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BAB I PENDAHULUAN
1.1 Latar Belakang
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1.2 Tujuan Praktikum
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BAB II TINJAUAN PUSTAKA
2.1 Pengertian Motor Bakar
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2.2 Prinsip Kerja Motor Bakar Torak
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2.2.1 Prinsip Kerja Motor Bakar Torak Berdasarkan Langkah Kerja
2.2.1.1 Motor Bakar Torak 2 Langkah
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2.2.1.2 Motor Bakar Torak 4 Langkah
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2.2.2 Prinsip Kerja Motor Bakar Torak Berdasarkan Sistem Penyalaan
2.2.2.1 Motor Bakar Diesel (Compression Ignition Engine)
A. Pengertian
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B. Siklus Termodinamika
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C. Rasio Kompresi
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2.2.2.2 Motor Bakar Bensin (Spark Ignition Engine)
A. Pengertian
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B. Siklus Termodinamika
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C. Rasio Kompresi
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2.3 Karakteristik Bahan Bakar
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2.3.1 Flash Point
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2.3.2 Fire Point
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2.3.3 Auto-Ignition Point
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2.3.4 Viskositas
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2.3.5 Densitas
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2.3.6 Nilai Kalor
A. High Heating Value (HHV)
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B. Low Heating Value (LHV)
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2.3.7 Octane Number
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2.3.8 Cetane Number
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2.4 Karakteristik Kinerja Motor Bakar
2.4.1 Indikator Kinerja Motor Bakar
A. Torsi
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B. Daya Indikatif
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C. Daya Efektif
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D. Daya Mekanis
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E. Mean Effective Pressure
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F. Specific Fuel Consumption
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G. Efisiensi
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H. Air-Fuel Ratio dan Fuel-Air Ratio
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2.4.2 Indikator Operasional Motor Bakar
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A. Bukaan Katup (Throttle)
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B. Beban Mesin
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2.5 Hubungan Indikator Operasional terhadap Indikator Kinerja
2.5.1 Motor Bakar Diesel
2.5.1.1 Grafik Hubungan Putaran terhadap Torsi, Daya Efektif, dan SFC
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A. Grafik Hubungan Putaran terhadap Torsi
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B. Grafik Hubungan Putaran terhadap Daya Efektif
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C. Grafik Hubungan Putaran terhadap SFC
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2.5.1.2 Grafik Hubungan Putaran terhadap Daya Mekanis, Daya Indikatif,
dan MEP
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A. Grafik Hubungan Putaran terhadap Daya Mekanis
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B. Grafik Hubungan Putaran terhadap Daya Indikatif
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C. Grafik Hubungan Putaran terhadap MEP
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2.5.2 Motor Bakar Bensin
2.5.2.1 Grafik Hubungan Putaran terhadap Torsi, Daya Efektif, dan SFC
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A. Grafik Hubungan Putaran terhadap Torsi
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B. Grafik Hubungan Putaran terhadap Daya Efektif
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C. Grafik Hubungan Putaran terhadap SFC
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2.6 Governor Kecepatan
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2.6.1 Karakteristik Governor
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2.6.2 Tipe Governor
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2.7 Orsat Apparatus
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2.8 Diagram Sankey
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2.9 Teknologi Motor Bakar Terbaru
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2.9.1 Definisi
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2.9.2 Tujuan
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2.9.3 Prinsip Kerja
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2.9.4 Kelebihan dan Kekurangan
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2.9.5 Aplikasi dan Cara Perawatan
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BAB III METODE PENELITIAN
3.1 Waktu dan Tempat
Waktu :
Jam :
Tempat : Laboratorium Motor Bakar Teknik Mesin Universitas Brwaijaya
3.2 Pelaksanaan Praktikum
3.2.1 Instalasi Percobaaan Motor Diesel
Peralatan praktikum yang tersedia adalah instalasi percobaan (test rig)
lengkap, yang terdiri dari :
v Instalasi Percobaan Motor Diesel
v Unit Motor Diesel sebagai objek percobaan / penelitian.
v Instrumen pengukur berbagai variabel yang diperlukan (barometer,
higrometer, aeorometer, orsat apparatus).
v Peralatan bantu seperti instalasi air pendingin dan penyaluran gas buang.
