Search Results

Improving the engine efficiency to respond to climate change and energy security issues is strongly required. In order to improve the engine efficiency, lower fuel consumption, and enhance engine performance, OEMs have been developing high compression ratio engines and downsized turbocharged engines. However, higher compression ratio and turbocharging cause cylinder pressure to increase, which in turn increases the demand voltage for ignition. To reduce the demand voltage, a new ignition system is developed that uses a high voltage Zener diode to maintain a constant output voltage. Maintaining a constant voltage higher than the static breakdown voltage helps limit the amount of overshoot produced during the spark event. This allows discharge to occur at a lower demand voltage than with conventional spark ignition systems. The results show that the maximum reduction in demand voltage is 3.5 kV when the engine is operated at 2800 rpm and 2.6 MPa break mean effective pressure.

An ignition simulation and an ignition visualization method that analyze effects of spark plug electrode design have been developed. In the ignition simulation, a programmed heat source corresponds to the discharge energy in the spark gap, and the flame-kernel generation and flame propagation are calculated on the heat balance in the gap, in consideration of thermal transmission to the electrodes. The results by this simulation indicate that high ignitability of fine ground electrode spark plugs is because the miniaturization of the ground electrode reduces the heat loss, and flame growth is thus less disturbed by the loss. The ignition visualization includes taking Schlieren images by laser light to capture flame kernels with weaker luminescence intensity compared to ignition discharge spark luminescence. This visualization enables the observation of the influence of the shape of spark plug electrodes on flame growth.

Spark plugs with higher ignitability are continuously in great demand to realize high fuel efficiency and low emissions. To meet this demand, DENSO launched the Iridium Spark Plug in 1997, which realized the two characteristics that had been conventionally difficult to achieve concurrently-high ignitability and long life. The development of this product was enabled by miniaturizing the center electrode, produced using DENSO's original, highly wear-resistant iridium alloy (featuring a high melting point and excellent oxidation resistance). While spark plugs are now required to have a longer service life, they are also required to be higher in ignitability, as exhaust gas regulations have been tightened recently. However, the effort to miniaturize the center electrode is reaching a limit.

Fatigue life of the 6206 deep groove ball bearings has been evaluated under various thin lubricant film conditions. Endurance testing demonstrates that the fatigue life is remarkably longer than previous formal experiments. In addition, examination of flaked areas showed some to have subsurface origins, even after testing with extremely thin lubricant films. Longer fatigue life has been attributed to improvements in bearing steel quality, as well as improvements in the surface roughness of the ball bearing raceways. With thin lubricant films, the film parameter Λ, and the roughness profile have a greater influence on ball bearing fatigue life. Qualitative analysis of the rolling contact surfaces of some of the bearings after test has been carried out, and the formation of oxidized and carbonated films has been detected. These films can be considered to be contributors to longer fatigue life.