Rabu, 14 Januari 2009

Engine cycle

Engine cycle
Idealised P/V diagram for two stroke Otto cycle

Two-stroke

Main article: Two-stroke cycle

This cycle has one power stroke for every two strokes of the piston (up-down) and exhaust of the exhaust gases and charging of the cylinder happens at much the same time.

The steps involved here are:

1. Intake and exhaust stroke: Exhaust is released and air and vaporized fuel are drawn in.
2. Compression stroke: Fuel vapor and air are compressed and ignited.
3. power stroke: piston is pushed downwards by the hot exhaust gases.

Four-stroke

Main article: Four-stroke cycle

Idealised Pressure/volume diagram of the Otto cycle showing combustion heat input Qp and waste exhaust output Qo, the power stroke is the top curved line, the bottom is the compression stroke

Engines based on the four-stroke ("Otto cycle") have one power stroke for every four strokes (up-down-up-down) and employ spark plug ignition. Combustion occurs rapidly, and during combustion the volume varies little ("constant volume").[6] They are used in cars, larger boats, some motorcycles, and many light aircraft. They are generally quieter, more efficient, and larger than their two-stroke counterparts.

The steps involved here are:

1. Intake stroke: Air and vaporized fuel are drawn in.
2. Compression stroke: Fuel vapor and air are compressed and ignited.
3. Combustion stroke: Fuel combusts and piston is pushed downwards.
4. Exhaust stroke: Exhaust is driven out. During the 1st, 2nd, and 4th stroke the piston is relying on power and the momentum generated by the other pistons. In that case, a four cylinder engine would be less powerful than a six or eight cylinder engine.

There are a number of variations of these cycles, most notably the Atkinson and Miller cycles. The diesel cycle is somewhat different.

Diesel cycle

Main article: diesel cycle

P-v Diagram for the Ideal Diesel cycle. The cycle follows the numbers 1-4 in clockwise direction.

Most truck and automotive diesel engines use a cycle reminiscent of a four-stroke cycle, but with a compression heating ignition system, rather than needing a separate ignition system. This variation is called the diesel cycle. In the diesel cycle, diesel fuel is injected directly into the cylinder so that combustion occurs at constant pressure, as the piston moves, rather than with the four stroke with the piston essentially stationary.

Five-stroke

Engines based on the five-stroke cycle are a variant of the four-stroke cycle. Normally, the four cycles are intake, compression, combustion, and exhaust. The fifth cycle, which was added by Delautour,[7] is refrigeration. Engines running on a five-stroke cycle are claimed to be up to 30% more efficient than equivalent four-stroke engines.

Six-stroke

The six stroke engine captures the wasted heat from the four-stroke Otto cycle and creates steam, which simultaneously cools the engine while providing a free power stroke. This removes the need for a cooling system making the engine lighter while giving 40% increased efficiency over the Otto Cycle.

Basic process

Basic process

Internal combustion engines have 4 basic steps:

  1. Intake
    • Combustible mixtures are emplaced in the combustion chamber
  2. Compression
    • The mixtures are placed under pressure
  3. Combustion/Expansion
    • The mixture is burnt, almost invariably a deflagration, although a few systems involve detonation. The hot mixture is expanded, pressing on and moving parts of the engine and performing useful work.
  4. Exhaust
    • The cooled combustion products are exhausted

Many engines overlap these steps in time, jet engines do all steps simultaneously at different parts of the engines.

Combustion

All internal combustion engines depend on the exothermic chemical process of combustion: the reaction of a fuel, typically with oxygen from the air—although other oxidizers such as nitrous oxide may be employed. The combustion process typically results in the production of a great quantity of heat, as well as the production of steam and carbon dioxide and other chemicals at very high temperature; the temperature reached is determined by the chemical make up of the fuel and oxidisers (see stoichiometry).

The most common modern fuels are made up of hydrocarbons and are derived mostly from fossil fuels (petroleum). Fossil fuels include dieselfuel, gasoline and petroleum gas, and the rarer use of propane. Except for the fuel delivery components, most internal combustion engines that are designed for gasoline use can run on natural gas or liquefied petroleum gases without major modifications. Large diesels can run with air mixed with gases and a pilot diesel fuel ignition injection. Liquid and gaseous biofuels, such as ethanol and biodiesel (a form of diesel fuel that is produced from crops that yield triglycerides such as soybean oil), can also be used. Some engines with appropriate modifications can also run on hydrogen gas.

All internal combustion engines must achieve ignition in their cylinders to create combustion. Typically engines use either a spark ignition (SI) method or a compression ignition (CI) system. In the past, other methods using hot tubes or flames have been used.