Unit motor bakar yang digunakan adalah motor diesel dengan 4 silinder,
dengan spesifikasi sebagai berikut :
o Siklus : 4 langkah
o Jumlah silinder : 4
o Volume langkah torak total : 2164 cm3
o Diameter silinder : 83 mm
o Panjang langkah torak : 100 mm
o Perbandingan kompresi : 22 : 1
o Bahan bakar : Dexlite
o Pendingin : Air
o Daya Poros : 47 BHP / 3200 rpm
o Merk : Nissan, Tokyo Co.Ltd.
o Model : DWE – 47 – 50 – HS – AV
o Negara pembuat : Jepang
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Gambar 3.1 Skema Instalasi Motor Diesel Sumber: Laboratorium Motor Bakar Jurusan Mesin Universitas Brawijaya (2019)
3.2.2 Alat Ukur dan Fungsinya
Alat ukur serta fungsinya yang digunakan saat praktikum adalah sebagai
berikut :
a. Orsat apparatus
Digunakan untuk mengukur dan menganalisa gas buang (%).
Gambar 3.2 Orsat apparatus Sumber: Laboratorium Motor Bakar Jurusan Mesin Universitas Brawijaya (2019)
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b. Barometer
Digunakan untuk mengukur tekanan atmosfer (mmHg).
Gambar 3.3 Barometer Sumber: Laboratorium Motor Bakar Jurusan Mesin Universitas Brawijaya (2019)
c. Aerometer
Digunakan untuk mengukur massa jenis bahan bakar (kg/m3).
Gambar 3.4 Aerometer Sumber: Laboratorium Motor Bakar Jurusan Mesin Universitas Brawijaya (2019)
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d. Flash Point
Digunakan untuk mengetahui titik nyala api suatu bahan bakar (oC).
Gambar 3.5 Flash Point Sumber: Laboratorium Motor Bakar Jurusan Mesin Universitas Brawijaya (2019)
e. Diesel Engine Test Bed
Digunakan untuk mengetahui parameter-parameter yang menunjukkan
karakteristik motor bakar.
Gambar 3.6 Diesel Engine Test Bed Sumber: Laboratorium Motor Bakar Jurusan Mesin Universitas Brawijaya (2019)
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f. Stopwatch
Digunakan untuk mengetahui waktu konsumsi bahan bakar (s)
Gambar 3.7 Stopwatch Sumber: Laboratorium Motor Bakar Jurusan Mesin Universitas Brawijaya (2019)
g. Hygrometer
Digunakan untuk mengukur kelembaban relatif udara (%).
Gambar 3.8 Hygrometer Sumber: Laboratorium Motor Bakar Jurusan Mesin Universitas Brawijaya (2019)
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h. Dynamometer
Digunakan untuk mengetahui gaya pembebanan pada poros (Kg).
Gambar 3.9 Dynamometer Sumber: Laboratorium Motor Bakar Jurusan Mesin Universitas Brawijaya (2019)
i. Flowmeter air pendinginan
Digunakan untuk mengukur debit aliran air pendinginan (liter/jam).
Gambar 3.11 Flowmeter air pendinginan Sumber: Laboratorium Motor Bakar Jurusan Mesin Universitas Brawijaya (2019)
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j. Flowmeter Bahan Bakar
Digunakan untuk mengukur konsumsi bahan bakar (ml).
Gambar 3.12 Flowmeter bahan bakar Sumber: Laboratorium Motor Bakar Jurusan Mesin Universitas Brawijaya (2019)
k. Manometer
Digunakan untuk mengukur perbedaan tekanan dalam system (mmH2O).
Gambar 3.13 Manometer Sumber: Laboratorium Motor Bakar Jurusan Mesin Universitas Brawijaya (2019)
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l. Viscometer
Digunakan untuk mengukur viskositas fluida (η).
Gambar 3.14 Viscometer Sumber: Laboratorium Motor Bakar Jurusan Mesin Universitas Brawijaya (2019)
m. Bomb calorimeter
Digunakan untuk mengetahui kalor bahan bakar (Kcal/Kg)
Gambar 3.15 Bomb Calorimeter Sumber: Laboratorium Motor Bakar Jurusan Mesin Universitas Brawijaya (2019)
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n. STARGAS 898
Digunakan untuk menganalisis kandungan gas buang.
