Dry Cooler System For Cooling Combustion Engine Using Biofuels
Dry Cooler System For Cooling Combustion Engine Using Biofuels
Biofuels (e.g. FAME biodiesel, E85 ethanol gasoline, HVO hydrogenated vegetable oil, etc.) have different physicochemical properties (e.g. calorific value, oxygen content, combustion rate) from conventional diesel/gasoline, which leads to differences in combustion processes and heat production characteristics of internal combustion engines, and thus affects the design requirements of the cooling system:
Combustion Temperature and Heat Load
Biofuels have a higher oxygen content (e.g. about 10% for biodiesel) and burn more fully, but some types (e.g. pure ethanol) have a lower calorific value (about 26.8 MJ/kg, lower than gasoline's 44 MJ/kg) and require higher injection volumes to maintain power, which may result in higher average in-cylinder temperatures and an increase in the overall heat load of the engine (especially under high load conditions).
Some biofuels (e.g. unrefined biodiesel) may produce more deposits after combustion, adhering to the piston, cylinder liner and other components, reducing the thermal conductivity, indirectly leading to higher local temperatures, requiring the cooling system to have a stronger "targeted heat dissipation" capability.
Corrosiveness and Impurities
Biofuels (especially biodiesel that is not fully esterified) may contain free fatty acids, long-term operation may lead to slight corrosion of engine cooling circuits (such as cylinder water jacket), the cooling medium needs to be added to the anticorrosive agent, and at the same time, the piping / core material of the dry cooling system needs to be corrosion-resistant (e.g., using aluminum alloy, stainless steel).
Dry cooling system (also known as dry cooler system) is a closed loop cooling device with air as the cooling medium, through the direct heat exchange between the air and the circulating medium (usually water or glycol solution), to achieve the cooling of the engine. For internal combustion engines using biofuels (e.g. biodiesel, ethanol, biogas, etc.), due to the differences in combustion characteristics with conventional fuels, the dry cooling system needs to be optimized to meet the heat dissipation requirements and adapt to the special working conditions of biofuels.
The core of the dry cooling system for biofuel internal combustion engines is to transfer the heat generated by the engine to the dry cooler through a closed loop, and then dissipate the heat through the air. The structure of the system is similar to that of a traditional dry cooler, but it needs to be adapted to the above-mentioned heat dissipation characteristics:
Core Components
Circulating fluid circuit: a closed circuit driven by a water pump, the fluid (water + glycol mixture, anti-freezing and with increased boiling point) flows through the engine water jacket, oil cooler and other components, absorbing heat and then entering the dry cooler.
Dry cooler core: the core heat transfer unit, mostly plate-fin or tube-bundle structure, the internal circulation of high-temperature work material, the external fan forced ventilation or natural wind to take away the heat. For the high load of biofuel engines, the core is usually designed with a larger heat transfer area (10%-20% more than traditional systems) and adopts high-density heat sinks to improve efficiency.
Fan and control system: Equipped with variable frequency fan, it can automatically adjust the speed (e.g. increase the speed when the temperature exceeds 90℃) according to the temperature of the work material at the outlet of the engine (monitored by sensors), so as to avoid overheating caused by insufficient heat dissipation of the biofuel engine when it is under high load.
Expansion tank and filter: the expansion tank balances the volume change of thermal expansion and contraction of the mass; the filter is used to intercept the trace impurities (such as carbon particles) that may be generated by the combustion of biofuel to prevent clogging of the core of the dry cooler.
Workflow
High-temperature work material (about 80-100 ℃) from the engine out into the dry cooler core;
core outside, fan-driven cold air (ambient temperature) flows through the heat sink, and the work material for heat exchange (air temperature rises, the work material temperature down to 60-80 ℃);
cooled work material through the pump back to the engine, the cycle of heat dissipation;
control system real-time monitoring of the work material temperature and engine load, dynamic adjustment of fan speed and water flow The control system monitors the work material temperature and engine load in real time, and dynamically adjusts the fan speed and water pump flow to ensure that the biofuel engine is at the optimal working temperature (usually 85-95℃) under different working conditions such as idling, heavy load and so on.
