Delphi Technologies Next Generation GDi-System improved ......corresponding 400 bar capable high...

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- 1 - Dr. techn. Walter F. Piock, Dr.-Ing. Guy Hoffmann, Joseph G. Spakowski M.Sc., Dr. Gavin Dober, Dipl.-Ing. Baudouin Gomot, Dr. rer.nat. Holger Hülser Delphi Technologies, Bascharage Luxembourg Delphi Technologies Next Generation GDi-System improved Emissions and Efficiency with higher Pressure Das neue GDi-System von Delphi Technologies verbesserte Emissionen und Effizienz mit höherem Druck Abstract In 2016 Delphi Technologies successfully started production of the world’s first 350 bar GDi - System enabling its customers to address their demand for higher performance, lower fuel consumption and lower engine emissions, especially particulate emissions. However, further benefits are achievable beyond 350 bar. Advanced combustion work has demonstrated the potential of increased fuel pressure to further reduce emissions and improve fuel consumption due to better atomization and higher combustion efficiency. These positive results triggered an evolutionary component development of a next generation GDi-System which is capable of fuel pressures up to 600 bar. The developed injector required structural modifications of the high pressure vessel, but optimization of the magnetic path has allowed retaining the same drive energy levels as today’s 350 bar injectors and has allowed maintaining the current packaging envelope. The high pressure pump carries over the 350 bar concept of an outlet metered single piston pump, but requires adaption of some of the critical components and interfaces for the significantly higher loads. The demand for higher pressures at low engine speeds has also led to the introduction of a new internal pump feature which boosts pump efficiency and consequently brake engine efficiency. Complementary to the advances on the wet components, the control system has been developed with a focus on improved injection accuracy over lifetime. Engine results compare the key performance characteristics, fuel consumption and emissions, against a state of the art 350 bar injection system. This new technology offers an opportunity to make gasoline engines more efficient and significantly cleaner. Introduction For several years the global automotive industry has been in a fundamental transformation process from conventional internal combustion engine powered vehicles towards electrified vehicles, including hybridized and even full electrical powertrains. This trend is driven by increasingly strict global emission standards and planned driving bans for cities or regions in a first step for light vehicles with Diesel engines and at a later step for all combustion engines. The recently agreed climate objective to keep the global warming temperature rise below 2°C until the end of this century [1] requires significant contributions from the transportation sector to further reduce greenhouse gases emissions. The proposed and currently discussed CO2 targets from the European Commission for 2030 and beyond are forcing the

Transcript of Delphi Technologies Next Generation GDi-System improved ......corresponding 400 bar capable high...

Page 1: Delphi Technologies Next Generation GDi-System improved ......corresponding 400 bar capable high pressure pump (GFP2.35) for a 4-cylinder 350 bar application [6]. Figure 3: Gasoline

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Dr. techn. Walter F. Piock, Dr.-Ing. Guy Hoffmann, Joseph G. Spakowski M.Sc., Dr. Gavin Dober, Dipl.-Ing. Baudouin Gomot, Dr. rer.nat. Holger Hülser

Delphi Technologies, Bascharage Luxembourg

Delphi Technologies Next Generation GDi-System – improved Emissions and Efficiency with higher Pressure

Das neue GDi-System von Delphi Technologies – verbesserte

Emissionen und Effizienz mit höherem Druck

Abstract

In 2016 Delphi Technologies successfully started production of the world’s first 350 bar GDi-System enabling its customers to address their demand for higher performance, lower fuel consumption and lower engine emissions, especially particulate emissions. However, further benefits are achievable beyond 350 bar. Advanced combustion work has demonstrated the potential of increased fuel pressure to further reduce emissions and improve fuel consumption due to better atomization and higher combustion efficiency. These positive results triggered an evolutionary component development of a next generation GDi-System which is capable of fuel pressures up to 600 bar. The developed injector required structural modifications of the high pressure vessel, but optimization of the magnetic path has allowed retaining the same drive energy levels as today’s 350 bar injectors and has allowed maintaining the current packaging envelope. The high pressure pump carries over the 350 bar concept of an outlet metered single piston pump, but requires adaption of some of the critical components and interfaces for the significantly higher loads. The demand for higher pressures at low engine speeds has also led to the introduction of a new internal pump feature which boosts pump efficiency and consequently brake engine efficiency. Complementary to the advances on the wet components, the control system has been developed with a focus on improved injection accuracy over lifetime. Engine results compare the key performance characteristics, fuel consumption and emissions, against a state of the art 350 bar injection system. This new technology offers an opportunity to make gasoline engines more efficient and significantly cleaner.

Introduction

For several years the global automotive industry has been in a fundamental transformation process from conventional internal combustion engine powered vehicles towards electrified vehicles, including hybridized and even full electrical powertrains. This trend is driven by increasingly strict global emission standards and planned driving bans for cities or regions in a first step for light vehicles with Diesel engines and at a later step for all combustion engines. The recently agreed climate objective to keep the global warming temperature rise below 2°C until the end of this century [1] requires significant contributions from the transportation sector to further reduce greenhouse gases emissions. The proposed and currently discussed CO2 targets from the European Commission for 2030 and beyond are forcing the

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introduction of zero- and low-emission vehicles. For zero-emission vehicles like battery electric vehicles (BEV) or fuel cell (FC) vehicles, a CO2 neutral generation infrastructure for electricity and hydrogen must still be established in order to reduce overall greenhouse gas emissions. The low-emission vehicles are powered by hybrid (mild hybrid electric vehicle (MHEV) and hybrid electric vehicle (HEV)) and plug-in hybrid (plug-in hybrid electric vehicle (PHEV)) powertrains, equipped with a conventional engine and an electric machine. In this challenging environment, the internal combustion engine will remain the dominant propulsion source on a global level beyond the end of the next decade although electrification will make most of the contribution to reduced emissions. A potential scenario is shown in Figure 1. Especially in markets and regions with increasingly stringent local pollutant and CO2 emissions regulations the powertrain mix will be even more biased towards zero- and low-emission technologies. Although the predictions are frequently changing based on sales numbers and announcements, the majority of the most recent studies show that 85% of the globally produced vehicles in 2030 will still be powered by an internal combustion engine and up to 15% will be zero-emission vehicles.

