Laporan Praktek Motor Diesel Minggu Ke 12

7/26/2019 Laporan Praktek Motor Diesel Minggu Ke 12

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1. Tujuan Praktek

a. Mahasiswa dapat menjelaskan apa itu bagian/komponen motor diesel 4 tak single cylinder.b. Mahasiswa dapat melakukan running test single cylinder diesel engine procedure.

c. Mahasiswa dapat menginspeksi inspeksi motor diesel 4 tak single cylinder.

2. Alat dan Bahan

a. .. d. .......

b. .. e. ........c. .. f.

3. Tinjauan Teori

Motor diesel sebagai sebuah sumber tenaga penggerak memiliki prinsip yang hampirsama dengan motor bensin (gasoline engine) dimana energi dihasilkan oleh pembakaran

bahan bakar, Ada beberapa perbedaan utama antara karakteristik mesin bensin dan mesindiesel. Mesin diesel menggunakan prinsip auto - ignition (terbakar sendiri). Sedangkan mesin

bensin menggunakan prinsip spark - ignition (pembakaran yang dipicu oleh percikan api padabusi). Oleh karenanya motor diesel sering juga disebut dengan compression ignitionengine.

Agar dapat mencapai suhu dan tekanan pembakaran, tekanan kompresi pada mesin dieseldiusahakan mampu mencapai 30 45 kg/cm2, agar temperatur udara yang dikompresikan

mencapai 500 derajat celsius, sehingga bahan bakar mampu terbakar dengan sendirinya tanpadipicu oleh letikan bunga api dari busi.

Untuk dapat mencapai tekanan dan temperatur yang demikian, pada motor diesel harusmemiliki perbandingkan kompresi yang lebih tinggi kira-kira mencapai 25:1 dan

membutuhkan gaya yang lebih besar untuk memutarnya. Sehingga motor diesel memerlukanalat pemutar seperti motor starter dan baterai yang berkapasitas besar pula. Disamping itu

motor diesel memiliki efisiensi panas yang sangat tinggi, hemat konsumsi bahan bakar,

memiliki kecepatan lebih rendah dibanding mesin bensin, getarannya sangat besar dan agakberisik, momen yang didapatkan lebih besar, sehingga motor ini umumnya digunakan padakendaraan niaga, kendaraan penumpang dan sebagai motor penggerak lainnya.

Karena tekanan pembakaran yang tinggi, maka mesin diesel harus dibuat dari bahan yangtahan terhadap tekanan tinggi dan harus mempunyai struktur yang sangat kuat. Disamping itu

getaran motor yang dihasilkan sangat besar, ini diakibatkan oleh tekanan pembakaranmaksimum yang dicapai hampir dua kali lipat lebih besar dari pada motor bensin, sehingga

suara dan getaran mesin diesel menjadi lebih besar.

3.1 Prinsip Siklus Kerja Motor Diesel 4 Langkah

Gambar 1. Prinsip Kerja Motor Diesel

Praktek : Motor DieselSemester : V

Nama :

NIM :

NilaiJudul : Labelling engineTanggal :

Waktu : 2 x 45 menit

Lab : Otomotif


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1. Langkah pertama adalah langkah hisap. Pada langkah ini, piston akan bergerak dari titikmati atas (TMA) ke titik mati bawah (TMB). Selanjutnya, katup hisap akan terbuka

sebelum mencapai TMA dan katup buang akan tertutup. Akibatnya, akan terjadikevakuman di dalam silinder yang menyebabkan udara murni masuk ke dalam silinder.

2. Sedangkan pada langkah kedua (langkah kompresi), piston bergerak sebaliknya, yaitu

dari TMB ke TMA. Katup hisap tertutup sementara katup buang akan terbuka. Udarakemudian akan dikompresikan sampai pada tekanan dan suhunya menjadi 30kg/cm2dan

suhu 500 celsius.

3. Pada langkah ketiga (langkah usaha), katup hisap tertutup, katup buang juga tertutup daninjektor menyemprotkan bahan bakar. Sehingga, terjadi pembakaran yang menyebabkan

piston bergerak dari TMA ke TMB.4. Dan pada langkah keempat (langkah buang), hampir sama dengan langkah hisap, yaitu

piston bergerak dari TMB ke TMA. Namun, katup hisap akan tertutup dan katup buangakan terbuka. Sedangkan piston akan bergerak mendorong gas sisa pembakaran keluar.

Gambar 2. Siklus udara standar motor diesel

Sistim bahan bakar (fuel system) pada motor diesel memiliki peranan yang sangatpenting dalam menyediakan dan mensupply sejumlah bahan bakar yang dibutuhkan sesuai

dengan kapasitas mesin, putaran motor dan pembebanan motor. Oleh karenannyaperformance fuel sistem sangat menentukan kinerja dari motor diesel. Seperti pada gambar

dibawah ini, sistim bahan bakar pada motor diesel terdiri dari beberapa komponen utamadiantaranya tanki bahan bakar, feed pump atau pompa penyalur, filter bahan bakar, pompa

injeksi dan nozzle.

