You have probably used a Piezo device to light your barbeque, gas stove, or oxy torch but what's that have to do with the automotive world?
As with the barbeque lighter, a button is pushed resulting in the flexing of a small crystal. This crystal movement creates a high voltage which is released as a spark. This process can be done in reverse where a high voltage is applied to the crystal, causing a small amount of movement. This process has been developed to the extent where it can be used to control an injector, opening enough to allow a very controlled amount of fuel to pass.
Currently, these injectors operate in diesel engines employing common rail (CR) technology of roughly 1800 bar pressure ( 26,000psi). The injectors can operate four to five times faster than servo-hydraulic CR injectors. This speed, combined with a more sophisticated electronic management, allows far greater control of the injection process. The BOSCH Piezo CR system can handle up to seven injection pulses per cycle, giving the option of having small "pre" and "post" injections in addition to the main injection, resulting in improved performance and economy. Benefits of using Piezo CR injectors are:
- Enhanced multiple injection capabilities.
- Increased fuel economy.
- Increased power and torque.
- Cleaner exhaust emissions.
- Reduced engine noise.
- Very consistent performance over the injector life.
While the price of Piezo CR injectors is much higher than conventional CR injectors, benefits out weigh the costs. If injectors do require replacement, the individual injector characteristics need to be taken into account. Each injector is coded and this information needs to be downloaded into the ECU, where a compensation factor is applied.
Safety precautions are required when working with any common rail fuel system. Remember the system operates under extremely high pressure. Do not loosen an injector pipe to test for fuel delivery as this may result in injury or death. Piezo injector systems operate on higher voltage than conventional CR systems, around 150 volts, so additional precautions are required.