For most passenger cars on the market, the spark plug replacement mileage specified by the naturally aspirated engine is generally 40,000 kilometers, and even 80,000 kilometers need to be replaced.
However, if the engine has turbocharging and in-cylinder direct injection technology, the spark plug replacement cycle required by the manufacturer will be greatly reduced, and it is not a few to replace it at 40,000 kilometers, and even more so, some models need to replace the spark plug at 20,000 kilometers. Why is the spark plug replacement cycle in a turbocharged engine so short? Is it because the manufacturer cuts consumers as leeks in order to overcharge maintenance costs? Actually, no, this has to start with the technology of the engine.
The higher the ignition energy, the shorter the lag period and the lower the risk of pre-ignition
The lower the ignition energy, the longer the lag period, and the greater the risk of premature ignition, which will induce detonation
Ignition energy/number of times to increase the consumption of electrodes
Early fans of automobiles may know that the ignition coil of some engines uses a single-point ignition coil plus distributor configuration, that is, all cylinder spark plugs share a single ignition coil. In the case of a four-cylinder engine, for example, only one spark plug is effectively ignited when ignition, and the rest of the cylinders are invalid ignited. This type of ignition has a breakdown voltage of the spark plug ranging from a few thousand volts to 20,000 volts.
Later, the engine performance is getting higher and higher, in order to ensure the normal operation of the electronic control system and reduce electromagnetic interference, simply cancel the distributor and high-voltage wire, and equip each cylinder with an independent ignition coil, the ignition coil is directly installed on the top of the spark plug, and the energy conduction loss and leakage loss are very small. The main thing is to greatly increase the breakdown voltage of the spark plug, ranging from about 1-40,000 volts, which further improves the performance of the engine.
Later, in order to achieve more efficient and high-energy ignition, some high-performance engines (such as Mercedes-Benz's V12 engine) even arranged two spark plugs for each cylinder to meet the ignition needs. However, during maintenance, replacing 24 spark plugs at a time is really a headache, with high technical difficulty and high maintenance costs, and it is not suitable for ordinary civilian vehicles.
In recent years, some engines have begun to be equipped with multi-point ignition technology, that is, the ignition coil supplies power and ignition to the spark plug multiple times in one work cycle. For example, Mercedes-Benz's M274 is equipped with fast multiple discharge ignition technology (MSI), which is followed by a rapid combustion process after the first spark discharge, the ignition coil is immediately charged to complete the second spark discharge, and within one stroke, five fuel injections are completed, and four electric sparks are released within 1 millisecond, of course, the loss of the spark plug also increases exponentially. Others, such as BMW, also have similar technology.
In addition to the multiple ignition method, increasing the ignition energy is also one way. According to the data of Changan Automobile, the ignition energy of the traditional automobile engine is generally about 90mJ, which is increased to 150mJ, which can form a larger size of the initial fire core, which is more conducive to the formation of a stable and fast initial velocity laminar flow propagation flame, combined with the tumbling flow in the cylinder, to achieve the rapid propagation of the pre-combustion mixture in the cylinder, and improve the thermal efficiency.
One plus one minus electrode consumes more
Two conductors close to each other, sandwiched between a layer of non-conductive insulating dielectric, constitute a capacitor. There is resistance in spark plugs, and the effect of resistance can suppress electromagnetic interference during ignition, but high or low resistance is a double-edged sword. If the resistance is too high, part of the ignition energy will be consumed, and the ignition energy will be weak, and if the resistance is too low, the ignition energy will be greater, but the current and voltage that the electrode is easy to withstand will be greater, and the electrode loss will be larger.
At the same time, the engine with turbocharging technology has a higher operating temperature and a higher temperature of the spark plug, which leads to a decrease in the insulation resistance of the ceramic skirt, while the resistance of the metal increases with the increase in temperature, increasing and decreasing, making it easier to penetrate the ceramic insulator.
In addition, the current engine is becoming more and more compact and lightweight, and the thread diameter of the spark plug has also changed from the previous M14 to M12 or even smaller, which makes the diameter of the ceramic insulator thinner. In other words, insulators are thinner and less resistant to fabrication, which also makes ceramic insulators more prone to breakdown failure.
The impact of carbon deposits
No matter what the model is, there must be more or less carbon deposits. The carbon deposits at the spark plug will disperse and reduce the ignition energy, increasing the misfire rate (engine misfire, which refers to the failure or insufficient work of one or several cylinders of the engine, which is what we usually call "engine cylinder shortage"). After the engine misfires and fails, there will be serious shaking, the engine power is insufficient, the acceleration of the car is weak, and the fuel consumption is high), so that the ignition energy becomes lower, the lag period becomes longer, and the electrode and ceramic body are lost at an accelerated rate.
In addition, it increases the risk of premature ignition, which can cause detonation. Here you can keep the spark plug clean by adding gasoline cleaner regularly.
Afterword
At present, the vast majority of spark plug electrodes are made of precious metal materials, although there will be no problem of excessive electrode consumption in the life cycle, but under the above multiple factors, the gap size of the spark plug is no longer the basis for judging its life cycle. The manufacturer's request for 20,000 kilometers to replace the spark plug is by no means an attempt to cut the consumer's leeks, but a conclusion obtained after long-term reliability testing. Of course, you can be reluctant to, or learn from the ignorant experience of some "old" drivers, once the spark plug burns out, it is not a joke.