Document 7OLqM7vkBp50dn8ngJb24ORD8

ratios, give high efficiency on relatively low-cost nonhazardous fuel, and need no ignition system. Maximum Pro#tore. On the other hand, engines operating ei lower compression ratios usually cost less to manufacture. Strictly speaking, it is the pressure reached after firing rather than com* pression pressure that U important in this connection. A pressure rise al ways follows firing; how much depends on the way the fuel bums. When fuelair mixture is compressed and ignited by a spark, combustion Is fast, practi cally an explosion, and pressure rises rapidly. When fuel is injected into com pressed air, rate of burning can be con trolled to some extent and pressure rise is less rapid. Because most spark-ignition engines operate at fairly tow compression pres sures, rapid pressure rise after firing doesn't usually raise maximum pres sure above 400-500 psi. Low-compression pressures and slow pressure rise of surface ignition engines give maxi mum pressures of about 230 psi. Al though diesel compression pressures are high, slow rote of pressure rise holds maximum pressure down to about 600-1200 psi, large low-speed engines showing the lower figures. Low maximum pressure means less tress in engine frame and parts and lower loads on bearings. This permits relatively simple design end lower manufacturing costs. Presence or ab sence of a high-pressure Injection systern also influences first cost There are many applications where Invest ment cost is more important than oper ating economy. Oes-Oiaiefs, OuehFoof. Considerable Interest attaches to recent development of high-compression engines for burn ing gas. In the first of these, eir only Is compressed. Oas Is injected under about 1100-psi pressure. To stabilise the combustion, a small quantity of "pilot" oil is also injected. Diesel effi ciencies obtain when burning gas; con version to oil can be effected in a mat ter of hours. The so-called dual-fuel engine oper ates at diesel pressures, with diesel efficiencies, can switch from gas to oil or oil to gas under load, and can bum combinations of oil end gas. It appa rently violates all the rules by mixing fuel and oir before compression and then raising the mixture to high pres sures. Preignltion does not occur; in fact, burning is started and maintained by injecting pilot oil into the heated mixture. Difference in fuel-air ratios between these engines end conventional gas ond gasoline engines probably accounts for differences in Ignition behavior. Oas engines operate with a nearly "perfect" 66 (202) 2-STROKE AND 4-STROKE CYClf l Art INTAKE VUH fnltt * l COMMISSION 4"$TROKE CYCU-ONE POWER STROKE TO TWO FUU aster1 iv,fturnfreefctm fT* Mi-riniMt I I i/I rronkett*. t# bt comprtt*. I I i;jj: 1if ii nr- 2-STROKE CYCU-ONE POWER STROKE TO EACH EUU. REVO WHAT COMPRESSION RATIO MEANS A 6:1 Compression 1 1 1 1 ' * u L. Oamprttalon Ratio mixture, readily ignited, explosive in its burning. The dual-fuel engine, being essentially o diesel, operates .with high excess air, or a "lean" mixture. Bven ot high temperatures, such a mixture does not self-ignite in the short time available. (For a full discussion see Power, May 1945, pp 64-70.) Cycles. Some internal-combustion engines operate on the 4.froke cycle, others on the 2-sfroka cycle. This sim ply means that, in the first cate, four strokes, or two complete are needed for the full cycle of i| compression, expansion ond In the second case, the some completed in two strokes, or o plete revolution. In other words. 2-cycle engine fire* twice o the 4-cycle. Diagrams above show the sW' of events of these two cycles. Not* In 2-cycle engines to blow the ** gas out of the cylinder and fill .PQWEt flflTIAL DIESEL ELEMENTS AND WHAT THEY DO ajsii of typical verllesl 4-eycle engine Kaodified end simplified to show (he basic frelesrly. On bedplate reus ihe /rame. riel the cylinder finer#. The cylinder head _ fttoj 0f the cylinder, the piiton form# e>'Mnd" h",d "\ lutl noilfo. infer tnd eifieurl valves, ond mottling the valve ports lo Inlet snd niloidt. flolh cylinder and hestl are jackets In which cooling water TMm Me* -- inxxjf0^---------- 4 W&MCiint rod join# the piitoo and crank "Topper end eerrie# the icmtpin bearing ier tnd the cranfcpin bearing. The era'nkI in the main Acaringi, supported by the fiie enclosed spseO' formed by frame ond J|ow the cylinders, through which the [t runs, Is esited the crankcase. f\#t pump . pnbbaft drives the camshaft, by chain or . ni scluste push rods which, in turn, r irmt and the respective valves. .The which tupplies high-pressure fuel to j ii utuslly camshaft-driven. _j shown is typical, hut location of npsrti varies front engine lo engine, and is' .shown appear in all engines. , m Oo. The functions of the pens.can as follows: The cylinder heed, liner form* the combustion space. In which the eempressed snd Into which the /uef-' TTsyurm (pumps, fuel iSnea, noisles) dts- ''ijftttered amount of. fuel, property atom- id eombuttion. .-elfarco produced by burning fuel drives -' ^`dowfi end, through the connecting rod, xiergy to the crankshaft Valve mechanism land..drive, puth rod*,' rocker arms) jnd times the movniicnl of the vsKcs con- iw of fresh sir into the cylinder and diw , ^yomhunion products. .'* , s seen that engine parti break down into roups: < 1) structural parts-.bedplate,' jg'ra, heads .(2) major moving ports7-piitop, g Yods, crankshaft, and their respective _ (J) srrsngententi for getting air in', and but w valves, valve mechanism, manifolds,' , mg!*>nd supercharging systems and (4) .fuel-, ^tytiem -- pumps, nottles, control devices. Bhrts' will lie covered in `greater .detail-In . {that follow. -7 l Fir. air at a pressure slightly * shaoipheric la needed. This is r. In the diagram, auader pressure is obtained by using g/Cunkcase end underside of the an air compressor. This is ..crankcase scavenging; other 1 f scavenging, end superV> which should not be confused ,f* described later. r Arroupameot. In the com* of internal.combustion en- gine, cylinders are arranged vertically, in line. Number of cylinders ranges from one to 10, normolty. Engines are also built with horizontal cylinders, usually single- or twin-cylinder. The compeet "V"design is frequently employed, usually in B-, 12- or 16-cyl inder combinations. If the V is opened out to 90 deg, we have an angle type. Where a fiat engine is desired, the V may be opened out to 160 deg. yielding anoppoaed-cylinderengine. This should not be confused with the oppoeedpiston engine, shown on p 89, in which two pistons operate in what is esien- _ tielly a single cylinder, with a combus tion chamber in the center between the pistons end a crankshaft at each end. Essential elements of a. vertical diesel are illustrated above; same parts in different arrangement comprise en gines of other types. Next page shows typical auxiliaries serving the main en gine in a stationary plant ' AprfltNI (2001 67 i'm