The right spark plug can eliminate idle misfires

16 January 2018 | Article

According to the New European Driving Cycle (NEDC), the average passenger car idles for 22.6% of the time when in use.

According to the New European Driving Cycle (NEDC), the average passenger car idles for 22.6%¹ of the time when in use. When a car idles, it burns fuel as the engine does not have to deliver any power to the wheels. Thus, to keep losses to a minimum, the idling speed is set to a low rpm, minimizing the fuel amount needed to keep running.

However, running an engine made to deliver power at such a low rpm is difficult and increases stress on the spark plug especially. Due to the low power required, only minimum amounts of air and fuel are supplied to the engine, resulting in low amounts of potential air/fuel mix near the spark plug. The gas flow speed inside the combustion chamber is also very low, which makes ignition more difficult and increases the need for high performance spark plugs.  

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Spark plug trial

The HAN Automotive Institute at HAN University, Arnhem, Netherlands, studied this phenomenon. In a 2016 study, researchers tested and compared DENSO spark plugs against competitor spark plugs, using a test bench with an Opel 1.4 engine, and counted the average number of engine misfires when idling. 

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While competitor nickel spark plugs averaged 17.7% misfires, compatible DENSO KJ20PR-L11 averaged only 12.5%. This average decreased dramatically when upgraded DENSO spark plugs were used. The Nickel TT spark plug K20TT only had a 0.5% average misfire rate while both the Iridium Power IK20L and Iridium TT spark plug IK20TT had zero misfires during the trials.²

Misfire count – what does it mean for the vehicle?

A low misfire count results in a smooth and stable idling engine that is easier to start, especially important for vehicles with stop/start systems, and lowers fuel consumption as less fuel is wasted, resulting in cleaner emissions.

“Most modern ECUs can detect misfires and will compensate for them with a slightly increased idling speed,” said Gilbert Couvert, Product Manager, Spark Plugs at DENSO Europe Aftermarket.

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“But when a vehicle uses upgraded TT spark plugs like the DENSO Nickel TT spark plug K20TT and Iridium TT spark plug IK20TT, the idling speed can be lowered, thus further decreasing fuel consumption and vehicle emissions.”

 In engines with a turbocharger and in engines with fewer cylinders such as motorcycles and modern downsized vehicles, achieving a smooth idle is even more difficult, thus making high performance spark plugs even more of a necessity.


¹https://www.dieselnet.com/standards/cycles/ece_eudc.php
²Test conditions:
Opel Z12XEP engine, BY 2009
Idle set to 850 rpm;Closed tumble valve
Misfire @ peak pressure < 8bar
Counted over 3 x 164 cycles
Spark plug gap 1.1mm
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