GDi-(Gasoline Direct Injection)
Published: 28 June 2019
350 bar GDi: Your best solution to rising regulations.
Gasoline direct injection (GDi) engines have certainly earned their rightful place on advancing propulsion roadmaps. The technologies behind these systems deliver a path to increased performance, improved fuel economy and reduced carbon dioxide (CO2) emissions through more precise, leaner and complete combustion.
Granted, the benefits do have a few strings attached. GDi systems are generally more complex to engineer, manufacture and maintain. Durability also comes into play given the high pressures and extreme heat fuel lines and injectors, for instance, need to withstand. Unnecessary service visits and owner complaints can erupt when normal-operation noise from the fuel pump is interpreted as a problem. And then there’s increase in particulate emissions – both in mass (PM) and number (PN) – due to reduced evaporation and mixing time the fuel has when injected directly into the combustion chamber before it is ignited.
With gasoline direct injection, the question becomes: How do you maximise the positives and minimise the negatives?
One way is through pressure. Most GDi systems on the market today operate at 200 bar or lower pressures. Engineers have tinkered with moving past 200 bar in an attempt to abate and even eradicate these tradeoffs.
The premise: The higher the pressure, the smaller the fuel droplet size. The smaller the droplet size, the more efficient the evaporation. The more efficient the evaporation, the lower PM/PN.
The problem: When you increase pressure, you intensify durability demands. You tax fuel economy gains for the needed boost in engine torque. And you trigger louder, irritating pump noises through higher loads.
As a result, nobody has been able to make 200-plus bar pressure gasoline direct injection systems work – and work seamlessly – without compromises.
Delphi Technologies 350 bar GDi system for low particulate emissions.
With the introduction of our leading-edge 350 bar gasoline direct injection system, Delphi Technologies is the first in the industry to push the pressures and forego the flaws. This latest propulsion innovation delivers:
- Substantially reduced particulate emissions. The system produces 70 percent smaller particles than current systems, allowing you to hit Euro 6d and China 6 emissions standards with simpler after-treatment systems.
- Advanced componentry built for speed and endurance. The system features redesigned elements – such as the Multec 14 fuel injectors– that are faster and more durable than the competition at these higher pressures.
Improved performance. The higher pressures boost coking resistance, trimming the build-up of cooked fuel deposits that can foul the injectors – and reduce customer satisfaction scores.
Lower fuel-pump noise thresholds. The newly designed GFP2 gasoline fuel pump operates at lower dBA (decibels) achieving industry-leading noise levels.
The system also boasts upgrades in materials, as well as new component fabrication and system manufacturing techniques that reduce complexity and stabilize costs. Finally, the new 350 bar GDi system has been developed and tested for all international fuel blends, allowing you to easily – and quickly – deploy in all global gasoline powertrain platforms.
Fast Take: 350-bar GDi – The pressure of choice
How Delphi made it work.
In developing the new 350 bar gasoline direct injection system, Delphi Technologies engineers encountered – and resolved – several crucial challenges.
The first was particulates. They had to engineer a system that would reduce fuel droplet size, plus increase spray timing and speed to remove the conditions that allow particulates to form.
The second was wear and tear. They knew higher pressures put increased stress on fuel injection components. As a result, fuel rail, injector and pump stability and longevity, to name a few, had to be improved.
The third was fuel economy. The energy needed to create higher bar pressures is derived from the engine. The system had to be designed to produce more power with minimal increases in torque to avoid hits to fuel economy. The same was true for durability. Making the system stronger could not equate into making it bigger or heavier. The design had to be small, compact and flexible; otherwise they’d see offsets in fuel consumption.
Finally, they had to watch that noise. With higher pressures you get higher loads – particularly in the fuel pump. Delphi Technology’s Gen I fuel pump was already best-in-case on exterior noise. The engineers were determined to sustain this level of performance.
Over the course of about 18 months, the engineers overcame all of these challenges, reinventing the 200 bar system largely through the development of new software and closed-loop controls, changes in prototype development and testing approaches, as well as fuel injector and pump advances.
With the new Multec 14 (M14) fuel injector, the team designed it to operate at higher pressures, and provide faster opening and closing times. Faster operation was achieved by reducing the internal friction of the valve and the overall mass of the moving components. Other key enhancements included:
- Reducing number of welds to improve durability.
- Redesigning the injector seat to simplify manufacturing, improve corrosion resistance and enhance structural integrity.
- Improving mounting methods to better withstand higher pressures and minimise injector-to-cylinder head misalignments.
- Optimising magnetic circuits to better trigger and manage injector events.
- Improving fuel flow efficiency by reducing internal friction and redesigning the armature assembly.
For the new GFP2 fuel pump it was all about delivering better durability and steady performance, under higher pressures without increasing the noise levels. This was achieved by:
- Specially developed seals at the plunger/bearing interface designed to minimise internal fuel loss. This boosts pressure at very low RPMs, delivering faster engine starts, as well as 40 percent overall better efficiency than competitors' pumps.
- Making changes to pressure- and load-bearing elements, including the spill valve, by removing welds and using stronger materials in order to improve overall durability.
- Implementing performance enhancements, including redesigning – and in some cases eliminating – several internal elements, such as O-rings on the damper cup assembly, which can be prone to leaks and contribute to evaporative emissions.
- Deploying packaging upgrades, including a 360-degree flange and a 180-degree electrical connector, to allow the pump to fit virtually any engine design.
- Developing improvements for the fuel inlet, internal damper assembly, mounting flange and outlet fitting to reduce noise levels.