RESEARCH ANALYSIS: Review of fuel injection systems

Fuel injection systems squirt atomised fuel into the cylinders of an internal combustion engine. They use a series of single- or multi-hole nozzle injectors to spray fuel into the combustion chamber.

Dr Sebastian Schilling, Engineering Director Europe, Gasoline EMS & Powertrain Products, Delphi Powertrain Systems based in Bascharage, Luxembourg, believes regulations that impact powertrain for the foreseeable future are already making an increased penetration of GDI an imperative. "As consumers recognise the benefits of the new generation of boosted gasoline engines, there will be an increased customer pull for these powertrains. Furthermore, as the technology matures and volumes increase, the enhanced value proposition will further improve penetration for downsized, boosted GDI engines when compared with the alternatives."

Since its acquisition of Siemens VDO Automotive in July 2007, Continental has become a major player in fuel injection systems market. Continental's Engine Systems business unit offers electronically controlled injection systems for gasoline and diesel engines. "We see more and more GDI engines in the development phase in Europe with a tendency towards smaller engines, " company executives told just-auto. "Despite some applications with piezo injector and stratified charge, the main trend seems to be stronger downsizing with GDI and turbocharging, for the time being with homogeneous combustion."

Schilling adds that we could see more combinations of turbocharging and direct fuel injection in the next few years. He said: "GDI together with boosting enables gasoline engines to have the low-end torque and driving performance that customers love. When coupled with good NVH [noise, vibration and harshness], the engine's performance should make gasoline engines very competitive with diesels from a customer's perspective."

Although refineries have promised to reduce the sulphur content, until that happens gasoline with a high proportion of sulphur cancels out any fuel savings from using GDI technology. It's more of a political question than a technical one. It is clear, however, that it is technically feasible to reduce sulphur content. We only need to look at Japan where they have already adopted legislation for very low sulphur content in their fuels. It can be done. The question is: at what expense and how quickly?

"The improvement of fuel quality, " said Schilling, "especially the reduction of sulphur in fuel helps all IC-powered powertrains to deliver emission-compliant behaviour far beyond legislative demands. In particular, sulphur-free fuel will support a wider introduction of lean combustion systems with a DeNOx catalyst system even if today the primary trend for smaller engines is moving toward homogeneous and turbo-charging."

Despite the initial forecasts for a booming GDI market, the reality is that the adoption of the technology has been slower. There are a number of reasons for this, most notably the fact that European automakers must commit significant sums to redesign cylinder heads and increase in-house engineering capacity. Going forward, however, just-auto expects to see an increasing adoption of GDI over the next few years. We believe that GDI technology has the potential to outperform the port injection gasoline engine in terms of reducing fuel consumption, increasing engine output, and exhausting cleaner emission.

Meanwhile, direct injection and common rail technology, which injects fuel directly into the combustion chamber at ultra high pressure with electronic control, have boosted diesel's performance. Common rail technology has transformed the diesel engine's noisy and dirty image.

Common rail systems store fuel under high pressure in a rail and use electronic control to achieve accurate injection timing and volume of fuel injection into each cylinder, thereby reducing NOx and particulate matter emissions from diesel engines and lowering noise levels.

Compared with gasoline engines, the diesel engine's main selling points include more than 30% reduced fuel consumption and the fact that it emits about 25% less CO2. Moreover, when the Euro 5 emissions standard takes effect in September 2009, the NOx values for diesel will be roughly 95% lower than when emissions standards were introduced. The same applies to particulate emissions, which have been reduced by 97% over the same period.

Last September, Delphi launched its next generation of diesel fuel injectors, its so-called Delphi Direct Acting Common Rail system. Here, the injector needle is set in motion directly by a piezo ceramic actuator, rather than being moved via an electro-hydraulic circuit as with existing fuel injection technologies. Delphi claims that this enables the injector to spray fuel into the combustion chamber faster and with improved spray momentum and accuracy with faster opening and closing of the needle valve, independent of the injection pressure. The resulting improved combustion control, says Delphi, provides a reduction in emissions, more torque and power across all engine speeds and improved fuel economy and refinement.

With the introduction of the Direct Acting Common Rail, Delphi now offers two families of Diesel common rail systems: the Balanced Valve Fast Servo Solenoid Injector and the Direct Acting Common Rail with the Direct Acting Piezo Injector. Delphi claims that all the key components of both families can be interchanged. As such, one can switch from Fast Solenoid to Direct Acting injector technology without having to make any design change to the base engine. Pump and rail can be kept similar, says Delphi, and, having exactly the same packaging for both injector types, they can be interchanged without any changes to the base cylinder head. The company's Balanced Valve Fast Servo Solenoid Injector family is capable of system pressures up to 2000 bar. It is based on an injector design with balanced servo valve technology. The small size of this actuator allows it to be packaged in-line and in close proximity to the needle providing extremely fast actuation and precise metering.