Gasoline Ignition Process

Gasoline engine ignition systems generally rely on a combination of a lead-acid battery and an induction coil to provide a high-voltage electrical spark to ignite the air-fuel mix in the engine's cylinders. This battery is recharged during operation using an electricity-generating device such as an alternator or generator driven by the engine. Gasoline engines take in a mixture of air and gasoline and compress it to not more than 12.8 bar, then use a spark plug to ignite the mixture when it is compressed by the piston head in each cylinder.

Diesel Ignition Process

Diesel engines and HCCI(Homogeneous charge compression ignition) engines, rely solely on heat and pressure created by the engine in its compression process for ignition. The compression level that occurs is usually twice or more than a gasoline engine. Diesel engines will take in air only, and shortly before peak compression, a small quantity of diesel fuel is sprayed into the cylinder via a fuel injector that allows the fuel to instantly ignite. HCCI type engines will take in both air and fuel but continue to rely on an unaided auto-combustion process, due to higher pressures and heat. This is also why diesel and HCCI engines are more susceptible to cold-starting issues, although they will run just as well in cold weather once started. Light duty diesel engines with indirect injection in automobiles and light trucks employ glowplugs that pre-heat the combustion chamber just before starting to reduce no-start conditions in cold weather. Most diesels also have a battery and charging system; nevertheless, this system is secondary and is added by manufacturers as a luxury for the ease of starting, turning fuel on and off (which can also be done via a switch or mechanical apparatus), and for running auxiliary electrical components and accessories. Most new engines rely on electrical and electronic control system that also control the combustion process to increase efficiency and reduce emissions.

Basic process

Basic process

Internal combustion engines have 4 basic steps:

  1. Intake
    • Combustible mixtures are emplaced in the combustion chamber
  2. Compression
    • The mixtures are placed under pressure
  3. Combustion/Expansion
    • The mixture is burnt, almost invariably a deflagration, although a few systems involve detonation. The hot mixture is expanded, pressing on and moving parts of the engine and performing useful work.
  4. Exhaust
    • The cooled combustion products are exhausted

Many engines overlap these steps in time, jet engines do all steps simultaneously at different parts of the engines.

Combustion

All internal combustion engines depend on the exothermic chemical process of combustion: the reaction of a fuel, typically with oxygen from the air—although other oxidizers such as nitrous oxide may be employed. The combustion process typically results in the production of a great quantity of heat, as well as the production of steam and carbon dioxide and other chemicals at very high temperature; the temperature reached is determined by the chemical make up of the fuel and oxidisers (see stoichiometry).

The most common modern fuels are made up of hydrocarbons and are derived mostly from fossil fuels (petroleum). Fossil fuels include dieselfuel, gasoline and petroleum gas, and the rarer use of propane. Except for the fuel delivery components, most internal combustion engines that are designed for gasoline use can run on natural gas or liquefied petroleum gases without major modifications. Large diesels can run with air mixed with gases and a pilot diesel fuel ignition injection. Liquid and gaseous biofuels, such as ethanol and biodiesel (a form of diesel fuel that is produced from crops that yield triglycerides such as soybean oil), can also be used. Some engines with appropriate modifications can also run on hydrogen gas.

All internal combustion engines must achieve ignition in their cylinders to create combustion. Typically engines use either a spark ignition (SI) method or a compression ignition (CI) system. In the past, other methods using hot tubes or flames have been used.

Gasoline Ignition Process

Gasoline engine ignition systems generally rely on a combination of a lead-acid battery and an induction coil to provide a high-voltage electrical spark to ignite the air-fuel mix in the engine's cylinders. This battery is recharged during operation using an electricity-generating device such as an alternator or generator driven by the engine. Gasoline engines take in a mixture of air and gasoline and compress it to not more than 12.8 bar, then use a spark plug to ignite the mixture when it is compressed by the piston head in each cylinder.

Diesel Ignition Process

Diesel engines and HCCI(Homogeneous charge compression ignition) engines, rely solely on heat and pressure created by the engine in its compression process for ignition. The compression level that occurs is usually twice or more than a gasoline engine. Diesel engines will take in air only, and shortly before peak compression, a small quantity of diesel fuel is sprayed into the cylinder via a fuel injector that allows the fuel to instantly ignite. HCCI type engines will take in both air and fuel but continue to rely on an unaided auto-combustion process, due to higher pressures and heat. This is also why diesel and HCCI engines are more susceptible to cold-starting issues, although they will run just as well in cold weather once started. Light duty diesel engines with indirect injection in automobiles and light trucks employ glowplugs that pre-heat the combustion chamber just before starting to reduce no-start conditions in cold weather. Most diesels also have a battery and charging system; nevertheless, this system is secondary and is added by manufacturers as a luxury for the ease of starting, turning fuel on and off (which can also be done via a switch or mechanical apparatus), and for running auxiliary electrical components and accessories. Most new engines rely on electrical and electronic control system that also control the combustion process to increase efficiency and reduce emissions.

