400 Commonwealth Drive, Warrendale, PA 15096-0001 U.S.A. Tel: (724) 776-4841 Fax: (724) 776-0790 Web: www.sae.org

SAE TECHNICALPAPER SERIES 2008-01-0941

The Impact of Injection Strategies onEmissions Reduction and PowerOutput of Future Diesel Engines

Gavin Dober, Simon Tullis, Godfrey Greeves, Nebojsa Milovanovic,Martin Hardy and Stefan Zuelch

Delphi Diesel Systems

Reprinted From: Diesel Fuel Injection and Sprays, 2008(SP-2183)

2008 World CongressDetroit, MichiganApril 14-17, 2008

By mandate of the Engineering Meetings Board, this paper has been approved for SAE publication uponcompletion of a peer review process by a minimum of three (3) industry experts under the supervision ofthe session organizer.

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, ortransmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise,without the prior written permission of SAE.

For permission and licensing requests contact:

SAE Permissions400 Commonwealth DriveWarrendale, PA 15096-0001-USAEmail: permissions@sae.orgTel: 724-772-4028Fax: 724-776-3036

For multiple print copies contact:

SAE Customer ServiceTel: 877-606-7323 (inside USA and Canada)Tel: 724-776-4970 (outside USA)Fax: 724-776-0790Email: CustomerService@sae.org

ISSN 0148-7191Copyright © 2008 SAE InternationalPositions and opinions advanced in this paper are those of the author(s) and not necessarily those of SAE.The author is solely responsible for the content of the paper. A process is available by which discussionswill be printed with the paper if it is published in SAE Transactions.

Persons wishing to submit papers to be considered for presentation or publication by SAE should send themanuscript or a 300 word abstract of a proposed manuscript to: Secretary, Engineering Meetings Board, SAE.

Printed in USA

ABSTRACT

Future light, medium and heavy duty diesel engines will need to satisfy the more stringent emission levels (US 2014, Euro 6, etc.) without compromising their current performance and fuel economy, while still maintaining a competitive cost. In order to achieve this, the Fuel Injection Equipment (FIE) together with the pressure charging, cooling system, exhaust after treatment and other engine sub-systems will each play a key role. The FIE has to offer a range of flexible injection characteristics, e.g. a multiple injection train with or without separation, modulated injection pressures and rates for every injection, higher specific power output from the same injector envelope, and close control of very small fuel injection quantities.

The aim of this paper is to present Delphi’s developments in fuel injection strategies for light and medium duty diesel engines that will comply with future emission legislation, whilst providing higher power density and uncompromised fuel economy.

INTRODUCTION

The market improvement of Diesel vehicles is closely linked to the continuous improvement in its perception to customer and benefits such as drivability, increased power density and improved fuel consumption. One of the main contributors to this is significant improvement in Fuel Injection Equipment (FIE). During the recent years, sales of passenger cars powered with direct injection Common Rail (CR) FIE have gained a noticeable increase in market share in Europe to over 50% (or more than 8 million vehicles annually) [1]. Diesel engines for passenger cars, medium and heavy duty vehicles and off-road applications need to meet future stringent emission regulations, as proposed in areas such as the USA, Japan and Europe. In particular there is a need to reduce the emissions of NOx and particulate matter (PM) over the appropriate emission test cycle.

In general it is beneficial to further develop the diesel engine combustion system to provide further reductions in engine-out NOx and PM emissions, even when exhaust aftertreatment systems are to be used. For example, in-cylinder combustion improvements can help to reduce the urea consumption needed for the Selective Catalytic Reduction (SCR) system and/or reduce the required frequency of regeneration for a Diesel Particulate Filter (DPF) system. Also there is a continuing demand to increase the engine torque and rated power output and to reduce the engine fuel consumption which also impacts CO2 emissions. The search for better combustion in the field of diesel engines has been strongly linked to the capability of the FIE to generate high injection pressures which gives faster fuel-air mixing and lower soot formation allowing an overall better emissions and performance trade off. CR systems provide a significant increase in injection pressure capability compared with previous rotary and inline pump systems and also provide electronic control of the level of injection pressure across the engine speed and load range [2]. The CR system can also provide a flexible choice of multiple injections that can be used to explore potential benefits including a pilot that is necessary to mitigate the tendency for higher combustion noise with the relatively square diagram of a CR system. Also multiple injections can be used to facilitate various forms of advanced combustions (low temperature, premixed or partially-premixed) to achieve very low NOx and soot at least for part load conditions [3, 4].