Gambar 3.16 STARGAS 898 Sumber: Laboratorium Motor Bakar Jurusan Mesin Universitas Brawijaya (2019)
3.3 Prosedur Pengambilan Data Praktikum
Setiap kelompok praktikum melaksanakan sendiri semua proses pengujian
dan pengambilan data yang diperlukan untuk memenuhi tujuan praktikum di atas.
Dalam melaksanakan proses pengujian tersebut, mahasiswa harus mengikuti
semua aturan dan tata tertib yang berlaku di laboratorium dan mengikuti semua
petunjuk asisten laboratorium yang bertugas.
Metode percobaan dengan variasi putaran, parameter yang diukur adalah :
1. Gaya Pengereman
2. Perbedaan Tekanan Masuk dan Keluar Nozzle
3. Kelembapan Udara
4. Suhu Gas Buang
5. Suhu Air Masuk dan Air keluar
6. Debit Bahan Bakar
7. Kandungan Gas Buang
8. Tekanan Udara
3.3.1 Prosedur Pengujian Motor Bakar
1. Persiapan Sebelum Mesin Beroperasi
a. Menyalakan pompa pengisi untuk mengisi air dalam tangki sampai level air
mencapai tinggi aman dan menyalakan cooling tower
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b. Membuka kran air pada pipa-pipa yang mengalirkan air ke mesin dan ke
dinamometer.
c. Mengatur debit air yang mengalir pada flowmeter pada debit tertentu dengan
mengatur bukaan kran pada flowmeter.
d. Menekan switch power untuk menghidupkan alat-alat ukur.
e. Menghidupkan alarm air pendinginan yang akan memberitahu jika terjadi
overheating dan level air kurang.
f. Menyalakan dinamo power control dan atur kondisi poros mesin dalam
keadaan tanpa beban.
2. Cara Menghidupkan Mesin
a. Mengatur bukaan throttle sesuai yang diinginkan
b. Setelah semua persiapan di atas dipenuhi, menyalakan kunci kontak pada
posisi memanaskan mesin terlebih dahulu sampai indikator glow signal
menyala.
c. Memutar posisi kunci ke posisi START sambil mengurangi pembebanan
pada poros.
d. Setelah mesin menyala, biarkan mesin beroperasi beberapa saat untuk
menstabilkan kondisi mesin.
3. Cara Mengambil Data
a. Atur putaran mesin (rpm) dengan mengatur pembebanan pada dinamometer
sampai mendapatkan putaran yang diinginkan.
b. Tunggu kondisi mesin stabil kemudian lakukan pengambilan data yang
diperlukan.
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3.3.2 Prosedur Penggunaan Orsat Apparatus
Gambar 3.17 Orsat Apparatus Sumber: Laboratorium Motor Bakar Jurusan Mesin Universitas Brawijaya (2019)
Cara penggunaan Orsat Apparatus :
1. Set ketiga tabung I, II, III pada ketinggian tertentu dengan membuka keran A,
B, C dan mengatur tinggi larutan pada tabung I, II, III dengan menaik –
turunkan gelas B, kemudian tutup keran A, B, C setelah didapatkan tinggi
yang diinginkan. Posisi ini ditetapkan sebagai titik acuan.
2. Naikkan air yang ada pada tabung ukur C sampai ketinggian air mencapai 50
ml dengan cara membuka keran H dengan menaikkan gelas B. Setelah
didapatkan tinggi yang diinginkan, tutuplah kembali keran H.
3. Ambil gas buang dari saluran gas buang untuk diukur, salurkan melalui
selang yang dimasukkan ke dalam pipa H.
4. Buka keran H sehingga gas buang akan masuk dan mengakibatkan tinggi air
yang ada di tabung ukur C akan berkurang.
5. Setelah tinggi air pada tabung ukur turun sebanyak 50 ml (sampai perubahan
air mencapai angka 0) tutuplah keran H dan kita sudah memasukkan volume
gas buang sebanyak 50 ml.
