Last March at the Geneva Motor Show, Lotus announced its new Omnivore research engine. The Omnivore is a two-stroke direct injected engine designed to take advantage of the latest in electronic engine direction to let it to run on merely about any liquid fuel. In the clip since the initial proclamation, the boffins at Lotus Engineering have been exerting their creative activity on the dyno base to measure the public presentation. Lotus claims the Omnivore is ideally suited to flex-fuel operation with a higher grade of optimisation than is possible with bing four shot engines. The variable compaction ratio is achieved by the usage of a Puck at the top of the burning chamber. This simple, yet effectual system moves up and down impacting the alteration in geometric compaction depending on the burden demands on the engine.
The single-cylinder engine uses an air-assisted direct injection system. A movable “ Puck ” in the top of the cylinder caput allows the compaction ratio to be varied.
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The motor uses the Orbital FlexDI fuel injection system which produces all right in-cylinder fuel readying irrespective of fuel type, and together with air pre-mixing allows efficient two-stroke burning and low-temperature starting, whilst offering remarkable chance for advanced HCCI control. The engine has so far been run on gasolene and in both spark ignition and homogenous charge compaction ignition ( HCCI ) manners. The HCCI manner is of peculiar involvement because it is capable of supplying diesel engine-like efficiency without the particulate and NOx emanations that require expensive after-treatment systems in a standard Diesel engine. Lotus is claiming the Omnivore can run in HCCI manner in a broad assortment of operating conditions and even from a cold start, something that has been debatable for old HCCI engines. Harmonizing to the initial trial consequences, the Omnivore is accomplishing up to a 10 per centum betterment in efficiency compared to bing spark ignition direct injected engines.
The Omnivore plan is another measure in Lotus ‘ research into the burning processes involved in running an engine on mixtures of intoxicant based fuels and gasolene, which included the Lotus Exige 270E Tri-fuel, unveiled at the International Geneva Motor Show in 2008
there is clearly a batch of work yet to make as we are working on pin downing valve in this undertaking.
What are 2-stroke engine?
In two-stroke engine rhythm engines the rhythm of operation is completed in two shot merely and each outward shot of the Piston is power or enlargement shot. The engine Piston needs merely to compact the fresh charge and to spread out the merchandises of burning, such operation is made possible by the fact that the pumping map in non carried out in the on the job cylinders but it accomplished either in a separate mechanism called the scavenging pump or in an enclosed crankcase with the dorsum of the engine Piston being used as a scavenging pump. The fresh charge is supplied to the engine cylinder at a high adequate force per unit area to displace the burnt gases from the old rhythm. The operation of uncluttering the exhaust gases from the cylinder and make fulling it more or less wholly with fresh charge is called scavenging. The procedure of scavenging includes both the consumption and the exhaust procedures.
Many two shot engines use the Piston as a slide valve in concurrence with the recess and exhaust ports on the side of the cylinder. This agreement greatly simplifies the mechanical building of the engine. Very big Marine engines and really little reciprocating Piston engines are two-stroke engines.
is an internal burning engine that completes the thermodynamic rhythm in two motions of the Piston ( compared to twice that figure for a four-stroke engine ) . This increased efficiency is accomplished by utilizing the beginning of the compaction shot and the terminal of the burning stroke to execute at the same time the consumption and exhaust maps. In this manner two-stroke engines frequently provide strikingly high specific power. Gasoline ( spark ignition ) versions are peculiarly utile in lightweight applications such as chain saws and the construct is besides used in diesel compaction ignition engines in big and non-weight sensitive applications such as ships and engines.
Problems of the two-stroke engine
really the two-stroke engine should execute twice the public presentation of a four-stroke engine with the same three-dimensional capacity. Though it is merely possible to derive a public presentation that is approximately 50 % better. The grounds are obvious: The cylinder ca n’t be filled up with the same sum of fuel as in the four-stroke engine, because the single shots are separated non so clearly. If more fuel is induced, it leaves the burning chamber through the expulsion pipe without being burned. Many constructs were developed to supply a better ejection of the fumes in manner that the fresh gas does n’t go forth the burning chamber. Though all these innovations, the filling of the two-stroke engine is ever worse than in the four-stroke engine, which loses fresh fuel merely because of the “ overlap ” of the valve times ( both valves are unfastened for an blink of an eye ) . Beside these performance-technical jobs, there are besides increasing troubles with the environment. The fuel mixture of the two-stroke engine frequently gets shifted with a certain measure of oil because of the necessary lubrication. Unfortunately the oil gets burnt partially, excessively, and harmful gases are expulsed by the engine.
Gasoline direct injection:
In internal burning engines, Gasoline Direct Injection ( GDI ) , sometimes known as Fuel Stratified Injection ( FSI ) , is an progressively popular type of fuel injection system employed in modern four and two-stroke gasoline engines. The petrol/gasoline is extremely pressurised, and injected by high electromotive force driven injectors via a common rail fuel line straight into the burning chamber of each cylinder, as opposed to conventional individual or multi-point fuel injection that happens in the consumption manifold piece of land, or cylinder port. In some applications, gasolene direct injection enables a graded fuel charge ( extremist thin burn ) burning for improved fuel efficiency, and decreased emanation degrees at low burden.
