Gasoline Direct Injection, Common Rail Systems

Sky Red Line


An Opel GT with a turbocharged 2.0L engine uses GDI (Gasoline Direct Injection) to develop 260hp. In 2000 Mitsubishi was first to market a turbo GDI engine.

With Franfurt upon us, it would seem time for an update on fuels, engines and emissions research. Many performance automobiles, Porche, BMW, etc., now feature direct injection and, in January at the North American International Auto Show (NAIAS) in Detroit, several automakers introduced1 more gasoline direct injection versions. Yet given the current heat that the globe has been getting, the automotive elite have been switching to an emphasis upon improvements in mileage and emissions.

According to the history recounted in Wikipedia, the first direct injection system was developed by Bosch in 1952. Development waned with the advent of a more cost effective solution provided by the three way catalytic converter. Mitsubishi re-introduced GDI in 1996 and by 2001 had produced over one million GDI engines.

In 2005, Siemens VDO shared an award2 with Robert Bosch GmbH for the development of piezo injection technology. In 2006 GCC3 reported that Bosch was supplying BMW and Mercedes-Benz with gasoline direct injection that uses piezo injectors and by the next year, according to GCC4, Bosch was reporting nearly an 18% Increase in worldwide sales of common-rail systems.

While Bosch has made GDI with solenoid actuation and GDI with piexo-electric actuation, the third generation of the Bosch common-rail system use piezo-inline injectors. The European manufacturers claim piezo injection improves fuel economy and reduces emissions compared to solenoid injection technology.

Stanadyne GDI Pump


A gasoline direct injection supply pump, like the one from Stanadyne Automotive Corp. pictured above, is used in GDI common rail systems in passenger cars. The pump design is lightweight and compact to fit neatly on various engine configurations. It is self-lubricated and contains an internal pressure limiter. Leading companies in direct injection systems include Bosch, Denso, Delphi, Stanadyne, Yanmar and Zexel.

Yet, according to a current Green Car Congress5 post, Delphi has announced production of a gasoline direct injection system that is less expensive than its competition. Gasoline Direct Injection, Common Rail systems require high pressure and precise delivery in very short time frames. Delphi claims that their solenoid actuation can deliver such performance while offering cost benefits over piezoelectric systems.

To distinguish themselves from such significant competition Delphi may be counting upon their work with an advanced variable and two-step valve train that is part of the development by General Motors of newly announced6 HCCI (Homogeneous Charge Compression Ignition) prototype. The GCC article also noted two other Delphi innovations:

1. Stratified Charge
Delphi is developing a GDi system for stratified charge (lean) combustion engines named Multec 20. These systems require very low sulfur fuel to protect lean-burn-compatible catalytic converters, but offer a further fuel economy saving of around 15%. Delphi actuates its outward opening injector for stratified charge systems by a single coil, which offers a significant cost advantage over competitors’ piezoelectric injectors, according to Delphi.

With the same external diameter as the homogeneous charge GDi injector, systems can be fitted to engines with centrally mounted injectors with minimal, if any, revisions to the cylinder head. Due to the injector’s solenoid actuation, the system can use the standard GDi ECU, bringing further simplification and cost savings.

Delphi Multec


Delphi Image

2. Multi-Charge Ignition
To further increase the operating range and improve fuel economy on stratified GDi engines, Delphi has employed its Multi-Charge Ignition System. Multi-Charge features a coil-per-cylinder control system that enables longer spark duration; increased spark energy, and re-ignition in the event of combustion blow-out when liquid is present.

Firing multiple times in a short timeframe, Multi-Charge Ignition ensures initiation of robust combustion and compensation of fuel spray variation due to tolerances in the wet system for example. Additionally, the Multi-Charge system decreases emissions at cold start by ensuring complete combustion of fuel in the cylinder and provides a smoother engine run at critical operating conditions.

A drawback to Stratified Charge Lean Burn is the large amount of NOx being generated; a complex catalytic converter system is required to limit this significant Green House Gas. According to the Wikipedia entry, “lean burn engines do not work well with modern 3-way catalytic converters, which require a balance of pollutants at the exhaust port in order to carry out both oxidation and reduction reactions”. EGR (Exhaust Gas Recirculation) also is used to help reduce high NOx emissions.

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