6. Untuk mengukur kandungan CO2 buka keran A supaya gas buang bereaksi
dengan larutan yang ada pada tabung III dengan mengangkat dan
menurunkan gelas B sebanyak 5 – 7 kali.
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7. Setelah 5 – 7 kali kembalikan posisi larutan III ke posisi acuan pada saat set
awal dan tutup keran C setelah didapatkan posisi yang diinginkan.
8. Baca kenaikan permukaan air yang ada pada tabung ukur C. Kenaikan
permukaan air merupakan volume CO2 yang ada pada 50 ml gas buang yang
kita ukur.
9. Untuk mengukur kandungan O2 dan CO ulangi langkah 6 dan langkah 7
untuk keran B dan keran A pada tabung II dan tabung I.
10. Baca kenaikan permukaan air pada tabung ukur C dengan acuan dari tinggi
permukaan air sebelumnya.
3.3.3 Prosedur Penggunaan STARGAS 898
Gambar 3.18 STARGAS 898 Sumber: Laboratorium Motor Bakar Jurusan Mesin Universitas Brawijaya (2019)
Cara Penggunaan STARGAS 898 :
1. Masukan gas probe pada pipa gas buang
2. Nyalakan STARGAS Gas Analyzer
3. Pilih fungsi MEASUREMENT pada halaman GAS ANALYSIS
4. Pilih fungsi STANDARD TEST pada halaman TEST SELECTION
5. Tekan MENU untuk menunjukkan FUNCTION BAR dalam halaman
measurement pada standard test
6. Print hasil analisis gas buang untuk percobaan pada putaran pertama.
7. Lepaskan gas probe dari pipa gas buang.
8. STARGAS Gas Analyzer berada pada kondisi Autozero
9. Ulangi dari langkah pertama untuk analisis gas pada percobaan kedua dan
selanjutnya.
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3.3.4 Rumus Perhitungan
Adapun rumus – rumus yang digunakan dalam perhitungan hasil percobaan
adalah sebagai berikut :
1. Momen Torsi
lFT ×= (kg.m) (3-1)
Dimana :
T : Torsi (kg.m)
F : besar gaya putar (kg)
L : panjang lengan dinamometer = 0,358 (m)
2. Daya Efektif
2,716nTNe ×
= (PS) (3-2)
Dimana :
n : putaran (rpm)
Ne : daya efektif (PS)
T : momen torsi (kg.m)
3. Daya Efektif dalam kondisi standard JIS
NekNeo .= (PS) (3-3)
293273749 θ+
−=
PwPak ;
PsPw .ϕ=
Dimana :
Neo : daya efektif yang dikonfersi dalam JIS (PS)
k : faktor konversi
Ne : daya efektif (PS)
Pa : tekanan atmosfir pengukuran (mmHg)
Pw : tekanan uap parsial (mmHg)
θ : rata-rata temperatur ruangan saat pengujian (°C)
ϕ : kelembamam udara (%)
Ps : Tekanan udara standar pada temperatur θ (mmHg)
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4. Mean Effective Pressure (MEP)
Pe = niVdzNeo
××
×× 45,0 ( kg/cm2 ) (3-4)
Dimana :
Pe : tekanan efektif
z : jumlah putaran poros engkol
n : putaran poros engkol (rpm)
i : langkah mesin
Vd : volume langkah (m3)
5. Fuel Consumption
10003600
××= ρtVFC (kg/jam) (3-5)
ρ dexlite = 0,836 gr/mL
Dimana :
𝐹𝐶 : Konsumsi bahan bakar (kg/jam)
𝑉 : Volume bahan bakar (ml)
𝜌 : Massa jenis bahan bakar (gr/ml)
T : Waktu konsumsi bahan bakar (s)
6. Panas Hasil Pembakaran
𝑄𝑏 = 𝐹𝐶 𝑥 𝐿𝐻𝑉 ( )Jamkcal
(3-6)
Dimana :
Qb : panas hasil pembakaran (kcal/jam)
FC : konsumsi bahan bakar (kg/jam)