Figure 1: Propulsion trend for passenger cars and Light Vehicles

Although a potential termination date for the development, production and sales of internal combustion engines is in discussion or has already been announced [2], a significant number of improvement activities for combustion engines are still required in order to support the global mobility demand while fulfilling the legal requirements. Furthermore, alternative fuels from renewable sources like bio-fuels or e-fuels may delay the complete exit of the established, well proven, combustion engine technology for some application areas and markets. In the period considered up to 2030 the number of Diesel powered vehicles will certainly decrease but not disappear from the light vehicle market. The majority of this reduction will be compensated by gasoline engines with conventional stoichiometric operation allowing the usage of simple three-way catalyst technology and where required gasoline particulate filter, both operating with very high effectiveness. The lower fuel efficiency of gasoline engines requires very focused improvements on the combustion and engine technology side to partially compensate for the significantly reduced contribution of Diesel powered vehicles to meet the regulatory defined fleet average consumption. Even for hybrid powertrains a high level of engine technology content adds to the overall efficiency and is required for an efficient hybrid propulsion system [3].

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The majority of the gasoline engine technologies and sub-systems introduced or under development focus on the delivery of more performance, lower emissions and better fuel consumption. Among those the fuel injection system is one key technology building block for more efficient and cleaner combustion. The injection of gasoline directly into the combustion chamber enables the highest degree of spatial and temporal flexibility for the fuel introduction. An additional control parameter is the fuel pressure of the injected gasoline. Figure 2 shows on the left hand side the impact of fuel pressure on spray atomization from a gasoline direct injection nozzle characterized by the Sauter Mean Diameter (SMD) and the droplet diameter representing large droplets (Dv90 – the droplet diameter below which 90% of the total liquid volume is occupied by smaller droplets). The increasing injection pressure is very effectively utilized to generate smaller droplets and higher pressure shows a continuous improvement of atomization. On the right hand side the effect of fuel pressure on particulate number emissions from a homogenous stoichiometric combustion engine is shown. With increasing injection pressure of the given gasoline direct injection nozzle (here with counterbores downstream of the flowholes) the number of particulates in the exhaust gas is significantly reduced across all particle size classes.

Figure 2: Fuel pressure impact on atomization and particulate emissions

Mixture formation is enhanced by the improved atomization and higher spray momentum, which leads to cleaner combustion with lower engine-out gaseous emissions. In addition, the higher fuel pressure helps to remove injector tip deposits to reduce or even prevent diffusion flame effects at the injector tip [4]. The new homologation cycles (e.g. WLTC) and the need to be compliant to real world driving (RDE) are extremely challenging targets driving combustion and calibration development for both steady state and dynamic operation in all environmental conditions. Thus, even for system configurations implementing a gasoline particulate filter, a higher fuel pressure is a very powerful parameter to improve engine-out performance almost irrespective of the condition, and is therefore one of the key development areas of fuel system suppliers [5]. Since 1996 when the first gasoline engines with direct injection were introduced in the Japanese market the fuel pressure levels have been elevated in steps, mainly triggered by emission legislation changes, Figure 3. At the end of 2016, Delphi Technologies introduced

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globally the first 400 bar capable large volume production injector (Multec 14) and the corresponding 400 bar capable high pressure pump (GFP2.35) for a 4-cylinder 350 bar application [6].

Figure 3: Gasoline Direct Injection - Fuel Pressure Trend

The increasing emission and efficiency challenges for gasoline engines are requesting a further improved fuel injection system capable of 500 bar fuel pressure or even beyond. Delphi Technologies has addressed this future market demand with the development of a new generation GDi fuel system which will be presented in the chapters below.

Multi-Hole Injector - Multec 16

Triggered by the opportunity to substantially improve particulate emissions and coking drift performance associated with higher pressures, Delphi Technologies has gradually increased the injection system pressure capability in each new injector generation, see Figure 4. In terms of mixture formation, the higher pressure approach shows a significantly higher effectiveness in improving mixture preparation compared to practical fuel heating concepts [7] and was the selected development direction for the next generation gasoline direct injection systems. In addition to the pressure capability increase, continuous improvements on critical injection performance and durability parameters were implemented and the associated fueling correction functions were further improved in order to meet more stringent requirements especially for small injected quantities. Based on the current mainstream Multec 14 (M14) with up to 400 bar system pressure capability, the next generation Multec 16 (M16) will introduce a substantially increased pressure capability to 600 bar, while remaining compatible with the current production line and packaging. The injector pressure vessel as well as the injector-to-rail interface are based on the Multec 14 solutions with detailed optimizations in order to comply with the increased pressure requirements. The injector tip diameter is currently proposed at 6 mm. Meeting increased magnetic force requirements and achieving high pressure fueling performance within the given package outline and under increased mechanical strength constraints required more substantial design changes in the central actuator portion of the injector. Nevertheless the

Multec 14

GFP2.35

Delphi Technologies

Next Generation

GDi-System

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newly developed Multec 16 injector shows increased fueling performance across the whole pressure range up to 600 bar while being fully optimized for the requirements of the next generation closed loop correction functions. The increased system pressure range can be used to achieve faster injection rates, giving more time for fuel-gas mixing and evaporation and an increased dynamic range using pressure modulation to further significantly optimize particulate emissions.

