School of Engineering, Discipline of Mechanical Engineering
Super Eta Engine Analysis and Report Dynamics II Joel Forbes – Harper 12/14/2012
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Super Eta Engine
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Abstract This report is concerned with the BMW Super Eta engine. It ais to deterine if using the original Eta connecting rods o!er the connecting rods produced for the ".#i series BMW engine has any significant changes to the Super Eta$s running. The iportance of the choice of conrod in the Super Eta, while seeingly negligi%le, could potentially affect the engines o!erall power output and lifespan. This report aied to in!estigate the e&tent of ipact that using the shorter original eta conrods has on the Super Eta, o!er the con!entionally preferred ".#i conrod. Through 'ineatic and 'inetic analysis of the Super Eta with !aried conrod length, the report confired con!entional wisdo that the original eta conrod of length ()* cause greater loading on the +ournal %earing, the gudgeon pin and the cylinder wall, as well as resulting in a greater piston acceleration, while the longer rod resulted in saller loading. Although there is a nota%le difference %etween the conrods in ters of the resulting acceleration of the piston, as well as the loadings on the gudgeon pin and +ournal %earing, the difference is negligi%le. The difference in conrod length will result in no noticea%le increases of wear on parts or increases in perforance. It is this report$s recoendation that the use of the original Eta conrods is accepta%le and e!en prefera%le in ters of cost and a!aila%ility. There is a significant difference %etween the conrods in ters of the resulting acceleration of the piston, as well as the loadings on the gudgeon pin and +ournal %earing. The ipact of using the original eta conrod is such that it will ad!ersely affect the engine$s running through increased wear on the piston, conrod and cran'shaft, increasing the li'elihood of engine failure. It is this report$s recoendation that the ".#i conrod is a ore accepta%le and ore !ia%le option, e!en with liited a!alia%lilty of the parts. negligi%le.
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Super Eta Engine
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Intro!ction i!en the worlds e!er shrin'ing supply of petroleu fuel products, it is of particular iportance that the engineering of autoo%iles reflect a need to conser!e fuel. The trend in the industry has %een toward fuel efficiency since the earl y (-*$s, and has intensified since then as the glo%e %ecoes ore conscious of its ecological footprint. It is especially iportant to note howe!er, that the challenge of designing efficient engines coes not +ust fro lowering consuption and waste, %ut also fro ensuring an accepta%le and copetiti!e le!el of power output can %e o%tained fro the engine. This pro%le is particularly apparent in the design of the Super Eta engine. The Super Eta is an offshoot of the Eta engine ade %y BMW in the eighties, which focused on fuel efficiency. While the Eta engine achie!ed fuel efficiency, with this cae a trade off of outright power. As such, the Super Eta aied to aintain the original Eta$s efficiency while producing significantly ore power, effecti!ely %alancing the drop in fuel consuption with a %oosted power output. In the Super eta, there is a choice to %e ade on the type of conrod used/ a ()* long one fro the original Eta, or a longer ()# conrod fro the ".#i engine. While %oth conrods wor' in the engine, there is liited 'nowledge on the o!erall effects the use of conrod has on the Super Eta. To a!oid negating the effort put into %alancing the fuel econoy with power output, it is therefore iportant to fully e&plore the effects that the choice of conrod has on the engine$s perforance and longe!ity. The pro%le in particular concerns itself with deterining the loadings on iportant coponents of the engine, as well as the resulting acceleration of the piston associated with each conrod. The data recorded for %oth conrods ust then %e copared to highlight any significant differences, and the effects of these differences e!aluated in order t o 0uantitati!ely conclude if there are any nota%le ad!erse ipacts fro using a particular conrod. This will %e achie!ed through pro%les of 'ineatics associated with idealised rigid %odies, as well as the 'inetics of a echanical syste. 1ro here, a coputer siulation will %e %uilt to odel profiles of significant properties of the syste for ease of coparison.
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Super Eta Engine
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Analysis o" t#e system Analysis of the syste was perfored largely using odel %ased representations of the coponents. The cran'2conrod2piston asse%ly was pro!ided as a detailed diagra of a single piston and conrod attached to the cran'shaft, seen in figure (.
Figure 1 !etaile" "iagra# of engine asse#$ly% along with relevant infor#ation for varie" conro"& 1or the purposes of further analysis, the a%o!e diagra was siplified to a uch ore copact odel, pictured in 1igure ". This allowed for a uch clearer approach to calculation and o%ser!ation of the syste. 3alue sy%ols and 'ey geoetrical points are consistent in figures ( and ". Two !alues, 4 5theta6 and 7 5phi6 ha!e %een added to trac' the angular displaceent of %oth the conrod and cran'throw. It can %e o%ser!ed through siple trigonoetric relation that8
It was stipulated that all analysis was to %e ta'en at the a&iu designed re!olution rate, 9*** R:M. 1or all calculation purposes this was Figure ' ("ealise" syste# use" con!erted into radians per second, and interpreted as the angular in )ine#atic analysis !elocity of the cran'shaft AB, denoted ; a%8 9*** re!<in = 9*** re!<in & "> radian
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Super Eta Engine ;a% = 9)).*))
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rad
This eans that the syste undergoes a single cycle after a specific tie, denoted as @T$, where T is8 T= ( < fre0uency = (< 59***
Simplifcations o the model • • • • • • •
o & displaceent of the piston Rigid %odies Energy ass, oentu all conser!ed 1rictionless piston o!eents o energy loss due to heat at +oints o forces due to co%ustion Assue 4 * ;a%+t
It was at this point that 'ineatics was introduced to deterine 'ey !alues for the syste.
$inematics Determination of Piston properties
1ro figure one, and fro the e0uation for the !elocity of a rigid lin'8
Siilarly, the !elocity of point C could %e e&presses as8
sing our pre!ious assuption that there is no o!eent of the piston in the & direction, we can put all of 3c$s i coponents e0ual to ero, put 7 in ters of 4 and use our assuption that 4 = ;a%Ft
To get the angular acceleration of lin' BC 5the conrod6, the deri!ati!e of ; %c was ta'en8
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Super Eta Engine
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oting that the piston o!es only up and down, we can consider the G coponents of 3c to %e the !elocity of the piston, then su% in the e0uation for ; %c .
A siilar e&pression for the acceleration of the piston can %e o%tained %y differentiating 3c.
As can %e seen, the !alues R, ,a$ an" t are the sa#e for $oth conro"s use"% $ut the
results of all the a$ove vary with -&
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