LHV : Low Heating Value (kcal/kg)
7. Berat Jenis udara
( )woa
PsPaγϕ
θϕ
γγ .273273
760.. +
+×
−×=
(3-7)
Dimana :
Pa : Tekanan atmosfer pengukuran (mmHg)
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Ps : Tekanan udara standard pada temperatur tertentu (mmHg)
ϕ : Relative Humidity / Kelembapan Relatif (%)
γo : Berat jenis udara kering pada 760 mmHg
θ : Temperatur bola kering(oC)
8. Koefisien Udara
1
21
PPP −
=ε (3-8)
Dimana :
PP −1 : beda tekanan pada nozzle (mmH2O)
1P : tekanan atmosfer saat pengujian (mmHg)
ε : koefisien udara
9. Massa alir udara melalui nozzle
( )21
2
..24... PPgdGs a −= γ
πεα (kg/s) (3-9)
Dimana :
Gs : Massa alir udara melalui nozzle (kg/s)
α : Koefisien kemiringan nozzle = 0,822
ɛ : Koefisien udara
d : diameter nozzle = 0,048 m
g : Gaya gravitasi = 9,81m/s2
aγ : Berat jenis udara (kg/m3)
𝑃1 – 𝑃2 : Perbedaan tekanan pada nozzle
10. Massa Alir gas buang
3600FCGsGg += (kg/s) (3-10)
Dimana :
Gg : massa alir gas buang (kg/s)
Gs : massa alir udara melalui nozzle (kg/s)
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FC : konsumsi bahan bakar (kg/jam)
11. Panas yang terbawa gas buang
𝑄𝑒𝑔 = 𝐺𝑔.𝐶𝑝𝑔. 𝑇𝑒𝑔 − 𝑇𝑢𝑑 x 3600 (kcal/jam) (3-11)
Dimana :
Cpg : panas jenis gas buang (kcal/kg.oC)
Teg : suhu gas buang (°C)
Tud : temperatur(°C)
Gg : massa alir gas buang (kg/s)
Qeg : panas yang terbawa gas buang (kcal/jam)
12. Efisiensi kerugian dalam exhaust manifold ( gη )
%100xQbQeg
g =η (3-12)
Dimana :
gη : efisiensi kerugian (%)
Qeg : panas yang terbawa gas buang (kcal/jam)
Qb : panas hasil pembakaran (kcal/jam)
13. Kerugian Panas Pendinginan (Qw)
Qw =ρ.Ww.Cpw (Two-Twi) (kcal/jam) (3-13)
Dimana :
ρ : Massa jenis air = 1 kg/liter
Ww : debit air pendinginan (liter/jam)
Cpw : panas jenis air = 1 kcal/kg.oC
Two : temperatur air keluar (oC)
Twi : temperatur air masuk (oC)
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14. Efisiensi Kerugian Panas dalam cooling water( wη )
%100xQbQw
w =η (3-14)
Dimana :
wη : efisiensi kerugian panas (%)
Qw : kerugian panas pendinginan (kcal/jam)
Qb : panas hasil pembakaran (kcal/jam)
15. Efisiensi Thermal Efektif ( eη )
%100632××=QbNe
eη (3-15)
Dimana :
eη : efisiensi efektif (%)
Ne : daya efektif (PS)
Qb : panas hasil pembakaran (kcal/jam)
16. Efisiensi Mekanis ( fη )
( )ewgf ηηηη ++−= %100 (3-16)
Dimana :
fη : efisiensi gesekan (%)
gη : efisiensi kerugian gas buang (%)
wη : efisiensi kerugian air pendinginan (%)
eη : efisiensi efektif (%)
17. Ekuivalen daya terhadap konsumsi bahan bakar (Qf )
𝑄𝑓 = !"#.!"!"#
(PS) (3-17)
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Dimana :
LHV : Low Heating Value (kcal/kg)
FC : konsumsi bahan bakar (kg/jam)
18. Daya Mekanis
%100xQf
Nf fη= (3-18)
Dimana :
Nf : daya mekanis (PS)
fη : efisiensi gesekan (%)
Qf : kerugian karena gesekan (PS)
19. Daya Indikasi NmNeNi += (PS) (3-19)
Dimana :
Ni : daya indikasi (PS)
Ne : daya efektif (PS)
Nm : daya mekanis (PS)