Figure 4: Delphi Technologies - GDi Injector Design Evolution

In Figure 5 an example for the flow curve behavior is shown at 350 and 600 bar fuel system pressure. The development target was to optimize the flow curve shape in terms of ballistic slope and low end linearity while meeting the requirements for increased maximum operating pressure and larger static flow rates. The achieved shot-to-shot flow variation at 600 bar meets the same tight requirements as the 350 bar base injector. In terms of drive energy the new actuator design of the Multec 16 was able to reduce substantially the ECU driver requirements at 350 bar and achieve 600 bar without the necessity to increase driver requirements above the current 350 bar baseline [8].

Figure 5: GDi Injector Multec 16 – Flow Performance and Drive Energy Demand In Figure 6 the multi-pulse behavior of the new generation Multec 16 is shown at 25°C ambient conditions. Simulation results in the left hand graph show the variation of the inter-

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pulse dwell time between pulse width 1 and 2 for a range of pulse width 1 between 0.4 and 1 ms and a constant pulse width 2 of 1 ms. Results show a slight increase of the injected mass in the second pulse as the dwell time is reduced. This effect is mainly due to a faster opening of the second pulse due to the residual magnetization of the first pulse. The lower limit of the inter-pulse delay is defined by the travel time of the pintle-armature assembly while fueling and the travel time of the decoupled armature when the injector is closed. At the lowest dwell time limit the injector is not closing completely in-between the two pulses. The right graph shows results for the variation of dwell time for a range of pulse width 2 between 0.4 and 1 ms and a constant pulse width 1 of 0.5 ms. Results show the largest percent increase for the smallest second pulse length at a dwell time where the internal armature movement between pulses retains a maximum of kinetic energy for the opening in the second pulse. Multi-pulse behavior at 100°C is comparable to the behavior at ambient conditions. Due to a reduced viscosity at elevated temperatures the injector dynamics slightly amplify the increase in second pulse fueling without negatively affecting the short dwell time capability. The level of multi-pulse performance of the Multec 16 safely meets the development target of 0.5 ms minimum dwell time.

Figure 6: GDi Injector Multec 16 – Multi-pulse Performance at Variable Dwell Time and Ambient Temperature

One of the key focus areas for the injector development is the further reduction of particulate emissions and the optimization of the long term emission stability. In Figure 7 the smoke drift behavior is analyzed across a system pressure range between 100 and 600 bar. In each test the smoke drift from an initially clean injector nozzle is recorded after a standard 10 hour coking cycle. The overall trend of a decreased PN drift with an increased system pressure is clearly displayed. In addition, an optimization of the nozzle geometry shows the ability to improve particulate emissions at every pressure level. The effect of the injection pressure on particle emissions is due to better atomization and mixture formation in the combustion chamber but also due to reduced diffusion combustion at the injector tip. The higher pressure causes a stronger expansion of the spray jet emerging from the nozzle hole, which in turn leads to a more effective shear cleaning of deposits from the counterbores (Figure 7, bottom left). Deposit formation on the end face of the injector is then also suppressed. Through the combination of nozzle geometry optimization based on CFD and physical testing, the increase of manufacturing capabilities in industrializing complex nozzle

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geometries and the increase of the system pressure to 500 bar and above an optimal injector solution can be proposed for a broad range of flow requirements and injection strategies.

Figure 7: GDi Injector Multec 16 – Seat Nozzle Parameters and Coking Drift Performance In addition to the increased cleaning performance and robustness against deposits at high pressure, engine performance can also benefit from the improved spray penetration and mixing behavior. As shown in Figure 8, there is a substantial reduction of injection time for the same fuel quantity achieved when increasing system pressure.

Figure 8: GDi Injector Multec 16 – Fuel Pressure and Spray Characteristics The end of injection spray penetration for the same quantity is very similar across the pressure range. While Figure 2 shows the effect on droplet size and atomization of a pressure increase, in Figure 8 the increase in the overall spray angle is clearly visible when testing the same nozzle at 100, 350 and 600 bar. The green curves represent behavior for an injected mass of 10 mg, while the blue curves are for an injected mass of 5 mg. The

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increase in overall spray angle is visible in each individual flow hole and can be explained by the increased atomization energy available at high pressure as well as an increase in cavitation effects accelerating the primary breakup [9]. Through proper nozzle geometry optimization the best compromise can be achieved between the required spray momentum and angle to optimize air-fuel mixing and to reduce the spray penetration to avoid cylinder and piston wetting.

