which

6794-543: The several mid-latitude and subtropical thunderstorms studied turned 7 kg (15 lb) of nitrogen into chemically reactive NO x . With 1.4 billion lightning flashes per year, multiplied by 7 kilograms per lightning strike, they estimated the total amount of NO x produced by lightning per year is 8.6 million tonnes. However, NO x emissions resulting from fossil fuel combustion are estimated at 28.5 million tonnes. A recent discovery indicated that cosmic ray and solar flares can significantly influence

6880-482: The soil, which escapes into the air. NO x is a precursor for smog formation which is already a known issue for the state of California. In addition to contributing to smog, when nitrogen fertilizer is added to the soil and the excess is released in the form of NO, or leached as nitrate this can be a costly process for the farming industry. A 2018 study by the Indiana University determined that forests in

6966-427: The sources at near surface elevation (where it can cause the most significant health effects). Agricultural fertilization and the use of nitrogen fixing plants also contribute to atmospheric NO x , by promoting nitrogen fixation by microorganisms. The nitrification process transforms ammonia into nitrate. Denitrification is basically the reverse process of nitrification. During denitrification, nitrate

7052-453: The time constant is 40 minutes; for [NO] = 1 ppb, 4 minutes. When NO x and volatile organic compounds (VOCs) react in the presence of sunlight, they form photochemical smog , a significant form of air pollution. The presence of photochemical smog increases during the summer when the incident solar radiation is higher. The emitted hydrocarbons from industrial activities and transportation react with NO x quickly and increase

7138-511: The top or bottom of the piston. Regular gasoline two-stroke engines can run backward for short periods and under light load with little problem, and this has been used to provide a reversing facility in microcars , such as the Messerschmitt KR200 , that lacked reverse gearing. Where the vehicle has electric starting, the motor is turned off and restarted backward by turning the key in the opposite direction. Two-stroke golf carts have used

7224-582: Was also sold in Greece. The production of the Y125Z ended in 2017 after being sold for more than two decades. The Yamaha Y125Z is widely used in motorcycle racing tournaments held in Malaysia or Asean level. In Malaysia, the Y125Z is formerly used in the Expert category of Malaysian Cub Prix tournament series. This motorcycle, scooter or moped-related article is a stub . You can help Misplaced Pages by expanding it . Two-stroke Two-stroke engines often have

7310-532: Was the main focus of the Volkswagen emissions violations . Other technologies such as flameless oxidation ( FLOX ) and staged combustion significantly reduce thermal NO x in industrial processes. Bowin low NO x technology is a hybrid of staged-premixed-radiant combustion technology with major surface combustion preceded by minor radiant combustion. In the Bowin burner, air and fuel gas are premixed at

7396-530: Was used in conjunction with the expansion chamber exhaust developed by German motorcycle manufacturer, MZ, and Walter Kaaden. Loop scavenging, disc valves, and expansion chambers worked in a highly coordinated way to significantly increase the power output of two-stroke engines, particularly from the Japanese manufacturers Suzuki, Yamaha, and Kawasaki. Suzuki and Yamaha enjoyed success in Grand Prix motorcycle racing in

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