Basic process

Basic process

Internal combustion engines have 4 basic steps:

  1. Intake
    • Combustible mixtures are emplaced in the combustion chamber
  2. Compression
    • The mixtures are placed under pressure
  3. Combustion/Expansion
    • The mixture is burnt, almost invariably a deflagration, although a few systems involve detonation. The hot mixture is expanded, pressing on and moving parts of the engine and performing useful work.
  4. Exhaust
    • The cooled combustion products are exhausted

Many engines overlap these steps in time, jet engines do all steps simultaneously at different parts of the engines.

Combustion

All internal combustion engines depend on the exothermic chemical process of combustion: the reaction of a fuel, typically with oxygen from the air—although other oxidizers such as nitrous oxide may be employed. The combustion process typically results in the production of a great quantity of heat, as well as the production of steam and carbon dioxide and other chemicals at very high temperature; the temperature reached is determined by the chemical make up of the fuel and oxidisers (see stoichiometry).

The most common modern fuels are made up of hydrocarbons and are derived mostly from fossil fuels (petroleum). Fossil fuels include dieselfuel, gasoline and petroleum gas, and the rarer use of propane. Except for the fuel delivery components, most internal combustion engines that are designed for gasoline use can run on natural gas or liquefied petroleum gases without major modifications. Large diesels can run with air mixed with gases and a pilot diesel fuel ignition injection. Liquid and gaseous biofuels, such as ethanol and biodiesel (a form of diesel fuel that is produced from crops that yield triglycerides such as soybean oil), can also be used. Some engines with appropriate modifications can also run on hydrogen gas.

All internal combustion engines must achieve ignition in their cylinders to create combustion. Typically engines use either a spark ignition (SI) method or a compression ignition (CI) system. In the past, other methods using hot tubes or flames have been used.

Gasoline Ignition Process

Gasoline engine ignition systems generally rely on a combination of a lead-acid battery and an induction coil to provide a high-voltage electrical spark to ignite the air-fuel mix in the engine's cylinders. This battery is recharged during operation using an electricity-generating device such as an alternator or generator driven by the engine. Gasoline engines take in a mixture of air and gasoline and compress it to not more than 12.8 bar, then use a spark plug to ignite the mixture when it is compressed by the piston head in each cylinder.

Diesel Ignition Process

Diesel engines and HCCI(Homogeneous charge compression ignition) engines, rely solely on heat and pressure created by the engine in its compression process for ignition. The compression level that occurs is usually twice or more than a gasoline engine. Diesel engines will take in air only, and shortly before peak compression, a small quantity of diesel fuel is sprayed into the cylinder via a fuel injector that allows the fuel to instantly ignite. HCCI type engines will take in both air and fuel but continue to rely on an unaided auto-combustion process, due to higher pressures and heat. This is also why diesel and HCCI engines are more susceptible to cold-starting issues, although they will run just as well in cold weather once started. Light duty diesel engines with indirect injection in automobiles and light trucks employ glowplugs that pre-heat the combustion chamber just before starting to reduce no-start conditions in cold weather. Most diesels also have a battery and charging system; nevertheless, this system is secondary and is added by manufacturers as a luxury for the ease of starting, turning fuel on and off (which can also be done via a switch or mechanical apparatus), and for running auxiliary electrical components and accessories. Most new engines rely on electrical and electronic control system that also control the combustion process to increase efficiency and reduce emissions.