High Pressure Pump - GFP3

The current Delphi Technologies high pressure GDi pump (generation 2 – GFP2) is in production since 2016 and has been validated for pressures up to 400 bar. It is a high value, single-piston camshaft driven pump which delivers continuous fuel rail operating pressures up to the maximum pressure. It includes an integrated flow control valve for accurate control of fuel demand and an integrated overpressure relief valve. The pump is currently in production with 8, 9 and 10 mm plunger diameters and covers a large range of fuel flows. The increase of the fuel pressure requires some conceptual considerations on the base engine as well on the pump component level to address the mechanical and functional challenges, Figure 9. In most of today’s gasoline engine applications the single piston pump is operated by the specific cams of the engine camshaft which convert the cam torque via a roller lifter to an axial force. This axial load is a function of the generated fuel pressure, illustrated on the upper left hand diagram in Figure 9. The higher fuel pressure and the resulting higher pump load is causing higher peak torques as well as more pronounced cam torque oscillations which may negatively impact the camshaft drive and the cam-phaser function. The higher loads have brought about larger packaging sizes required for the newly designed roller lifters. Roller lifters have had to increase the diameter of the roller itself (typically from 16 mm or 18 mm to 20mm diameter) and allow use of higher load bearings. The contact floor of the roller lifter that mates with the plunger tip has also had to be crowned to make sure that the contact interface under load does not reach the outer diameter edges of the plunger and keep the Hertzian contact stress at a safe level for durability. All these changes increase the packaging height of the roller lifter, the diameter as well as the mass of the moving parts, which then requires a higher load plunger return spring which will also add to the load and torque increase. The cam that drives the roller lifter and pump plunger requires a larger base circle radius to keep the cam stresses in a safe zone for durability. This also increases the packaging size required in the engine. Some high flow applications with larger plunger sizes may require a spring with an increased load in excess of 1000 N to prevent separation of the roller lifter and cam. For the pumping function itself the higher pumping pressure is causing an efficiency reduction, shown in the lower left hand graph in Figure 9. Considering the full pressure range of gasoline during the pumping event from feed pressures around 5 bar up to system pressure the compressibility of the liquid fluid plays a non-neglectable role. This physical behavior cannot be influenced but the overall impact on the pump level can be reduced by optimization of the pumping chamber volume (dead volume). The dead volume of the GFP3 pump is optimized to maintain high pumping efficiency and low pressure pulsation generation. The second key efficiency impact is caused by the internal by-pass flow between

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pump plunger and sleeve. The higher the pressure and the lower the pumping frequency the more fuel is escaping during the pumping stroke from the pressure chamber into the low pressure region. Reducing this internal leakage helps significantly to boost the typical low speed efficiency of the pump.

Figure 9: High pressure pump challenges and new Delphi Technologies GFP3 high

pressure pump

The new generation high pressure pump GFP3 is derived as an evolutionary development from today’s GFP2 addressing both the mechanical and functional challenges arising with the higher fuel pressure demand. The new GFP3 pump design incorporates all of the key low noise features and durability / quality lessons learned on the GFP2 pump but has some critical enhancements to achieve continuous operation at 600 bar with high efficiency at low rpm. The GFP3 pump includes a forged body with integral flange, a tamper proof threaded-in outlet fitting, an inlet valve assembly that is threaded-in, a Pressure Relief Valve (PRV) that requires no external fuel sealing plug. A new design feature of the pump is a Plunger Ring Seal (PRS) for high volumetric efficiency operation. The forged body with integral flange allows for stronger interfaces between components and reduced use of laser welds which can cause contamination and distortion of the final assembly. In the GFP3 forged body pump, no press fit joints or laser weld joints are exposed to high pressure fuel. The integral flange permits near perfect perpendicularity between the plunger bore axis and the flange mounting surface, thus offering an inherent reduction in side load of the plunger which is a critical parameter especially with increased axial forces. A threaded-in outlet fitting is enabled by the forged body. The body contains a hub for the outlet fitting threaded port and enables a region for a final tamper proof and fuel sealing weld. The pressure load is handled by the threaded fit between the fitting and body. The high pressure seal is made by a metal to metal seal achieved with a special geometry on the face of the fitting and the mating surface in the body. The design contains a low pressure bleed off path back to the low pressure circuit within the pump in case the high pressure seal has a leak. The threads and tamper proof laser weld are only exposed to low pressure fuel. The GFP3 pump uses the very robust and low noise inlet metering valve from the GFP2 pump but it is housed in a new carrier component that also has a threaded interface inside the body. This allows no internal welds and completely supports the higher pressure. The PRV for the GFP3 pump has been redesigned to handle the higher pressures and also has

Pump modifications for High Pressure

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inlet valve –no internal weld

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69 [mm] plunger

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Mechanical Challenge

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a new orientation inside the pump. The new orientation allows the PRV to be leak tested during the assembly process and does not require an external port/plug that has to seal fuel. The PRV is still pressure balanced like the GFP2 pump. The GFP3 pump also has improved noise performance. The pump includes the key low noise features from the GFP2 pump but is enhanced by the stiffness of the forged body, improved low pressure circuit structure and a geometric design to mitigate noise. The GFP3 pump also includes the new Delphi Technologies high efficiency Plunger Ring Seal (PRS). The PRS is a polymer seal that is assembled to the plunger and moves dynamically within the bore of the sleeve (Figure 10, left image). The seal is designed to minimize the internal leakage between the plunger and sleeve. As stated previously, this internal leak flow is more important at lower engine speeds. The PRS pump achieves >40% improvement in pumping efficiency at engine cranking speeds (250 camshaft rpm and lower) at 500 bar system pressure compared to leading current production GDi pumps (Figure 10, middle plot). This increase in pumping efficiency at low rpm allows the desired rail pressure for engine starting to be reached much faster (fewer pump strokes) which enables much faster engine starts, (Figure 10, right plot).