Basic theory of operation:
The major advantages of a GDI engine are lower emanation degrees, increased fuel efficiency and higher engine power end product. In add-on, the chilling consequence of the injected fuel and the more equally spread burning mixtures and temperatures allow for improved ignition timing scenes which are an every bit of import system demand.
Emissions degrees can be more accurately controlled with the GDI system. The lower degrees are achieved by the precise control over the sum of fuel, air and ignition scenes which are varied harmonizing to the engine burden conditions and ambient air temperatures.
In add-on, there are no restricting losingss in some
GDI designed engines, when compared to a conventional fuel injected or carbureted engine, which greatly improves efficiency and reduces ‘pumping losingss ‘ in engines without a throttle home base. Engine velocity is controlled by the engine direction system which regulates fuel injection and ignition timing parametric quantities, alternatively of holding a accelerator home base which restricts the incoming air supply. Adding this map to the engine direction system requires considerable sweetening of its processing and memory, as direct injection plus other engine direction systems must hold really precise function for good public presentation and driveability.
The engine direction system continually chooses among three burning
rhythms: extremist thin burn, stoichiometric, and full power end product. Each rhythm is characterised by the air-fuel ratio. The stoichiometric air-fuel ratio for gasoline ( gasolene ) engines is 14.7:1 by weight, but the extremist thin rhythm can affect ratios every bit high as 35:1 ( or even higher in some engines, for really limited periods ) . These mixtures are much leaner than in a conventional fuel injected engine and cut down fuel ingestion and certain degrees of exhaust emanations well.
Direct injection is supported by other engine direction systems such as variable valve timing ( VVT ) with variable length intake manifold ( VLIM ) or acoustic controlled consumption system ( ACIS ) . A high public presentation fumes gas recirculation valve ( EGR ) will about surely be required to cut down the high N oxides ( NOx ) emanations which will ensue from firing extremist thin mixtures.
Conventional fuel injection engines could shoot fuel throughout the 4 shot sequence, as the injector injects fuel onto the dorsum of a closed valve. Earlier direct injection engines, where the injector injects fuel straight into the cylinder, were limited to the initiation shot of the Piston.
As the RPM additions, the clip available to shoot fuel lessenings. Newer GDI systems have sufficient fuel force per unit area to shoot more than one time during a individual rhythm. Fuel injection takes topographic point in two stages. During the consumption shot, some sum of fuel is “ pre-injected ” into the burning chamber which cools the entrance air, therefore bettering volumetric efficiency and guaranting an even fuel/air mixture within the burning chamber. Main injection takes topographic point as the Piston approaches top dead Centre on the compaction shot, shortly before ignition.
The benefits of direct injection are even more marked in two-stroke engines, because it eliminates much of the pollution that their conventional design causes. In conventional two-strokes, the fumes and intake ports are both unfastened at the same clip, at the underside of the Piston shot. A big part of the fuel/air mixture come ining the cylinder from the crankcase through the consumption ports goes straight out, unburned, through the exhaust port. With direct injection, merely air comes from the crankcase, and fuel is non injected until the Piston rises and all ports are closed.
What is HCCI?
HCCI is an alternate piston-engine burning procedure that can supply efficiencies as high ascompression-ignition, direct-injection ( CIDI ) engines ( an advanced version of the commonly known Diesel engine ) while, unlike CIDI engines, bring forthing ultra-low oxides of N ( NOx ) and particulate affair ( PM ) emanations. HCCI engines operate on the rule of holding a dilute, premixed charge that reacts and Burnss volumetrically throughout the cylinder as it is compressed by the Piston. In some respects, HCCI incorporates the best characteristics of both spark ignition ( SI ) and compaction ignition ( CI ) , as shown in Figure 1. As in an SI engine, the charge is good assorted, which minimizes particulate emanations, and as in a CIDI engine, the charge is compaction ignited
and has no choking losingss, which leads to high efficiency. However, unlike either of these
conventional engines, the burning occurs at the same time throughout the volume instead than in a fire forepart. This of import property of HCCI allows burning to happen at much lower temperatures, dramatically cut downing engine-out emanations of NOx.
Most engines using HCCI to day of the month hold double manner burning systems in which traditional SI or CI burning is used for operating conditions where HCCI operation is more hard.
Typically, the engine is cold-started as an SI or CIDI engine, so switched to HCCI manner for idle and low- to mid-load operation to obtain the benefits of HCCI in this government, which comprises a big part of typical automotive drive rhythms. For high-load operation, the engine would once more be switched to SI or CIDI operation. Research attempts are afoot to widen the scope of HCCI operation, as discussed in the organic structure of this study.
What are the Advantages of HCCI?
The advantages of HCCI are legion and depend on the burning system to which it is
compared. Relative to SI gasolene engines, HCCI engines are more efficient, nearing the
efficiency of a CIDI engine. This improved efficiency consequences from three beginnings: the riddance of restricting losingss, the usage of high compaction ratios ( similar to a CIDI engine ) , and a shorter burning continuance ( since it is non necessary for a fire to propagate across the cylinder ) . HCCI engines besides have lower engine-out NOx than SI engines. Although tripartite accelerators are equal for taking NOx from current-technology SI engine fumes, low NOx is an of import advantage comparative to spark-ignition, direct-injection ( SIDI ) engineering, which is being considered for future SI engines.
