What Are the Factors that Affect the Low Working Temperature of Spark Plugs in Fire Fighting Trucks?

The working environment of spark plugs is extremely harsh, as they have to withstand high temperatures, high pressures, and corrosive exhaust gases after combustion. Nevertheless, the working temperature of spark plugs cannot be too low. If the temperature is too low, the insulation material on the spark plugs is prone to carbon buildup, which eventually leads to misfires due to electrical leakage. At this time, we need to understand the reasons for the low working temperature of spark plugs in firefighting trucks and take measures to prevent it.

Firefighting trucks basically have two main functions for spark plugs: sealing the spark plug hole to maintain cylinder pressure and generating sparks in the combustion chamber to ignite the fuel mixture and generate power. Usually, high voltage electricity of about 20,000 to 30,000 volts is supplied to the spark plug from the ignition coil through the distributor cap and the wire. Additionally, the spark plug electrode must be constantly in a high-temperature combustion chamber with an environment of over 45 times atmospheric pressure, and it must maintain high airtightness. Therefore, in such a harsh environment, the quality and durability of spark plugs will directly affect the performance of the engine, so they should not be overlooked. The factors that affect the low working temperature of spark plugs in firefighting trucks are as follows:

Improper selection of spark plugs for firefighting trucks

Different cold and hot models of spark plugs have different heat dissipation speeds. Cold-type spark plugs dissipate heat very quickly, while hot-type spark plugs have a relatively slow heat dissipation speed. To ensure stable operation of the spark plugs at the specified temperature, cold-type spark plugs must be used for engines with high compression ratios and high calorific values to increase heat dissipation speed. Conversely, hot-type spark plugs should be chosen for engines with low calorific values. If a cold-type spark plug is still chosen for an engine with low calorific value, the working temperature of the spark plug in the firefighting truck will inevitably be too low to clean itself.

Carbon buildup on spark plugs in firefighting trucks

Fuel composition affects carbon buildup on spark plugs. For example, the higher the proportion of olefins in fuel composition, the easier it is to have incomplete combustion, resulting in carbon buildup on spark plugs. If the fuel mixture is unevenly mixed, especially in direct injection engines, incomplete combustion can easily occur, leading to carbon buildup on spark plugs. If the ignition coil is abnormal or the ignition energy is insufficient, incomplete combustion or misfires may occur, resulting in carbon buildup on spark plugs which is not easy to remove. When the working temperature of the spark plug is lower than the self-cleaning temperature, the spark plug cannot reach the conditions for self-cleaning, and the resulting carbon deposits will accumulate on the ceramic insulator of the spark plug and cause short circuits.

Environmental temperature also affects spark plugs in firefighting trucks

When the firefighting truck engine is working in summer, carbon buildup on spark plugs is not easy to occur. In addition, in northern regions, the average working temperature of the same engine in winter is 5-10 °C lower than in summer. Therefore, when selecting spark plugs, a hotter type of spark plug should be chosen for winter use.

Incorrect installation of spark plugs in firefighting trucks

In order to prevent air leakage between the spark plug and the cylinder, firefighting trucks sometimes add seal gaskets to the spark plug indiscriminately, leading to a decrease in the tightening force of the spark plug and damage to the threads. Also, the contact area between the spark plug and the cylinder increases, which increases the heat dissipation speed of the spark plug, causing the working temperature of the spark plug to be too low.

If the working temperature of the spark plug is inappropriate, the firefighting truck may experience a lack of power, increased fuel consumption, unstable engine operation, and emission of smoke from the exhaust. Therefore, we recommend that firefighters regularly maintain spark plugs, and most importantly, choose appropriate spark plugs.