求翻译：2、忌长期使用。火花塞型号繁多，但都有自己的经济寿命、如果超过经济寿命后仍然使用，将不利于发动机的动力性和经济性的发挥。有研究表明，随着火花塞使用期的延长，其中心电极端面会向圆弧形状变化，侧电极则向凹弧形状变化，这种形状将使电极间隙增大，并造成放电困难，影响发动机的正常工作。是什么意思？

2, avoid long-term use. Spark plug model range, but has its own economic life, if even after use over economic life, will be detrimental to engine power and economy of the play. Studies have shown that with the spark plug to use the extension period, the center electrode to the circular shape of the

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2, avoid long-term use. Spark plug model range, but has its own economic life, if more than the economic life remains after use, will not be conducive to the engine power and economic nature of the play. Research has shown that, with the spark plug extension of period of use, extreme surface ECG wil

2, avoid long-term use. Spark plug model range, but has its own economic life, if more than the economic life remains after use, will not be conducive to the engine power and economic nature of the play. Research has shown that, with the spark plug extension of period of use, extreme surface ECG wil