cee11-fa08-mt2-Harley-soln

cee11-fa08-mt2-Harley-soln - Page E Midterm Exam CEE 11 m...

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Unformatted text preview: Page E Midterm Exam CEE 11 m Engineered Systems & Sustainability University of California at Berkeley Fall Semester 2008 NAME: So ow; Instructions: answer the questions that follow directly on these pages in the spaces provided. Use the back of the page if you need more room for your answer. if you believe there is insufficient information provided to answer a question completely, state reasonable additional assumptions and proceed from there. The exam is closed—book, but see last page for aid sheet. You may use a CEIiCLilfltOI‘. Please write your name in the space provided above! Time: 50 minutes Question SCORE: OUT OF: 1 8 2 S 3 7 Total 20 l. ETHANOL COMBUSTION (21) Suppose the molar ratio of CO to C03, Q i a/b 1* 0.3 is measured in the exhaust plume of a passing car that is burning pure ethanol as fuel. Calculate the air—fuel mass ratio for these conditions. For fuel—rich conditions, the combustion stoichiometry can be approximated as follows: cagcngoa + m [ o3 +4512] ~—z- aCO+b (:02 +3 ago+4m N3 02 z 6%., 1) :fwla e: ctr—05319 0"” {35:2 Lil’s»qu a=-0344é I) 0‘;ng iacLQez/me ': a‘i'Zlo ‘m “:— a+2l9 +2 2 2.77 2, Owl!” [A’Qfl fix/3'! 0 ma _ 21.777 1 Mel 0.2 Jr- U ml ML) x Wig/ad Mp ; wwl miwl >< 46 MM” ii Page 3 (1)) Estimate the percentage increase in fuel consumption for conditions ofpart (a), relative to the idea} case of complete combustion. See next page for thermodynamic data. Juan, 3' ‘w‘fle WWW CWQCWEW 30E: ‘ £7“ (6"); MM CQ’l/L‘L/b’M/D’i’f‘m M wow : 20 .— “KL-+3 We qr, Co a Nme mi w: {l4 énluum (L' 5/ “E00 :1 X. 5AM“ :3 92831997 moi Sim Leo 3/;th 8%“ LHQ: “‘ Agaov a Macowéénwo I; 28330037W1 MWLD ' 2:3 9M| 9-3 MW; 5 $10 [:IA ( Page 4 2. ETHANOL COMBUSTION The lower heating vaEue for ethanol is 30 M g"[. Assuming that air and fuel enter at T9 = 298 K, calculate the adiabatic flame temperature for ethanol combustion, assuming the following stoichiomctry: CH3CH20H + 3.3 [02 ‘3‘ 4 N3 ] “'3’ 2 C02 "i" 3 H30 + 0.3 02 +132 N2 _ 11hr (1 moi“) 0P 0 moi“ K“) «394 000 co () —1 10 700 H30 (g) ~242 000 41 .- - .. I (am AK“ “’ gojfi A #bwgf :“l 38 K10; ‘j WWI WWI H K: O as» (9 TY Page 5 3. IMPROVING FUEL ECONOMY According to the Federal Highway Administration (FHWA) as of 2005, the totai amount of diesel fuel consumed by heavy trucks in the U.S. was 92 billion liters, the total amount of driving was 230 billion km, and the total number of heavy trucks was about 2 million. Here are some approximate values for iieavy»dnty trucks: Drag coefficient, (39 = 0.9 (for tractor-trailer combinations) Truck frontal area, Arm 1?. 1112 Air density, 93 m 1.2 kg m”3 Roliing resistance coefficient, CR = 0.0} Truck + cargo mass, in W 25 000 kg (a) Calculate the implied efficiency of diesel engines based on the above data (efficiency 2 total engine work done divided by total fuel energy consumed). The heating value and density ol’diescl fuei are 45 Nil/kg and 0.84 kg/L, respectively. Assume fl truck travel takes place on level highways at a constant speed of 90 kin/b, transmission efficiency @9036, and neglect accessory/air conditioning loads. v.2 iooOw: x. [ix v: ZCM/g Lx New 9600; ‘r‘fiS 1". W la axed—(you? Q t: : Qag~ON+¥om;\/: GS‘OONJ C m (Mime ' i-eiU $4.9 d}: ngxipi/Cim W l \ , , - \/ U" -_—, ..v’ [Citing +— CDAIF J 2:” «l r 6 I, T h _ , t ?I d Axilo ' glar- ooh. L ‘F Pint ' gene“ 3 n: ,M r. l a f,__ 2 2: 393%” J‘ 0,8; t. ,.‘i‘ ,- nix , Ea"- W-L-HV: ‘lm Hawaiian; Mice-thu; by r: 'ri lop—j- Caz/3e m E _ ' . O swun- t . W ‘ A (Lchw—p F «EA/Lac Page 6 (13) Assuming a price of $1 per Eiter (about $4 per gailon) for diesel fuei, what would be the fuel cost savings per truck if we could reduce CD from 0.9 to 0.8 through use of wind deflectors on top of tractor cabs and simiiar measures. 2.. m . . A : ¥§ON AFR/2 _" AC0 '6 9. r 8 [0 Ag -_; (Afimfivt yoNx/ngmm — 5,3X/0 LT M 6‘ e 0‘ I {om It 5gp: AE : 9'8fo J (QM? 3— 00d 8‘ m‘ " '"‘ . (TL “V I A57: A $3 w mm “C” LHV >~'— fl: . . =~ lzZfilC’ 7 x 1L L. H 41C)- “3?. \l “3 {mp mwf mama/Egg aw SW (10+ 544 W Cg vamfl) [W66 haw/AA m3" 000 a “Jump? vaj d/h Vii/j . ...
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This note was uploaded on 12/01/2011 for the course CE 13972 taught by Professor Chow during the Spring '09 term at Berkeley.

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cee11-fa08-mt2-Harley-soln - Page E Midterm Exam CEE 11 m...

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