Figure 10: GFP3 – Sealing concept, volumetric efficiency and pressure build-up

Since GDi system pressure rise and high fuel delivery requirements at low rpm often dictate pump plunger diameter size and cam sizing, this new PRS pump, in most applications will allow the plunger diameter to be downsized [10]. The advantage of downsizing is a reduction in cam loading, which leads to lower cam stresses and drive torque, and enables the implementation of higher fuel pressure systems without significant changes to existing pump drive architecture (roller lifter and cam). Simply reducing the clearance to improve efficiency is not a robust solution considering the aggressive and low lubricity of global gasoline fuels and the potentially increased side loads due to higher pressures. The introduction of the continuous polymer seal increases the friction between plunger and sleeve and leads to higher mechanical losses when the plunger is moving. The benefit of using the seal is to minimize or practically prevent the internal leakage of already compressed fuel from the pumping chamber into the low pressure circuit. Since the pump spill valve must close earlier in a pump without the seal, as shown in the left graph of Figure 11, the plunger experiences a force due to pressure for a longer duration resulting in more work required to pump the fuel. When considering the overall pump efficiency, this effect of the pump without a seal is offset by the increased friction of the pump with a seal.

Product Feature Fast Pressure Build up High Volumetric Efficiency

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The right graph of Figure 11 presents the mechanical power required to drive the pump at 1000 pump rpm for various pressures and fuel delivery values. The camshaft power requirement consists of 1) a nearly constant mechanical friction portion of about 250 W seen on the vertical axis at the zero flow and 2) a variable part from the compression work which shows a nearly linear behavior over the volumetric flow range at constant pressures. At the investigated camshaft speed of 1000 rpm the measured mechanical power at 100 bar fluid pressure confirms a small mechanical efficiency disadvantage of up to 5% at same delivered volume when using the seal. At 350 bar fluid pressure, the losses due to seal friction offset its efficiency advantage, while for 500 bar the estimated advantage of the pump with PRS seal can be very significant.

Figure 11: Pumping power comparison at constant speed and variable fluid delivery

The experimental test data for pump drive torque can be used to model the energy consumption of the pump over a typical driving cycle for a typical midsize vehicle. The result is shown in Figure 12 for three pump and system pressure configurations. At lower speeds and for smaller fuel mass demands, the advantage of the pump with seal at high pressures is increasing due to its insignificant hydraulic losses and correspondingly lower torques. As the WLTC cycle has a large amount of low speed driving the impact on the total pump energy consumption over the cycle can be very large. Despite the higher power requirement to drive a pump having a PRS due to increased friction, with the PRS a substantial improvement in pump drive energy at 600 bar is predicted.

Figure 12: Simulated System Hydraulic Energy Demand in WLTC (World harmonized Light

duty Test Cycle)

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The observed pump performance characteristic especially at higher pressures makes this design very attractive for engine applications with fuel pressures of 350 bar and above. For automotive applications, long-term reliability is a key requirement for any component or system. Extensive testing was conducted to validate the robustness of the PRS pump and to see how the seal would fare over an extended life cycle. Several 1000 hour and 3000 hour tests were designed with multiple engine rpm stages to simulate engine operation and were performed with pumps that included varying groove and seal dimensions and also plunger to sleeve clearances. None of these results showed any degraded performance at the end of test. The left plot in Figure 13 shows example results from a 3000 hour durability test. Results in this plot show the pump volumetric efficiency vs. several pump cam rpms for different intervals of test completion. The test results also showed there was no physical degradation of the sealing or the inside bearing surface of the Sleeve. The pictures on the right in Figure 13 show the seal sealing surface at 0 hour and also after the test completed at 3000 hours. The top picture shows the inside diameter bearing surface of the piston sleeve.

Figure 13: High Efficiency Pump – Durability Performance

Several other validation runs with different plunger sizes from 8 to 10 mm, different fuels and pressures up to 600 bar were performed and confirm the required long term stability of the PRS. Complementary pumps are also accumulating mileage in fleet cars with no functional degradation which further demonstrates the suitability of the concept for gasoline pump applications. As already mentioned above, the excellent volumetric efficiency at low engine rpms may allow the usage of a smaller piston diameter for a given application. Therefore pumps with 7 mm and smaller plunger diameters are being prepared for further validation and customer testing. This plunger downsizing together with an increased cam lift could potentially allow an easy drop-in replacement when a higher fuel system pressure is foreseen for the next engine upgrade.

High Pressure Rail For increasing fuel rail pressures, brazed rail technology is approaching a structural limitation. With fuel pressures above 500 bar the conduit wall thickness requires more than 5 mm which makes it challenging for the cross hole machining and deburring as well as for

Piston Sleeve 3000 [h] EOT

gliding

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gliding

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8 [mm] plunger diameter, 4.25 [mm] cam lift – E10

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the consistent brazing fill of the interface between the injector socket and conduit. At Delphi Technologies the forged fuel rail technology and machining is well established for Diesel applications up to 3000 bar and is as applicable and available for stainless steel gasoline fuel rails. In Diesel applications the injector is typically connected via a separate high pressure pipe to the remotely located high pressure rail, while on gasoline engines the much lower fuel pressure allows the usage of a relative simple O-ring sealing interface between the injector and rail. For an increased pressure level three different connection and sealing concepts are available for customer applications. The first is a similar concept as for Diesel engines with a remote fuel rail linked via individual threaded high pressure tubes to the injectors. The second one is also a metal to metal connection where the injectors are directly clamped to the fuel rail. The best value and preferred solution is a further refined O-ring sealing interface which allows a carry-over injector packaging for the relevant cylinder head environment. Cold sealing performance as well as pressure cycling validation confirm the capability of this design under typical tolerance conditions for cylinder head and fuel rail. In view of the complexity, weight and cost of the fuel rail, the overhead fuel rail design offers significant advantages over a fuel rail with an off-set conduit and typical cross-drillings and plugs and is therefore highly recommended for higher fuel pressure applications. In Figure 14 the fuel rail mass comparison of different fuel rail architectures is illustrated. The higher stresses caused by the increased fuel pressure require a greater wall thickness of the load carrying portions of the component, as well as a careful deburring process at the hole intersections where fatigue stresses are critical. For weight sensitive applications an autofrettage process can be applied during the fuel rail manufacturing. Inner portions of the fuel rail will be exposed to a very high pressure and yield plastically during this process step leading to a higher fatigue resistance. This allows smaller wall thickness and a remarkable weight reduction of up to 25% compared to a standard fuel rail.

