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Piezo Injectors: The Rise, The Fall, and The Lessons Learned

Writer's picture: Melanie BatesonMelanie Bateson

by Alex Topin, BM-Tech

Piezo injectors – once considered a revolutionary breakthrough in fuel injection technology – have had quite a journey in the automotive world. From their promising debut to their eventual decline in gasoline engines, the story of piezo injectors is a fascinating tale of innovation, challenges, and practical realities. While they still have their place in some applications, they’ve taught the automotive industry an important lesson: advanced technology isn’t always the best solution for every scenario.

What Are Piezo Injectors?

Piezo injectors are a type of fuel injector that utilises the piezoelectric effect – a phenomenon where certain materials generate an electrical charge when subjected to mechanical stress. This effect can be reversed, allowing these materials to change shape or deform when voltage is applied. By harnessing this property, piezo injectors can achieve ultra-fast response times, incredible precision, and multiple injection events in a single engine cycle.


Piezo Injectors by Alex Topin for BM Tech

The Initial Success of Piezo Injectors

These qualities made piezo injectors a game-changer when they first appeared in gasoline engines. Compared to traditional solenoid injectors, which rely on electromagnetic force to operate, piezo injectors were touted as superior in every way. Their lightning-quick response times – as low as 0.2 milliseconds – made them ideal for advanced fuel injection strategies like stratified injection, which delivers multiple, precise fuel doses during a single stroke, improving combustion efficiency and reducing emissions.

At first, the automotive world was excited. Mercedes-Benz pioneered the use of piezo injectors in its CLS 350 models, while BMW adopted them for its N54 engine, followed by early versions of the N55 and N63 engines. Engineers believed that piezo injectors were the future of fuel injection systems, especially for high-performance and luxury vehicles where cutting-edge technology is a key selling point.

Why Did Piezo Injectors Fail in Gasoline Engines?

Despite their impressive advantages, piezo injectors quickly proved to be problematic in real-world applications, particularly in gasoline engines. Several key factors led to their decline:

1. Reliability Issues

Piezo injectors are highly sensitive to high temperatures, which are common in gasoline engines. The extreme heat caused the piezoelectric crystals to degrade over time, leading to a loss of precision and performance. Additionally, their intricate design made them prone to mechanical wear, clogging, and carbon buildup, reducing durability compared to solenoid injectors.

2. High Costs

Piezo injectors are expensive to manufacture due to the high-quality materials required and the complexity of their design. This made them a costly choice for automakers. For consumers, high replacement costs and repairs added to the frustration.

3. Challenges in Gasoline Applications

Unlike diesel engines, which operate at higher fuel pressures and lower temperatures, gasoline engines presented unique challenges that piezo injectors struggled to overcome. High operating temperatures, nozzle shape, and aging piezoelectric crystals all contributed to their failure in many applications.

The Shift Back to Solenoid Injectors

As reliability and cost issues became apparent, automakers started reverting to solenoid injectors. BMW, once a strong advocate of piezo technology, transitioned back to solenoid injectors for newer engines. The BMW N, S, and B engine families now exclusively use solenoid injectors, which are simpler, more reliable, and cost-effective. Other manufacturers followed suit, favoring the proven performance of solenoid systems.

Are Piezo Injectors Completely Gone?

Not entirely. Piezo injectors still have a place in certain diesel engines, where their benefits can be fully realized without the drawbacks that plagued their use in gasoline engines. Diesel engines operate at higher fuel pressures and cooler temperatures, making them better suited to piezo injectors. However, even in diesel applications, some manufacturers are returning to solenoid systems due to cost and longevity concerns.

Lessons from the Piezo Injector Experiment

The journey of piezo injectors highlights the challenges of pushing technological boundaries. While their introduction marked a leap forward in fuel injection precision and performance, their real-world implementation emphasized the importance of practicality and reliability. Advanced technology isn’t always the best choice if it comes at the expense of durability, cost, and ease of service.

The Future of Fuel Injection Systems

Today, most modern engines rely on evolved solenoid injectors, which now offer improved precision, faster response times, and the ability to operate at much higher fuel pressures than earlier models. Combined with advancements in engine management systems, solenoid injectors can match or even surpass the performance of piezo injectors without the associated drawbacks.

So, the next time you pop the hood of a modern car, take a moment to appreciate fuel injectors working tirelessly to keep the engine running smoothly. While piezo injectors may have faded from gasoline engines, their story serves as a reminder of the delicate balance between innovation and practicality in the automotive world.

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