DENSO has started to sell IRIDIUM TT spark plugs having a φ0.4 mm iridium alloy center electrode and a 0.7 mm needle-type platinum alloy ground electrode.
The quenching effect has been decreased by forming the electrode into a double needle shape. As a result, the flame kernel rapidly develops and the engine's power is drawn out to its maximum potential.
➊Built-in, Highly Reliable Resistor
All specification types include an embedded, highly reliable, monolithic resistor to eliminate electoromagnetic noise interference from all kinds of electronic devices. ➋360° Laser Welding
The iridium tip is mounted with an "All-around Laser Welding" method that insures high reliability even under the most severe driving conditions. ➌φ0.7mm Needle-Shaped Platinum Ground Electrode
In order to maximally prevent quenching effect, the ground electrode needs to be made as small as possible. Traditional ground electrodes could not be made too small without reducing groundig strength or increasing electrode wear.
However, we've managed to attach a fine 0.7mm-diameter platinum electrode using a 360° laser welding technique. ➍φ0.4mm Ultra-fine Iridium Center Electrode
Using DENSO's exclusive iridium alloy having a very high melting point, the tip of the center electrode can be shaped very thin and fine, reducing spark voltage requirements and greatly improving ignitability.
The photograph shows flame reflected by the variation in density. Fig. 1 shows the results of studying the influence of electrode shape on flame growth, using the Iridium Spark Plug and IRIDIUM TT.
The photographs indicate that, in the case of the Iridium Spark Plug, the size reduction of the gap (from 1.1 mm to 0.6 mm) interfered with flame growth, while in the case of IRIDIUM TT, flame growth was ample and greater than that of the Iridium Spark Plug in spite of the narrowed spark gap (0.6 mm). These observations show that, as the results of the ignition/firing simulation indicated, a fine ground electrode can reduce required voltage because it enables the spark gap to be narrower, while realizing higher ignitability than the Iridium Spark Plug.
Advantages of Fine Ground Electrodes
To lower the required voltage and improve firing performance. The most advanced technology in the world has been employed to enable use of electrode, at 0.4 mm in diameter, in the IRIDIUM TT.
The smaller the electrode the more concentrated the electric potential at the tip of the electrode and the stronger the electric field that affects required voltage and the lower the required voltage. As a result, combustion is good for all types of driving, the engine starts easily, and acceleration improves.
The above shows the strength of electrical field in case certain voltage changes on Iridium plug and IRIDIUM TT.
The more electrical field strength is getting high, the more it becomes easy to fire with low voltage.
*1 FEM(Finite Element Method analysis): General method to measure electrical field strength.
Fig. 3 shows the results of evaluating how the miniaturized-portion protrusion direction may influence the ignitability of an engine. The evaluation checked idle speed at equal throttle opening with the ISC (idle speed control) turned off. A higher idle speed represents higher ignitability.
This figure shows the results of evaluating IRIDIUM TT. This figure shows that IRIDIUM TT are superior to the Iridium Spark Plugs in ignitability.
Better fuel efficiency
Fig. 4 shows the results of the examination of combustion variation and fuel consumption, using a 1,800-cc, four-cylinder engine. The evaluation was conducted by turning on the ISC and setting the average engine speed to 800 rpm (idling). The previously specified Type-1 of the IRIDIUM TT was used in this examination. Pmi COV (coefficient of variation) in the diagraph shows fluctuation in IMEP (indicated mean effective pressure). As this figure shows, IRIDIUM TT can reduce the Pmi COV approximately 3.1% and accordingly reduce fuel consumption by 2.4%, compared with the Iridium Spark Plug. These advantages are achieved because the miniaturization of the ground electrode enables better ignitability, improving combustion efficiency. Because the IRIDIUM TT is low in combustion variation and enables a reduction in idling speed, further improvement can be expected in fuel efficiency.