Figure 14: Gasoline fuel rail technology for high pressure

In many applications the injector is clamped to the cylinder head and axially loaded by the injector spring clip and fuel pressure. The additional hydraulic force from the elevated fuel pressure needs to be considered at the injector head adapter and interface to the cylinder head as well as at the mounting concept for the fuel rail on the engine.

350 [bar] 600 [bar]

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forged rail

Autofrettage

forged rail

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appr.

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auto

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as

s

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Engine Control System

Increasing the rail pressure requires improvements in the engine control system, especially with respect to injector control. Thus, Delphi Technologies has adapted the GCM7 engine controllers to the new demands, as shown in Figure 15.

Figure 15: Control system for next generation GDi engine

With higher fuel pressures, the injection pulse duration decreases for a given fuel mass. Thus, an even higher accuracy of the injector control and monitoring is required, especially in the low fuel mass “ballistic” range with partial pintle lift and the transition zone to high fuel masses with linear dependency of fuel mass on pulse width. Accurate control of the fuel delivery becomes even more important as the trend towards a higher number of small injection pulses per stroke continues for efficient cold start emission reduction. Delphi Technologies’ custom DIFlex ASIC provides a flexible solution to precisely control the current for not only GDi injectors with up to 5 injections at pressures up to 600 bar, but also injectors for CNG or water. To account for individual small deviations between the injectors and ageing effects, the injected fuel quantity needs to be monitored and corrected for each injection and each injector individually. Delphi Technologies’ Injector Closed Loop Control (ICLC) function, detecting injector opening and closing from the injector low side voltage trace has proven to be a very efficient method for that purpose [5]. High-resolution sampling of this injector feedback voltage in time and amplitude is key to determine the injector opening and closing precisely. The C3MIO highly integrated systems chip provides sufficient resolution even for the increased requirements with 600 bar. As the GCM7 ECU family can be equipped with up to 6 CPU cores with up to 300 MHz clock frequency, sufficient computing power is available for the control function upgrades required not only for ICLC improvements for 600 bar but also for further developments beyond Euro 6d.

O

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S

C3PS ProcessorLockstep2+ Core10 MB Flash

DIFlex

LinearO2Flex

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AFR Sensors

Up to 6 CPU cores for high-speed processing of

injector closed-loop control

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CORE CORE CORE

CORE CORE CORE

Page 15: Delphi Technologies Next Generation GDi-System improved ......corresponding 400 bar capable high pressure pump (GFP2.35) for a 4-cylinder 350 bar application [6]. Figure 3: Gasoline

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The PowerFlex high efficiency switch-mode power supply allows low voltage operation of the CPU down to 3 V, increasingly important with extensive use of engine stop/start operation. Finally, the Linear O2Flex ASIC supports the use of 2 wide-range lambda sensors. To account for the increased fueling accuracy requirements at ever shorter injection pulses, Delphi Technologies improved the ICLC function specifically with respect to injector opening detection. Figure 16 shows an overview on the ICLC principle and results at 600 bar fuel pressure.

Figure 16: ICLC principle and results at 600 bar fuel pressure

The upper left section of this figure illustrates that for the same electrical pulse length, the injector pintle displacement starts and finishes at different times, so injector opening and closing differs slightly. As fuel is injected when the pintle is lifted, pintle displacement correlates with the injected fuel mass. The lower left section shows the inflection in the injector low side voltage trace after the end of the injection pulse, induced by movement of the armature in the magnetic field of the injector coil. Extensive signal processing allows detection of the injector closing event from this voltage trace inflection. Injector opening is detected based upon the closing event at very short injection pulses. While the ICLC principle remains unchanged with increased fuel pressure, shorter pulse duration increases the accuracy requirements in the detection of both opening and closing. Thus, a lot of detail improvement was required in the ICLC algorithms. In addition, the Multec 16 injector was optimized for a stronger inflection of the voltage trace, especially at very short pulses to improve the opening and closing detection. The central part of Figure 16 shows ICLC results with a high number of new and severely aged injectors. Both graphs show the relative deviation in the injected fuel mass with respect to the fuel mass demand as calibrated in the injector flow curve in the ECU, covering fuel masses from the ballistic up to the beginning of the linear range. The upper graph shows the raw values without ICLC correction, while the lower graph shows the results for the same injectors after ICLC correction. It can be seen clearly that the fuel mass deviations are strongly reduced, especially in the ballistic region. The right part of this figure finally shows the statistical analysis of the ICLC improvement. Here, the relative standard deviation (3 σ) of the same injectors before and after ICLC

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rro

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] -

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600 bar, n-heptane

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correction is shown. The improvement of the fueling accuracy by ICLC is clearly visible, especially in the ballistic and transition region. Improving the fueling accuracy for high fuel masses requires a correction of the small differences in static flow between individual injectors, as differences in opening and closing are much less relevant in this region. Here, work is on-going to exploit the rail pressure drop during injection.

