The quality of an engine is determined by these indicators.

In automobile theory, there are a series of indexes to evaluate engine performance, such as power index, economy index, reinforcement index, compactness index, environmental index, reliability index, durability index, manufacturability index, speed characteristics of internal combustion engine and so on.

These performance indicators are used to characterize the performance characteristics of engines and serve as the basis for evaluating the performance of various engines. Let’s talk about the specific meaning of these indicators.

Power performance index is an index to characterize the engine’s working capacity. Generally, the effective power, effective torque, average effective pressure and engine speed of the engine are used as indicators to evaluate the engine’s power performance.

1. Effective power:Effective power refers to the effective work output by the engine in unit time, which is what we often call the power of the engine.

It is the most important index of engine performance, which is directly proportional to the effective torque and engine speed. The engine power on an automobile is marked with total power and net power.

The total power refers to the power generated by the engine without any auxiliary equipment, while the net power refers to the power output from the flywheel with all auxiliary equipment including the generator, water pump, fan, steering booster pump and air conditioning compressor. Obviously, net power is more practical to us.

2. Effective torque:Effective torque refers to the torque output from the flywheel of the engine, which is what we often call the torque of the engine. Generally, the greater the torque of an engine, the stronger its acceleration and climbing ability.

The earlier the maximum torque of the engine appears and the wider the continuous speed range, the better the power performance of the car. Generally, high-torque engines are characterized by large cylinder bore and long stroke, and such engines generally have large displacement, so some old drivers often say that "displacement is king", and the larger the displacement, the more energetic it is. This is the truth.

3. Average effective pressure:The average effective pressure refers to the effective work issued by the working volume of the unit cylinder, that is, the force that pushes the piston downward. Generally, the greater the average effective pressure of the engine, the stronger the working function of the engine, and the greater the maximum power and torque.

4. Engine speed:Engine speed refers to the number of revolutions per minute of the engine crankshaft. The higher the engine speed, the more times the engine does work per unit time, and the greater the engine power.

For example, compared with a diesel engine, the maximum torque of a gasoline engine is not as large as that of a diesel engine, but the maximum power is higher than that of a diesel engine, which is due to the higher rotational speed of the gasoline engine.

In addition, the same kind of engine is also divided into two types: low-speed engine and high-speed engine. Therefore, when explaining the effective power of the engine, the corresponding speed must be indicated at the same time.

It must be noted here that the power of the engine is not equal to the power of the car, and the power of the engine is not equal to the power of the car. The dynamic performance of a car refers to the maximum speed, acceleration time and maximum climbing degree of the car, which is a comprehensive index.

Engine economy index includes two indexes: effective thermal efficiency and effective fuel consumption rate.

1. Effective thermal efficiency:The percentage of heat generated by fuel combustion converted into effective work is called effective thermal efficiency. Obviously, the higher the effective thermal efficiency of an engine, the better its economy.

At present, the thermal efficiency of gasoline engines is generally between 30% and 38%, but the thermal efficiency of diesel engines is higher than that of gasoline engines, which can generally reach 35% to 45%. The efficiency of electric vehicles can be as high as 90% or even 100%. Therefore, many countries are supporting the development and research of new energy vehicles and gradually restricting the production of fuel engines.

2. Effective fuel consumption rate:The amount of fuel consumed per 1kw of effective work output by the engine is called effective fuel consumption rate.

Obviously, the lower the effective fuel consumption rate of an engine, the better its economy. Generally, the effective fuel consumption rate of an engine is about 20g/kW h, that is, when the engine works for one hour and emits one kilowatt of power, it needs to consume about 20g of fuel.

Here, we should also pay attention to distinguish the economy of the engine from the economy of the car. The economy of a car refers to the fuel consumed by a car for a certain mileage, which is related to many factors. Good engine economy is only one of them, which does not mean that a good engine economy is necessarily good.

The reinforcement index refers to the evaluation index of the engine’s ability to withstand thermal load and mechanical load, which generally includes the power rise and reinforcement coefficient.

1. Power rise:The effective power output per unit engine displacement is called rising power when the engine is in calibration condition. The greater the lift power, the greater the effective power per liter of cylinder working volume, and the higher the thermal load and mechanical load of the engine.

Generally, the more advanced the engine, the higher the power. The engine with supercharging technology also has higher power rise than the naturally aspirated engine.