PENGEMBANGAN PEMBANGKIT THERMOELEKTRIK

PENGEMBANGAN PEMBANGKIT THERMOELEKTRIK DENGAN MEMANFAATKAN PANAS GAS BUANG MOTOR BAKAR UNTUK KENDARAAN HYBRID

Penelitian ini berkaitan tentang pemanfaatan energy panas yang terbuang pada kendaraan bermotor yang akan dijadikan energy listrik. Konsep yang digunakan adalah konsep Seebeck. Apabila terdapat dua sumber temperatur yang berbeda pada dua material semi konduktor makah akan mengalir arus listrik pada material tersebut. Konsep ini lebih dikenal dengan pembangkit termoelektrik. Pada penelitian ini, konsep termoelektrik akan diaplikasikan pada mobil hibrida. Kemudian sumber temperatur tinggi pada penelitian ini adalah gas buang kendaraan bermotor yang berkisar antara 200-300oC sementara sumber temperature rendahnya adalah lingkungan yang berkisar 30-35oC. Energi yang dibangkitkan kemudaian akan disimpan di dalam baterai atau langsung digunakan untuk menggerakan motor listrik pada kendaraan hybrid. Pada penelitian terdapat 4 tahapan yakni karakteristik distribusi temperatur gas buang, karakteristik termoelektrik, rancangan bangun pembangkit termoelektrik dan uji unjuk kerja prototype yang dihasilkan. Hasil penelitian ini diharapkan dapat mengurangi konsumi bahan bakar minyak untuk kendaran bermotor dan juga mengurangi emisi gas buang ke lingkungan.

Selasa, 13 Januari 2009

Apa yang Terjadi didalam Silinder...

TEORI MOTOR DIESEL
SIKLUS DAN PROSES PEMBAKARAN MOTOR DIESEL

• Mengidentifikasi siklus kerja motor Diesel
• Mengidentifikasi perbedaan siklus 4 & 2 tak.

