Will the normal use of automobile air conditioning system increase fuel consumption?
This question is one of the few questions with standard answers in the automobile field: cold air conditioning will increase fuel consumption, warm air system will not affect fuel consumption, and the influence of windshield size on fuel consumption can be ignored.
I. Air volume &; oil consumption
The "fan" in automobile air conditioning system is essentially a fan or blower. The greater the air volume, the higher the power consumption naturally. Because high speed requires high power output of motor, increasing power under constant torque turntable can only improve speed.
The law of conservation of energy is the law of nature. If you want to get higher power (kinetic energy), you must consume enough energy. However, the circuit system of the car is extremely redundant. On the premise that the power generation far exceeds the electricity consumption, these electric energies seem to be "useless, useless, useless".
Knowledge point 1: After the car is started, the engine drives the generator to keep running. At this time, the battery no longer supplies power to the car, and the motor will charge the battery while supplying power to the equipment.
The power standard of the original car generator is generally 1000/ 1500 watts (w), and its concept is to run at rated power, which can generate electricity 1.0~ 1.5 degrees per hour. The power of air-conditioning fans in cars is often only about 50 watts. Even if there is a front and rear independent air supply system, how many watts can the comprehensive power be?
Knowledge point 2: the power of the main electronic equipment of the automobile is very small. For example, the speaker (sound system) with the highest power consumption is only two or three hundred watts, and the power of dashboard and navigation machine is much lower; As for the battery capacity, it is actually only about 0.5~0.7 kWh, so the fuel consumption of these devices will not fluctuate obviously during normal operation.
Or the generator is connected with the crankshaft of the engine through a belt. This setting has calculated the influence of power consumption on fuel consumption, and normal electronic equipment is really unnecessary.
Second, the cold wind-affecting fuel consumption
The basis of automobile air conditioning refrigeration is "compressor+refrigerant", and tetrafluoroethane is widely used as refrigerant; Its characteristic is that the boiling (gaseous) temperature is as low as -26.2℃. The compressor presses gaseous tetrafluoroethane into the condenser, and after drying and expansion valve, it becomes a liquid with lower temperature.
When the evaporator finally reaches above zero, it will boil instantly and absorb heat energy during evaporation and boiling. After the evaporator is passively cooled, the fan will blow hot air through the evaporator. Based on the principle that low-temperature objects will absorb heat and cool air, what is sent into the car is cold air.
To put it bluntly, refrigeration is the use of two endothermic:
1, refrigerant absorption evaporator temperature
2. The evaporator absorbs the heat energy of the air.
But the essence is that tetrafluoroethane can circulate in the pipeline, but this high-pressure gaseous substance needs a lot of driving force to run. The force exerted by an ordinary car is about "5PS horsepower", which is about 3kw. If it is driven by electricity, it is the standard of 3 degrees per hour. However, the compressor of the fuel truck is connected with the crankshaft of the engine through a belt. After the AC switch is turned on, the belt compressor is sucked by its pulley, and as a result, it will consume about 3kw of power.
If the power of the car is obviously reduced, the acceleration ability and speed will be reduced. The only way to reach the standard before turning on the air conditioner is to increase the speed and output power. High speed equals high frequency fuel injection, so fuel consumption will always be high when driving in summer.
Third, warm air-no effect.
The type of engine equipped with fuel vehicles is "internal combustion engine", and its working principle is that burning fuel generates heat energy, which drives the piston, connecting rod and crankshaft to move into mechanical energy (power). This operation mode will produce very high temperature, for example, the flame temperature of gasoline combustion is as high as 1200℃, so it is necessary to use water cooling system to circulate heat dissipation when the engine block does not melt.
The function of antifreeze coolant is to adjust the temperature of the engine during circulation, and the temperature will reach about 100℃ when the engine is hot. So this high-temperature solution is also used as "water-cooled air conditioner", and the concept is as follows.
Note: When the air conditioning fan is turned on, the heater may not start. The temperature must be adjusted to the high temperature standard or the red indicator light, and then the valve of the water cooling system is opened, and the high-temperature antifreeze coolant will flow into the heater box for heating. When the water tank is hot enough, the blower blows low-temperature air through the evaporator to raise the temperature.
Low temperature air absorbs the heat energy of water tank-heating.
The temperature of the water tank can be reasonably controlled.
The principle of heat absorption is inseparable from the automobile heating and cooling system, which is also in line with the explanation made by the second law of thermodynamics. However, this kind of heat energy is "waste heat", just like it is a truth that excess electric energy is not wasted, but why does the fuel consumption increase in winter?
Fourth, the reason-hot car efficiency
Engine thermal efficiency is the basis of judging fuel consumption. Its concept refers to how much of the total thermal energy generated by combustion can be converted into mechanical energy. 40% thermal efficiency means wasting 60% and using 40%. See?
Key points: the best thermal efficiency needs the best operating temperature, which is about100℃; However, the body and antifreeze coolant will cool down after long-term parking, and the standard is the same as the ambient temperature.
The summer temperature is 40℃- the temperature difference is about 60℃
Winter temperature ≤0℃- temperature difference exceeds 100℃.
The greater the temperature difference, the slower it is to reach the ideal temperature. At the same time, the running low-temperature air will absorb heat energy, so the heating speed will be slower. At this stage, the thermal efficiency will be much lower, a larger proportion of thermal energy will not be converted into torque, and the output power will naturally be lower. If you want to improve power and speed, you have to increase speed, but the fuel consumption will be abnormal.
In the same cold start, ECU will actively increase the fuel injection quantity and fuel injection speed, with the aim of burning more fuel (generating more heat energy), so as to achieve the purpose of rapid warm-up. When idling, the fuel injection will be doubled, and if you have the habit of heating in place, the fuel consumption will be high.
However, the low temperature in the car in winter will affect the driving experience, so many users who know that the hot car is not in place have to do so. This is the main reason for the increase of fuel consumption in winter, which is a normal physical phenomenon and has nothing to do with the air conditioning system.