System Level Results

To understand the potential of fuel pressure to improve combustion performance, engine tests were undertaken on both a naturally aspirated single cylinder research engine (SCE) with central mount injector location as well on a large displacement turbo-charged 4-cylinder engine (MCE) with side mounted injectors. The first investigations performed on the SCE focused on how the fuel pressure influences the combustion knock intensity and the air-fuel mixing, and how these interactions might be used for improved engine performance. The multi-cylinder engine tests allowed brake specific values to also be investigated, thus including the effect of the fuel injection system frictional load, as well as all thermal and air-charge system interactions. The SCE measurements demonstrated that engine knock intensity can be reduced with a retarded start of injection timing (SOI) which allows the 50% mass fraction burned angle (MFB50) to be advanced at the same knock intensity limit. Figure 17 illustrates how to make use of this phenomena at 2500 rpm and 10 bar IMEP.

Figure 17: Injection pressure impact on injection timing at naturally aspirated high load

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deg]

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135180225270315360

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c]

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aust

[%]

Start of Injection [deg BTDC]

200bar

350bar

600bar

2500rpm, 10bar IMEP, Single Injection

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Each measurement point is calibrated with its knock limited spark advance, such that when the injection timing is retarded, the combustion phasing is advanced towards the maximum brake torque (MBT). Simultaneously there is a reduction in the time for mixing, and so there is a deterioration in the air-fuel mixing, which leads to an increase in both the particulate and the CO and HC emissions, represented here as combustion efficiency. The advantage of higher fuel pressures is an increase in the spray momentum and the air-fuel mixing rate, which reduces the penalty in air-fuel mixing from late injection timing. This then allows an effective use of later injection timings for improved combustion phasing and hence lower indicated specific fuel consumption (ISFC), and with equal or better PN. It is noted that the engine knock intensity was characterized from the high frequency filtered component of the cylinder pressure trace signal. The maximum peak to peak value of this signal was calculated for each cycle and then averaged over 100 cycles giving a “knock intensity” shown in Figure 18. The data clearly shows how engine knock intensity is reduced as the injection timing is retarded which may be attributed to the fact that less time is available for the chemical effects which lead to engine knock. Because of the higher resistance to knock, MFB50 can be advanced and higher maximum cylinder pressures tolerated at the same knock intensity limit.

Figure 18: Injection timing influence on knock intensity

For the multi-cylinder investigations a high pressure pump with internal seal was mounted on the engine to also assess the pump frictional losses. Both single and multiple injection strategies were investigated on this engine. The single injection results at 3000 rpm and 15 bar BMEP are shown in Figure 14. As was seen with the single cylinder with central mounted injector, there is a significant impact of the injection timing on the knock limited spark timing and MFB50. As the start of injection timing (SOI) is retarded from 380°CA to 300°CA the MFB10 to MFB90 is significantly reduced and the knock limited MFB50 can be advanced by ~5°CA improving the BSFC by up to 3%. As with the SCE results, the later injection timing can lead to a significant and unacceptable increase in the PN. Increasing the fuel pressure has several effects. First it tends to slightly increase the knock intensity at equal SOI, which may be attributed to its more rapid mixing. Second, it increases the engine friction, due to the higher load on the fuel pump. After controlling for differences in MFB50, a pressure increase from 200 to 500 bar increases BSFC by ~0.5%. However, the main effect of the higher pressure is to significantly improve the PN over almost the complete range of injection timings, and to improve the CO and HC at very late SOI timings. This advantage then allows a high pressure engine calibration at a fixed PN limit, to use later SOI timings, with more favorable MBF50 for an improvement in BSFC of up to 2%.

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SOI=320degSOI=300degSOI=280degSOI=260degSOI=240degSOI=220degSOI=200degSOI=180deg

Retarded Advanced

2500rpm, 10bar IMEP, Single Injection

Page 18: Delphi Technologies Next Generation GDi-System improved ......corresponding 400 bar capable high pressure pump (GFP2.35) for a 4-cylinder 350 bar application [6]. Figure 3: Gasoline

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Figure 19: Influence of SOI timing on combustion Single Injection at knock limit

The impact of high pressures with multi-injection strategies was further explored and results at 1500 rpm are shown in Figure 20. At lower engine speeds and high loads, a single injection is not the optimum calibration because of the lower in-cylinder air-motion and lower mixing and flame rates. The acceptable range of single injection SOI’s is limited from a PN perspective and even at high pressures there is little opportunity for significantly improved performance. However, by using a multiple injection strategy and retarding the 2nd injection timing late into the compression stroke a significant increase in the combustion speed and a reduction in the combustion duration is observed which again allows an advance of the knock limited combustion phasing. A BSFC benefit of up to 2% is observed versus the single injection calibration. This benefit is available at both 350 and 500 bar, however the PN emissions when using 500 bar can be greatly reduced. An additional desirable effect of the second injection is a significant reduction in the cycle to cycle variation of IMEP (CoV).

Figure 20: Single vs Double Injection at the knock limit and SOI for best BSFC

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1500rpm, 15bar BMEP, E10, Single & Double Injection (Qsplit: 70/30), SOI for Best BSFC

Page 19: Delphi Technologies Next Generation GDi-System improved ......corresponding 400 bar capable high pressure pump (GFP2.35) for a 4-cylinder 350 bar application [6]. Figure 3: Gasoline

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The improved atomization with higher fuel pressure offers the opportunity for a wider usage of multi-pulse injection strategies leading to an overall positive trade-off between particulate emissions, fuel consumption and combustion stability. Based on single-cylinder and multi-cylinder engine test results various driving cycle simulations were performed to estimate the trade-off of higher fuel pressure and fuel consumption for homogeneous stoichiometric combustion (see Figure 21). The green and orange areas represent the range of fuel consumption benefit on the WLTC cycle as fuel pressure is increased from 100bar. The higher fuel pressure requires a higher drive torque at the camshaft. Compared to a conventional pump, the pump with PRS causes a slightly higher torque loss at low fuel pressure, but has significantly lower parasitic losses at higher pressure. The difference in losses between these pumps is represented by the orange area in the diagram. A thermodynamic efficiency benefit was also observed in the engine results and is estimated at between 0.5 and 1.0% for a pressure rise from 350 to 500 bar. This range in thermodynamic efficiency benefit is represented by the green area in the diagram. Overall, for a system pressure increase from 350 to 500 bar a fuel consumption benefit up to 1% may be expected.