Gambar 3. Sistem bahan bahan bakar motor diesel


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Pada mesin diesel terdapat berbedaan yang mendasar jika dibandingkan dengan mesinbensin, volume penyemprotan bahan bakar pada mesin diesel diatur sedemikian rupa dan

tidak tergantung dari pembukaan katup gas, hanya saja governor akan bekerja sesuai dengangerakan katup gas. Pada waktu pedal gas ditekan secara konstan maka putaran mesin akan

turun bila beban mesin bertambah, misalnya pada saat tanjakan, untuk mengatasi hal ini

maka governor akan menambah volume penyemprotan bahan bakar agar mesin tidak matidan putaran mesin dapat dipertahankan. Untuk mengontrol jumlah (volume) bahanbakaryang diinjeksikan pada pompa injeksi dilengkapi dengan unit governor. Governor

dirancang untuk mengatur secara otomatis putaran dan daya mesin dengan mengontrolvolume penyemprotan berdasarkan beban mesin dan penekanan pedal gas. Governor bekerja

dengan menggerakkan rak pengontrol pompa injeksi dan rak pengontrol akan mengaturlangkah efektif plunyer.

3.2 Praktek Motor Diesel 4 Tak Single Cylinder


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3.3 Mekanisme Katup Motor Diesel 4 Tak Single Cylinder

Mekanisme katup pada motor diesel generator 4 tak berfungsi untuk mengaturpemasukan udara murni dan pengeluaran gas sisa pembakaran dengan cara membuka dan

menutup kedua katup. Mekanisme katup pada motor diesel 4 tak terdiri dari : poros bubungan(camshaft), pengungkit (tappet), batang pendorong (pushrod), tuas penekan katup (rocker arm)

dan katup beserta pegas pengembalinya.Cara kerja mekanisme katup yaitu : saat motor bekerja roda gigi poros engkol berputar

menggerakkan roda gigi bubungan sehingga poros bubungan juga ikut berputar. Karenapermukaan poros bubungan berbentuk eksentris (lonjong) maka pengungkit (tappet) yang

berhubungan dengannya cenderung bergerak naik turun sesuai dengan bentuk permukaan porosbubungan yang menggerakkannya. Gerak naik turun tappet tersebut diteruskan oleh batang

pendorong (push-rod) ke tuas penekan katup (rocker-arm) sehingga menekan (katup terbuka) danmembebaskan katup (katup tertutup) secara bergantian mengikuti putaran poros bubungan yang

lonjong (eksentrik). Urutan kerja mekanisme katup di atas bila dibuat ke dalam diagram alir(flow chart) adalah sebagai berikut :

3.4 Sistem Bahan Bakar Motor Diesel 4 Tak Single CylinderSecara sederhana sistem bahan bakar pada motor diesel berfungsi untuk menyalurkan

bahan bakar ke ruang bakar dengan takaran yang sesuai dengan kerja motor diesel tersebut.


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Komponen utama dari sistem bahan bakar motor diesel 4 tak selinder tunggal (horizontal)meliputi : (a). tangki bahan bakar, (b) keran, (c) saringan bahan bakar, (d) pompa injeksi

bahan bakar, (e) pipa penyalur dan pipa tekanan tinggi serta (f) injector (katup injeksi bahanbakar).

Prinsip kerja motor diesel 4 tak single cylinder sebagai berikut :Ketika keran bahan bakar diputar ke posisi membuka maka bahan bakar akan mengalir ke

pompa injeksi dengan melalui saringan bahan bakar terlebih dahulu. Saat mesin mulaiberputar, pompa injeksi juga turut bekerja atau memompakan bahan bakar ke injector (a)

melalui pipa tekanan tinggi. Tekanan bahan bahan bakar yang tinggi mengakibatkan pegas

penahan katup nozzle di dalam injector terdesak (membuka nozzle) dan bahan bakarterinjeksikan ke dalam ruang bakar (b). Setelah proses injeksi bahan bakar selesai, maka katupnozzle akan menutup kembali (c) karena adanya tekanan pegas pengembali.

Bahan bakar (solar) yang berlebihan pada injector kemudian dialirkan kembali ke tangkibahan bakar berkat adanya relief valve dan saluran pengembali. Dengan demikian tidak

terjadi pemborosan bahan bakar, karena bahan bakar yang tersisa/berlebih saat peristiwapenyemprotan bahan bakar dikembalikan lagi ke tangki bahan bakar. Aliran bahan bakar

(solar) pada setiap komponen sistem bahan bakar tersebut di atas bila dibuat ke dalamdiagram alir (flow chart) adalah sebagai berikut :


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TUGAS PRAKTEK TERSTRUKTUR I1.1 Buatlah gambar sederhana (sket) langkah kerja dan diagram kerja katup pada motor

diesel 4 tak single cylinder.1.2 Berikan penjelasan ringkas tentang gambar sederhana (sket) tersebut dengan

menggunakan kata - kata sendiri sesuai pemahaman anda.

1.3

Uraikan komponen konstruksi utama sebuah motor diesel 4 tak single cylinder.1.4 Jelaskan langkah kerja motor diesel 4 tak single cylinder secara lengkap dengan bantuangambar ( gambar sketsa ).

1.5 Jelaskan cara kerja mekanisme katup pada motor diesel 4 tak single cylinder denganmenganalisa gambar secara lengkap.

TUGAS PRAKTEK TERSTRUKTUR II

2.1 Sebutkan fungsi sistem bahan bakar pada motor diesel 4 tak single cylinder.2.2 Sebutkan fungsi masing-masing komponen sistem bahan bakar pada motor diesel 4 tak

single cylinder secara lengkap.2.3 Jelaskan cara kerja sistem bahan bakar pada motor diesel 4 tak single cylinder secara

sistematis.JAWABAN........................................................................................................................................................................................................................................................................................

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Dosen Teknisi Keterangan

Diperiksa,

Jember, Desember 2014

Ahmad Robiul Awal.U ST., MT

Laporan Praktek Motor Diesel Minggu Ke 12

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