Motor bakar adalah perangkat yang mengubah energi kimia menjadi energi mekanis. Di dunia ini, ada berbagai jenis motor bakar yang berbeda-beda, baik dalam prinsip kerjanya maupun dalam jenis bahan bakar yang digunakan. Salah satu jenis motor bakar yang menarik untuk dibahas adalah external combustion engine atau mesin pembakaran eksternal.
Mesin pembakaran eksternal adalah jenis motor bakar di mana pembakaran bahan bakar terjadi di luar mesin itu sendiri. Ini berarti bahwa panas yang dihasilkan dari proses pembakaran dikirimkan ke mesin melalui antarmuka termal, biasanya berupa fluida kerja seperti air atau gas. Salah satu contoh motor bakar yang termasuk dalam kategori ini adalah mesin uap.
Mesin uap adalah salah satu contoh paling terkenal dari external combustion engine. Prinsip kerjanya sangat sederhana: air dipanaskan dengan menggunakan bahan bakar seperti batu bara, kemudian uap panas yang dihasilkan digunakan untuk menggerakkan piston dalam mesin. Beberapa contoh penerapan mesin uap termasuk lokomotif, kapal uap, dan mesin tenaga termal yang digunakan dalam pembangkit listrik tenaga uap.
1. Steam Engine
Steam engines are a classic example of external combustion engines. These engines work by heating water in a boiler, which produces steam. The steam then enters a cylinder where it pushes a piston, converting the steam’s energy into mechanical work. Steam engines played a vital role during the industrial revolution, powering trains, ships, and factories. Their popularity declined with the invention of internal combustion engines, but they still hold a significant place in the history of transportation.
One advantage of steam engines is their ability to generate high torque at low speeds, making them suitable for tasks that require significant power output, such as hauling heavy loads or driving industrial machinery. Additionally, steam engines can be fueled by various energy sources, from coal and wood to petroleum and nuclear power, providing flexibility in their operations. Despite their efficiency limitations and size, steam engines remain an essential part of our technological heritage.
In conclusion, steam engines are a prime example of external combustion engines. They have powered various modes of transportation and played a crucial role in the industrial revolution. Though their popularity has waned over time, their historical significance cannot be overlooked.
2. Stirling Engine
The Stirling engine is another type of external combustion engine that operates on the principle of cyclical compression and expansion of gas. This engine uses a closed-loop system with two pistons, where one piston compresses the gas and the other expands it to generate work. The heat for the engine is supplied externally, making it an external combustion engine.
One notable advantage of the Stirling engine is its ability to run on any heat source, such as solar energy, geothermal energy, or even waste heat from industrial processes. This versatility allows Stirling engines to be used in various applications, including electricity generation, heating, and cooling systems. Additionally, Stirling engines offer excellent thermal efficiency and produce low noise and vibration levels.
In conclusion, the Stirling engine is a remarkable external combustion engine that offers versatility and high thermal efficiency. Its ability to run on various heat sources makes it a promising alternative for sustainable power generation and other applications.
3. Hot Air Engine
The hot air engine, also known as the caloric engine, is an external combustion engine that operates by using the expansion of air when heated. These engines consist of a cylinder and piston, where air is heated in a separate chamber and then transferred to the cylinder for expansion. The expansion of the heated air forces the piston to move, creating mechanical work.
One notable advantage of hot air engines is their ability to run on any heat source, similar to Stirling engines. They can utilize solar collectors, waste heat, or even burning solid fuels. Hot air engines have been historically used in applications such as water pumping, grinding grain, and generating electricity in small power plants. However, their efficiency limitations and lower power output compared to internal combustion engines have restricted their widespread use.
In conclusion, hot air engines represent another example of external combustion engines that utilize the expansion of heated air to generate mechanical work. Although their use has been limited, they have found niche applications in the past.
4. Pulsejet Engine
The pulsejet engine is a unique type of external combustion engine that operates by creating a series of rapid combustions or pulses. These engines consist of a combustion chamber with an inlet and an outlet. The combustion of fuel-air mixture inside the chamber creates a high-pressure pulse that is expelled through the outlet, producing thrust.
Pulsejet engines were mainly used during World War II as propulsion systems for the infamous V-1 flying bomb. Their simple design and low-cost production made them suitable for this purpose. However, their limited efficiency, high fuel consumption, and noisy operation have largely restricted their use in modern applications, except for certain specialized fields such as model aircraft or unmanned aerial vehicles (UAVs).
In conclusion, pulsejet engines are a unique type of external combustion engine known for their distinctive pulsating operation. Although their applications are limited, they have played historical roles and continue to be used in specific fields.
5. Oxy-fuel Combustion Engine
The oxy-fuel combustion engine, as the name suggests, relies on external combustion to generate power. In this engine, a fuel, such as natural gas or hydrogen, is burned in a combustion chamber with pure oxygen instead of air. The combustion products, including steam, are expanded in a cylinder to generate power.
This type of engine offers several advantages, including lower greenhouse gas emissions and improved fuel efficiency compared to traditional internal combustion engines. The use of pure oxygen in the combustion process allows for more complete fuel burn, resulting in reduced pollution. Oxy-fuel combustion engines have been primarily explored for power generation, especially in integrated gasification combined cycle (IGCC) systems, where the engine’s waste heat can be captured for additional power production or other uses.
In conclusion, oxy-fuel combustion engines represent an external combustion alternative that offers improved fuel efficiency and reduced emissions. While their applications are currently limited, they hold promise for future power generation systems.
6. Organic Rankine Cycle (ORC) Engine
The Organic Rankine Cycle (ORC) engine is a type of external combustion engine that operates based on the Rankine cycle, where a working fluid with a lower boiling point than water is employed. In this engine, heat is supplied externally to vaporize the working fluid. The resulting high-pressure vapor is then expanded in a turbine, driving a generator to produce electricity.
One of the significant advantages of ORC engines is their ability to utilize low-temperature heat sources. This makes them ideal for diverse applications, such as waste heat recovery in industrial processes, geothermal power generation, and biomass energy utilization. ORC engines are known for their high efficiency in converting heat into electricity, making them an environmentally friendly alternative in various power generation scenarios.
In conclusion, the ORC engine is an external combustion engine designed for electricity generation using low-temperature heat sources. Its high efficiency and versatility have made it a popular choice in renewable energy systems and waste heat recovery applications.
7. Nitrogen Engine
The nitrogen engine is an unconventional external combustion engine concept that utilizes the expansion of liquid nitrogen to generate power. In this engine, liquid nitrogen is stored in a tank, and upon demand, it is rapidly vaporized by heat transfer from the surrounding environment. The expanding nitrogen gas is then used to drive a piston or a turbine, generating mechanical work.
This engine concept offers several advantages, such as zero greenhouse gas emissions and potential energy storage capabilities. As liquid nitrogen has the ability to store large amounts of energy, the nitrogen engine could be used as a form of energy storage in renewable energy systems or as a power source in zero-emission vehicles. However, challenges remain in terms of the low energy density of liquid nitrogen and the development of efficient heat transfer systems.
In conclusion, the nitrogen engine represents an innovative approach to external combustion engines, offering the potential for zero-emission power generation and energy storage. Further research and development are needed to overcome existing challenges and realize its full potential.