Apa Yang Terjadi di dalam Silinder?Seperti telah dikemukakan sebelumnya bahwa motor Diesel merupa-kan salah satu jenis dari mesin pembangkit tenaga. Motor Diesel termasuk mesin pembakaran dalam atau internal combustion engine, artinya proses pembentukan energy panas terjadi di dalam mesin itu sendiri. Sekarang apa yang terjadi di dalam mesin? Mesin berusaha merubah energy kimia menjadi energy mekanik yang dimafaatkan sebagai sumber tenaga.Energy kimia bahan bakar yang dikenal sebagai hidrocarbon (CH), disenyawakan dengan oksigen agar dapat dilakukan proses pembentukan energy panas melalui proses pembakaran. Pertama-tama mesin berusaha merubah bentuk fisik bahan bakar dari bentuk cair menjadi bentuk gas. Bahan bakar dikabutkan, agar mudah menguap atau menjadi bentuk gas. Kondisi ini baru memungkinkan bahan bakar bersenyawa dengan oksigen dari udara. Konsentrasi ini akan memungkinkan terjadinya proses pembakaran, setelah ketiga syarat pembakaran yaitu bakan bakar, oksigen dan panas saling berhubungan.Kalor hasil pembakaran tersebut selanjutnya menyebabkan terjadi-nya pemuaian gas di dalam silinder, yang diindikasikan naiknya tekanan. Tekanan tersebut selanjutnya dimanfaatkan untuk menghasilkan energy mekanik berupa putaran pada poros engkol. Dengan demikian mesin akhirnya menghasilkan tenaga seperti yang diharapkan.Siklus Motor DieselMotor Diesel untuk menghasilkan tenaga/daya seperti yang diharap-kan melalui serangkaian proses yang terus berulang-ulang, atau dikenal dengan terjadinya siklus yang berulang-ulang. Siklus pada motor Diesel terdiri dari empat proses, yaitu proses isap, kompresi, usaha dan proses buang. Terdapat dua cara dalam menyelesaikan setiap siklus tersebut, cara pertama diselesaikan dengan empat langkah piston, atau dua putaran poros engkol. Cara pertama disebut dengan motor Diesel empat Tak. Cara kedua siklus diselesaikan dalam dua langkah piston atau satu putaran poros engkol, cara ini disebut dengan motor Diesel dua Tak.
Berikut ini rangkaian penyelesaian siklus pada motor Diesel 4 Tak.
Gambar 1. Siklus Motor Diesel 4 Tak
Proses pertama, adalah proses isap. Piston bergerak dari TMA menuju ke TMB, dan proses isap dimulai saat katup isap/masuk mulai ter-buka. Kevacuuman di dalam silinder menyebabkan terjadinya proses isap. Pada motor Diesel yang masuk kedalam silinder hanya udara.Proses kedua, adalah proses kompresi. Proses ini dimulai saat katup mulai tertutup dan piston bergerak dari TMB ke TMA. Piston mengkompresikan udara, hingga temperatur dan tekanan udara naik. Temperatur udara naik hingga mencapai titik nyala bahan bakar (solar). Proses kompresi salah tugasnya, adalah menyediakan salah satu syarat untuk terjadinya proses pembakkaran, yaitu panas untuk menyalakan.Proses ketiga, adalah proses usaha. Pada akhir langkah kompresi bahan bakar diinjeksikan atau dikabutkan ke dalam silinder. Dengan demikian kini di dalam silinder terdapat tiga unsur proses pembakaran, yaitu oksigen (dari udara), CH (dari bahan bakar), dan panas (yang mencapai titik nyala bahan bakar). Berkumpulnya ketiga unsur tersebut menyebabkan terjadinya proses pembakaran di dalam silinder, dan terjadi kenaikan temperatur dan tekanan. Tekanan hasil pemabakaran dikalikan dengan luas piston akan terjadi gaya (force) yang mendorong piston melakukan proses usaha dari TMA menuju TMB.Proses keempat, adalah proses buang. Seperti yang telah dijelas-kan sebelumnya, agar motor Diesel dapat mengahsilkan tenaga/daya secara terus-menerus, maka akan terjadi proses pengulangan siklus yang terus menerus juga. Untuk bisa mengulang siklus berikutnya, maka segala sesuatu yang ada di dalam silinder yang merupakan sisa dari siklus sebelumnya harus dikeluarkan dari dalam silinder, atau dibuang. Oleh karena itu, piston bergerak dari TMB ke TMA untuk mengeluarkan hasil pembakaran yang telah di pergunakan untuk menghasilkan daya. Materi ini sering disebut dengan gas buang, yang masih mengandung panas/kalor dan tekanan yang cukup tinggi. Untuk itu agar tidak menjadi materi pencemar udara, gas buang dikelola menggunakan exhaust system. Sehingga exhaust system bertugas untuk memproses gas buang layak untuk dibuang keudara luar. Proses pembuangan ini dimulai saat katup buang muali terbuka dan akan berakhir saat katup buang mulai tertutup.Berikut adalah siklus yang terjadi pada motor Diesel 2 Tak. Siklus motor tetap terdiri dari empat proses yaitu isap, kompresi, usaha, dan buang. Keempat proses tersebut pada motor Diesel 2 Tak diselesaikan dalam dua langkah piston atau satu putaran poros engkol. Untuk mendukung kerja motor Diesel 2 Tak dilengkapi dengan pompa bilas, yang dalam gambar berikut ini digunakan sebuah blower. Pompa bilas atau blower dipergunakan untuk memasukan udara kedalam silinder.
Gambar 2. Siklus Motor Diesel 2 Tak.Proses isap dan buang berlangsung pada waktu bersamaan, yaitu saat katup membuka saluran buang dan diikuti oleh terbukanya saluran masuk yang dibuka oleh piston yang bergerak ke TMB. Dengan terbukanya katup buang terlebih dahulu, maka gas buang telah mempunyai aliran kearah ke saluran buang. Kondisi ini diikuti oleh udara baru yang masuk kedalam silinder baik karena terbawa aliran gas buang dan karena tekanan dari pompa bilas. Proses pemasukan ini akan berlangsung terus, hingga saluran masuk tertutup oleh piston. Sementara proses pembuangan akan berakhir saat katup buang tertutup. Sehingga proses isap dimulai saat saluran masuk mulai terbuka oleh piston dan berakhir saat ditutup oleh piston. Sedangkan proses pembuangan diawali saat katup buang terbuka, dan diakhiri saat katup buang tertutup. Saat saluran masuk terbuka hingga katup buang tertutup disebut dengan proses pembilasan, yaitu penggantian isi ruang silinder dari gas buang oleh gaas baru. Lihat prosesnya seperti pada gambar 2 sebelah kiri.Proses Kompresi, dimulai saat saluran masuk & buang tertutup, dan piston bergerak dari TMB ke TMA. Piston memampatkan udara di dalam silinder, hingga naik tekanan dan temperaturnya. Pada akhir langkah kompresi temperatur udara mencapai titik nyala bahan bakar, sebagai salah satu perrsyaratan terjadinya proses pembakaran. Proses kompresi akan berlangsung hingga piston mencapai TMA. Lihat gambar 2 yang tengah.Proses usaha, diawali dari TMA hingga katup buang terbuka. Sebelum TMA bahan bakar diinjeksi/dikabutkan kedalam silinder. Dengan demikian di dalam silinder berkumpul tiga unsur terjadinya proses pembakaran, yaitu udara, bahan bakar, dan panas. Oleh karena itu terjadilah proses pembakaran di dalam silinder, yang menghasilkan panas untuk menaikan tekanan di dalam silinder. Tekanan hasil pembakaran inilah yang dikonversikan menjadi gaya yang mendorong piston melakukan langkah usaha. Langkah usaha akan berakhir saat katup buang mulai dibuka, dan di ikuti dengan proses pembuangan dan pemasukan seperti dijelaskan di atas. Lihat gambar 2 yang kanan.