Meanwhile, Continental is supplying its common rail injection system for the new VW Golf. Volkswagen has converted the entire range of TDIs to 16-valve common rail engines. A spokesperson for VW told us: "Fuel injection for the new Golf's two 1, 968 cc diesel engines is handled by the latest generation common rail system, with up to 1, 800 bar injection pressure and special injection nozzles delivering especially fine atomisation of the fuel. The advantages to the driver are remarkably spontaneous response behaviour and competitive fuel consumption and emissions, when compared to the previous Pumpe Duse engines. The new TDI 16-valve common rail engines also play their part in making the sixth generation Golf the quietest yet, distinguishing themselves with good low-noise properties."

While some auto engineers say that injectors using piezo technology are the only way large diesel engines can meet Euro 5 rules, others say they can improve the performance of conventional solenoid - or electromagnetic - injectors enough to avoid investing in piezo injectors. "The common rail engines fitted to the new Golf, " added the spokesperson, "which meet the Euro 5 regulations, are equipped with the latest generation of piezo in-line injectors. Electrically-controlled piezo crystals, assisted by a hydraulic element, inject the right amount of fuel in just fractions of a second. Compared with conventional solenoid valves, piezo technology enables more flexible injection processes with smaller and more precisely metered fuel volumes. This leads to a very quiet and smooth running engine and exceptionally quick throttle response with low fuel consumption and emissions."

Volkswagen believes that the addition of particulate filters and other after-treatment devices will not make the price premium for diesel too high. "The addition of this technology has not resulted in a prohibitive price premium, with all Volkswagen common rail diesel engines already being fitted with a standard DPF [diesel particulate filter] to reduce particulate emissions to zero."

rather than being moved via an electro-hydraulic circuit as with existing fuel injection technologies. Delphi claims that this enables the injector to spray fuel into the combustion chamber faster and with improved spray momentum and accuracy with faster opening and closing of the needle valve, independent of the injection pressure. The resulting improved combustion control, says Delphi, provides a reduction in emissions, more torque and power across all engine speeds and improved fuel economy and refinement.

With the introduction of the Direct Acting Common Rail, Delphi now offers two families of Diesel common rail systems: the Balanced Valve Fast Servo Solenoid Injector and the Direct Acting Common Rail with the Direct Acting Piezo Injector. Delphi claims that all the key components of both families can be interchanged. As such, one can switch from Fast Solenoid to Direct Acting injector technology without having to make any design change to the base engine. Pump and rail can be kept similar, says Delphi, and, having exactly the same packaging for both injector types, they can be interchanged without any changes to the base cylinder head. The company's Balanced Valve Fast Servo Solenoid Injector family is capable of system pressures up to 2000 bar. It is based on an injector design with balanced servo valve technology. The small size of this actuator allows it to be packaged in-line and in close proximity to the needle providing extremely fast actuation and precise metering.

Meanwhile, Continental is supplying its common rail injection system for the new VW Golf. Volkswagen has converted the entire range of TDIs to 16-valve common rail engines. A spokesperson for VW told us: "Fuel injection for the new Golf's two 1, 968 cc diesel engines is handled by the latest generation common rail system, with up to 1, 800 bar injection pressure and special injection nozzles delivering especially fine atomisation of the fuel. The advantages to the driver are remarkably spontaneous response behaviour and competitive fuel consumption and emissions, when compared to the previous Pumpe Duse engines. The new TDI 16-valve common rail engines also play their part in making the sixth generation Golf the quietest yet, distinguishing themselves with good low-noise properties."

While some auto engineers say that injectors using piezo technology are the only way large diesel engines can meet Euro 5 rules, others say they can improve the performance of conventional solenoid - or electromagnetic - injectors enough to avoid investing in piezo injectors. "The common rail engines fitted to the new Golf, " added the spokesperson, "which meet the Euro 5 regulations, are equipped with the latest generation of piezo in-line injectors. Electrically-controlled piezo crystals, assisted by a hydraulic element, inject the right amount of fuel in just fractions of a second. Compared with conventional solenoid valves, piezo technology enables more flexible injection processes with smaller and more precisely metered fuel volumes. This leads to a very quiet and smooth running engine and exceptionally quick throttle response with low fuel consumption and emissions."

Volkswagen believes that the addition of particulate filters and other after-treatment devices will not make the price premium for diesel too high. "The addition of this technology has not resulted in a prohibitive price premium, with all Volkswagen common rail diesel engines already being fitted with a standard DPF [diesel particulate filter] to reduce particulate emissions to zero."

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