Relative to CIDI engines, HCCI engines have well lower emanations of PM and NOx.
( Emissions of PM and NOx are the major hindrances to CIDI engines run intoing future emanations criterions and are the focal point of extended current research. ) The low emanations of PM and NOx in HCCI engines are a consequence of the dilute homogenous air and fuel mixture in add-on to low burning temperatures. The charge in an HCCI engine may be made dilute by being really thin, by stratification, by utilizing exhaust gas recirculation ( EGR ) , or some combination of these. Because fire extension is non required, dilution degrees can be much higher than the degrees tolerated by either SI or CIDI engines. Combustion is induced throughout the charge volume by compaction heating due to the Piston gesture, and it will happen in about any fuel/air/exhaust-gas mixture once the 800 to 1100 K ignition temperature ( depending on the type of fuel ) is reached. In contrast, in typical CI engines, minimal fire temperatures are 1900 to 2100 K, high plenty to do unacceptable degrees of NOx. Additionally, the burning continuance in HCCI engines is much shorter than in CIDI engines since it is non limited by the rate of fuel/air commixture. This shorter burning continuance gives the HCCI engine an efficiency advantage. Finally, HCCI engines may be lower cost than CIDI engines since they would probably utilize lower-pressure fuel-injection equipment.
Another advantage of HCCI burning is its fuel-flexibility. HCCI operation has been shown utilizing a broad scope of fuels. Gasoline is peculiarly good suited for HCCI operation. Highly efficient CIDI engines, on the other manus, can non run on gasolene due to its low cetane figure. With successful R & A ; D, HCCI engines might be commercialized in light-duty rider vehicles by 2010, and by 2015 every bit much as a half-million barrels of oil per twenty-four hours may be saved. Trials have besides shown that under optimized conditions HCCI burning can be really quotable, ensuing in smooth engine operation. The emanation control systems for HCCI engines have the possible to be less dearly-won and less dependent on scarce cherished metals than either SI or CIDI engines.
HCCI is potentially applicable to both car and heavy truck engines. In fact, it could be scaled to virtually every size-class of transit engines from little bike to big ship engines. HCCI is besides applicable to piston engines used outside the transit sector such as those used for electrical power coevals and grapevine pumping.
Consequences Using Different Fuels
One of the advantages of HCCI burning is its intrinsic fuel flexibleness. HCCI burning has small sensitiveness to fuel features such as prurience and laminar fire velocity. Fuels with any octane or cetane figure can be burned, although the operating conditions must be adjusted to suit different fuels, which can impact efficiency, as discussed below. An HCCI engine with VCR or VVT could, in rule, run on any hydrocarbon or intoxicant liquid fuel, every bit long as the fuel is vaporized and assorted with the air before ignition.
The literature shows that HCCI has been achieved with multiple fuels. The chief fuels that have been used are gasoline, diesel fuel, propane, natural gas, and single- and dual-component mixtures of the gasolene and Diesel primary mention fuels ( iso-octane and n-heptane, severally ) . The pertinence of these fuels to HCCI engines is discussed below. Other fuels ( methyl alcohol, ethyl alcohol, propanone ) have besides been tried in experiments, but with inconclusive consequences.
Gasoline: Gasoline has multiple advantages as an HCCI fuel. Gasoline besides has a high octane figure ( 87 to 92 in the U.S. and up to 98 in Europe ) , which allows the usage of moderately high compaction ratios in HCCI engines. Actual compaction ratios for gasoline-fueled HCCI engine informations vary from 12:1 to 21:1 depending on the fuel octane figure, intake air temperature, and the specific engine used ( which may impact the sum of hot residuary of course retained ) . This compression-ratio scope allows gasoline-fueled HCCI engines to accomplish comparatively high thermic efficiencies ( in the scope of diesel-fueled CIDI engine efficiencies ) . A possible drawback to higher compaction ratios is that the engine design must suit the comparatively high cylinder force per unit areas that can ensue, peculiarly at high engine tonss ( see treatment in Section V B ) . Extra advantages of gasolene include easy vaporization, simple mixture readying, and a omnipresent refueling substructure.
Diesel Fuel: Diesel fuel autoignites quickly at comparatively low temperatures but is hard to
evaporate. To obtain diesel-fuel HCCI burning, the air-fuel mixture must be heated
well to vaporize the fuel. The compaction ratio of the engine must be really low ( 8:1
or lower ) to obtain satisfactory burning, which consequences in a low engine efficiency.
Alternatively, the fuel can be injected in-cylinder, but without air preheating, temperatures are non sufficiently high for diesel-fuel vaporisation until good up the compaction shot. This scheme frequently consequences in uncomplete fuel vaporisation and hapless mixture readying, which can take to particulate affair and NOx emanations
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Fundamentalss of internal burning engines. writer: H.N.gupta
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