2, strengthening coefficient:The product of the average effective pressure and the average piston speed is called the reinforcement coefficient. The average piston speed refers to the average reciprocating speed of the piston when the engine works at the rated speed.

Obviously, the higher the reinforcement coefficient of the engine, the better its power performance, but the higher the requirements for the mechanical strength of the engine.

Compactness index is an index used to characterize the compactness of the overall structure of the engine, which is usually measured by specific volume and specific mass. Specific volume refers to the ratio of engine profile volume to its rated power, and specific mass refers to the ratio of engine dry mass (dry mass refers to the engine mass without fuel and coolant) to its rated power.

Obviously, the smaller the specific volume and specific mass of the engine, the more compact the engine structure.

Environmental indicators are used to evaluate engine exhaust quality and noise level. Exhaust quality refers to the amount of pollutants in engine exhaust, which is directly related to the living environment and health of human beings. At present, automobile exhaust pollution is an important factor of air pollution, so governments all over the world have formulated strict control laws and regulations to reduce the environmental pollution caused by engine exhaust and noise.

Reliability index is an index to characterize the normal and continuous working ability of the engine under the specified use conditions. The indicators for evaluating reliability include the mileage of first failure, the average mileage between failures, the damage rate of main parts, etc. This indicator is obtained by monitoring the whole life cycle of the engine.

Generally, it is bathtub-shaped, so it is also called "bathtub curve". At the initial stage of use, the failure rate is high, then the failure rate gradually decreases, and then it remains at a low level for a long time, and then the failure rate suddenly rises and remains high. At this time, the car will reach the end of its life.

Durability index refers to the limit time when the main parts of the engine are worn to the point where they cannot continue to work normally. It is usually measured by the mileage of engine overhaul, that is, the mileage traveled by the car between the factory and the first overhaul.

The manufacturability index refers to the index to evaluate the manufacturability and maintenance manufacturability of the engine. The engine structure has good manufacturability and is convenient for manufacturing and maintenance, so the production cost and later maintenance cost can be reduced.

This should be "painful" for many repairmen. Some engines are so compact that even if a small part is changed, many accessories have to be dismantled to do it. This kind of engine can be said to have poor manufacturability.

The relationship between engine performance indexes and adjustment conditions and operating conditions is called engine characteristics. There are speed characteristics, load characteristics and universal characteristics for gasoline engines.

The relationship between the effective power, effective torque and effective fuel consumption rate of the engine and the engine speed is called the speed characteristic of the gasoline engine. When the engine speed is fixed, the relationship between the fuel consumption per hour and the effective fuel consumption rate changes with the load is called the load characteristic of gasoline engine.

Universal characteristic curve is to synthesize multiple performance curves of the engine on a coordinate diagram, and comprehensively describe various performances of the engine. From the universal characteristic curve, we can see the running relationship of the engine at any speed and load, and can make economic analysis.

The speed characteristic of the engine is a very complicated concept. Analyzing it can deeply understand the relationship among engine power, torque and fuel consumption, which is of great guiding significance for us to know the engine and use it better.

The above are the main indicators to evaluate the performance of the engine. In fact, these indicators are a bit too academic. It is impossible for us ordinary consumers to understand all these indicators, and it is impossible for automobile manufacturers to mark all these indicators. So how can we judge the quality of the engine by simple methods when buying a car?

Generally speaking, we can look at the characteristic curve of the engine, which can clearly see the power output characteristics of the engine, see what the speed of the maximum torque of the engine is, how big the continuous speed range is, the economic working range of the engine, and so on.

Another situation is that we buy it. How can we identify the quality of the engine? This requires a wealth of experience, and it is difficult for an ordinary person to identify the advantages and disadvantages of engine performance.

Generally speaking, we can observe from several aspects:

First, whether the engine runs smoothly and whether the acceleration is smooth;

The second is the exhaust emission of the engine and the color of the exhaust gas. For example, if the exhaust gas temperature is too high, it means that the combustion is not good, if the exhaust gas is blue, it means that the engine works irregularly, and so on.

The third is to observe the lower exhaust of the engine. If the lower exhaust is too large, the engine is seriously worn. The fourth is to observe the carbon deposition inside the exhaust tailpipe. It is dry and has no carbon deposition under normal conditions. If there is a large amount of black carbon deposition, the engine will not burn well. If there is oil stain, the engine oil consumption is too large, and so on.(Text/KajiaNo.: Lao Hou Jie Che)