20. Specific Fuel Consumption Effective
NeFCSFCe =
(3-20)
Dimana :
SFCe : Specific Fuel Consumption Effective
FC : konsumsi bahan bakar (kg/jam)
Ne : daya efektif (PS)
21. Specific Fuel Consumption Indicated
NiFCSFCi =
(3-21)
Dimana :
SFCi : Specific Fuel Consumption Indicated
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FC : konsumsi bahan bakar (kg/jam)
Ni : daya indikatif (PS)
22. Panas Hasil Pembakaran yang diubah menjadi Daya Efektif
NeQe .632= (3-22)
Dimana :
Qe : panas efektif (kcal/jam)
Ne : daya efektif (PS)
23. Panas yang hilang karena sebab lain
𝑄𝑝𝑝 = 𝑄𝑏 − 𝑄𝑒𝑔 − 𝑄𝑤 − 𝑄𝑒 (3-23)
Dimana :
Qpp : panas yang hilang karena sebab lain (kcal/jam)
Qb : panas hasil pembakaran (kcal/jam)
Qeg : panas yang terbawa gas buang (kcal/jam)
Qw : kerugian panas pendinginan (kcal/jam)
Qe : panas efektif (kcal/jam)
24. Efisiensi Thermal Indikasi
%100632××=QbNi
iη (3-24)
Dimana :
iη : efisiensi indikasi (%)
Ni : daya indikasi (PS)
Qb : panas hasil pembakaran (kcal/jam)
25. Efisiensi Mekanis
%100xNiNe
m =η (3-25)
Dimana :
mη : efisiensi mekanis (%)
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Ni : daya indikasif (PS)
Ne : daya efektif (PS)
26. Efisiensi Volumetrik
%100...60.. xiVdn
zGs
av γ
η = (3-26)
Dimana :
vη : efisiensi volumetric (%)
z : jumlah poros engkol
Vd : volume engkol (m3)
I : langkah mesin
Gs : massa alir udara melalui nozzle (kg/s)
n : putaran poros (rpm)
𝛾a : Berat jenis udara (kg/m3)
27. Perbandingan Udara dan Bahan Bakar
3600xFCGsR =
(3-27)
Dimana :
R : rasio udara bahan bakar
Gs : aliran udara melalui nozzle (kg/s)
FC : konsumsi bahan bakar (kg/jam)
28. Rasio Udara Bahan Bakar Teoritis
22222223,12 116,671,113,12)76,3(85,17 NOHCONOHC ++→++ (3-28)
HMCM
NMOMFARo s
βα
βα
βα
+
⎟⎠
⎞⎜⎝
⎛ ++⎟⎠
⎞⎜⎝
⎛ +=
22 476,3
4)/(
Dimana :
Ro : Rasio udara bahan bakar teoritis
2OM : Massa relatif oksigen
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2NM : Massa relatif nitrogen
CM : Massa relatif karbon
HM : Massa relatif hidrogen
29. Faktor Kelebihan Udara
RoR
=λ (3-29)
Dimana : λ : faktor kelebihan udara
R : rasio udara bahan bakar
Ro : rasio udara dalam bahan bakar teoritis
30. Faktor Koreksi Standard 5,0
⎥⎦
⎤⎢⎣
⎡=
st
st
TT
PP
A = 5,0
273273
⎥⎦
⎤⎢⎣
⎡
+
+
st
st
TT
PP
(3-30)
Dimana :
A : faktor koreksi
Pst : tekanan atmosfer = 760 mmHg
Tst : 25 ˚C
P : tekanan udara atsmosfer (mmHg)
T : temperatur ruangan (oC)
31. Daya Efektif Standard
( ) NeANe st .= (3-31)
Dimana :
( )stNe : daya efektif standar (PS)
A : faktor koreksi
Ne : daya efektif (PS)
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32. Torsi Efektif Standard
( ) TAT st .= (3-32)
Dimana :
( )stT : torsi efektif standar (kg.m)
A : faktor koreksi
T : torsi (kg.m)
33. Pemakaian Bahan Bakar Efektif Standard
( )A
SFCeSFCe st = (3-33)
Dimana :
SFCest : Pemakaian Bahan Bakar Efektif Standar
SFCe : Specific Fuel Consumption Effective
A : faktor koreksi
34. Analisa Gas Buang