Figure 21: Pressure Impact on Particle Number and Fuel Consumption

For the particulate emissions the values are again consolidated from single and multi-cylinder combustion results performed on stabilized injectors run at mid-speed steady state conditions. A similar sensitivity of PN to pressure has been seen at other speeds and loads, although the absolute values are different. These results demonstrate the expected strong dependence of PN on fuel pressure. While a steep decrease is observed between 200 and 350 bar the response tends to flatten and the absolute improvement between 500 and 600 bar is limited. An overall improvement in the emissions and efficiency trade-off can already be achieved with an existing combustion system without modifications on spray characteristics nor engine hardware. However, in order to realize the full potential of the proposed fuel pressure increase, typical combustion development work with an optimization of the key engine design and injection system parameters is necessary. As presented in the previous chapters the required fuel system components to make this work are already available.

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]

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Page 20: Delphi Technologies Next Generation GDi-System improved ......corresponding 400 bar capable high pressure pump (GFP2.35) for a 4-cylinder 350 bar application [6]. Figure 3: Gasoline

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Summary and Conclusion

The engine results presented in this paper underline the potential and value of a further fuel pressure increase for more efficient and cleaner gasoline engines. With increasing injection pressure the levels of particulate numbers are significantly reduced and this beneficial behavior is observed also for very small particles in the range of less than 23 nm which may become important for even more stringent particulate emission regulations of the future. The new components for fuel pressures up to 600 bar are an evolution of today’s production components with specific packaging neutral design modifications to cope structurally and functionally with the higher fuel pressure. The roadmap in Figure 22 shows the timing as well as underlines the availability of validated key components and the systems well before the introduction of the “post Euro 6d” legislation expected around 2025.

Figure 22: Delphi Technologies – Gasoline Direct Injection Roadmap

Delphi Technologies Next Generation GDi-System will support car manufactures to meet future stringent emissions standards at a controlled cost for the worldwide market.

Literature

[1] United Nations Framework Convention on Climate Change (UNFCCC):

COP24 - Katowice Climate Change Conference – December 2018, https://unfccc.int/katowice

[2] VW kündigt Ende von Verbrennungsmotoren an; Quelle: ZEIT ONLINE,

04DEC2018; https://www.zeit.de/wirtschaft/unternehmen/2018-12/elektromobilitaet-vw-ausstieg-verbrennertechnologie-2026-elektroantrieb-benzin-diesel

[3] M. VÖGLER, A. KÖNIGSTEIN, N. FUHRMANN, C. BEIDL, M. THIEM:

Combustion Engines for Electrified Powertrains – Systems Engineering

Multec 12 – 200 bar

Multec 12.1 – 250 bar

Multec 14 – 400 bar

GFP2.40 – 400 bar

GFP1.20 – 200 bar

MT92

past 2019 2020 2021 2022

GFP3.x – 500+ bar

Multec 16 – 500+ bar

Forged Rail - 350 bar & higher pressures

2023 future

GCM8.X

GCM7

Page 21: Delphi Technologies Next Generation GDi-System improved ......corresponding 400 bar capable high pressure pump (GFP2.35) for a 4-cylinder 350 bar application [6]. Figure 3: Gasoline

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between Efficiency, Emission and Cost; 27th Aachen Colloquium Automobile and Engine Technology 2018

[4] BERNDORFER A., BREUER S., PIOCK W.F., VON BACCHO P.:

Diffusion Combustion Phenomena in GDi Engines caused by the Injection Process; SAE 2013-01-0261

[5] W.F. PIOCK, G. HOFFMANN, G. M. RAMSAY, R. MILLEN, S. SCHILLING, D. N. DALO, J. G. SPAKOWSKI: Delphi’s Fuel Injection Systems for Efficient and Clean Gasoline Engines with Direct Injection; 36th Vienna Engine Symposium, 2015

[6] F. EICHLER, W. DEMMELBAUER-EBNER, J. THEOBALD, B. STIEBELS, H.

HOFFMEYER, M. KREFT: The New EA211 TSI® evo from Volkswagen; 37th Vienna Engine Symposium, 2016

[7] B. BEFRUI, G. HOFFMANN, P. SPIEKERMANN, W.F. PIOCK: A Comparative

Study of the Fuel Pressure and Temperature Effects on the GDi Multi-Hole Spray; 10. Tagung Diesel- und Benzindirekteinspritzung 2016, Springer Vieweg Verlag

[8] A. BOSSI, G. HOFFMANN, J. SHI: Optimization of next generation high flow

Gasoline Direct Injection; 11. Tagung Diesel- und Benzindirekteinspritzung 2018, Springer Vieweg Verlag

[9] J. SHI, E.G. SANTOS, G. HOFFMANN, G. DOBER; Large Eddy Simulation

als effektives Werkzeug für die GDi-Düsenentwicklung, MTZ 10/2018 [10] J. G. SPAKOWSKI, J. KAZOUR, B. KASWER, T.D. SPEGAR: GDi High

Efficiency Fuel Pump for Fast Engine Starts and Reduced Cam Loads, SAE 2019-01-1196