The performance of the CR system has been continually refined over the last several years. In order to maintain precise injection control and minimize dispersion between vehicles, innovative software strategies have been developed including Accelerometer Pilot Control (APC) and Individual Injector Calibration (I3C) [5]. Simultaneously there is a continuous request to increase the maximum pressure capability of CR systems. The

2008-01-0941

The Impact of Injection Strategies on Emissions Reduction and Power Output of Future Diesel Engines

Gavin Dober, Simon Tullis, Godfrey Greeves, Nebojsa Milovanovic, Martin Hardy and Stefan Zuelch

Delphi Diesel Systems

Copyright © 2008 SAE International

latest light duty systems are capable of 2000bar, and will be capable of > 2000bar in the near future.

The aim of this paper is to present developments in FIE and fuel injection strategies for light and medium duty diesel engines that will comply with future emission legislation, whilst providing higher power density and uncompromised fuel economy.

EXPERIMENTAL APPARATUS AND PROCEDURES

ENGINE SET-UP

Two single cylinder engines with similar configurations were used for test work presented here. The engine details are listed in Table 1. The engines versions 1 and 2 used for this work both have a 4-valve cylinder head with variable swirl capability although the lowest level of swirl (∼ 2.0 on the momentum meter method) was used for tests presented here. The engines were run with an external pressure charging system to control the boost pressure, temperature and Exhaust Gas Recirculation (EGR) level. Values were chosen based on a 2.0 and 2.1 litre, 4cylinder, Variable Geometry Turbine (VGT) equipped engine. Comparisons have been made between these engines and multi-cylinder engines to estimate a friction correction factor [6]. This factor has been applied to all estimates of BMEP.

The engines were mounted on a steady state test bed and were fully instrumented for the measurement of performance, smoke (AVL 415S heated smoke meter for filter smoke number - FSN) and gaseous emissions (Horiba MEXA 7100 DEGR). Fuel consumption was measured by a gravimetric method (using an AVL 733 fuel meter). The CO2 measurements were made in the exhaust and were used to calculate changes of airflow, and hence levels of EGR. The soot emissions were not measured directly but estimated from the smoke using the AVL correlation.

FUEL INJECTION EQUIPMENT

The FIE used were Common Rail systems with the maximum pressure of 2000bar. The pump was a three-plunger Diesel Fuel Pump (DFP 3 family) [7], which was electrically driven on engine 1 and engine mounted on engine 2. As flow rates through the pump are four times lower than normal on a single cylinder engine some uncertainty exists over the friction characteristics with the engine driven pump. For this reason only indicated specific performance is presented with engine 2.

The fuel injectors used were: MultecTM Solenoid Injector (DFI 1 family) and a Direct Acting Injector (DFI 3 family). The operational schematics of these injectors are shown in Figure 1.

Figure 1. MultecTM Solenoid and Direct Acting CR Injectors

MULTECTM DFI 1 INJECTOR – This solenoid injector is based on a unique design with balanced servo valve technology. The small size of this valve/actuator allows it to be packaged in-line and in close proximity to the needle providing fast actuation and precise metering. With this approach closing and opening of the servo valve can be completed, depending on model (DFI 1.1 – 1.5), within 100-250 μsec [5]. This performance, with the proven durability of the solenoid actuation principle, is equal or better than the servo-piezo driven injector technologies currently available. The compact DFI 1 injector requires less force to operate (20N) and therefore less energy, so the standard voltage supply of 12 V available from the battery is sufficient. The elimination of the control piston (a device that connects the control chamber with the needle-Figure 1) provides the potential to reduce back-leakage, which improves

Needle

Motion Amplifier

Piezo-ceramic Acutator

Nozzle

DFI 3 Concept Direct Acting Control

Low Pressure Return

DFI 1 Concept Balanced Servo Solenoid

Control Piston

Actuator (Solenoid)

High Pressure Control

Needle Nozzle

Spray

Pressure Balanced

Valve

Engine 1 Engine 2

Engine Type 4 stroke diesel Light Duty Direct Injection 1 cylinder Research

4 stroke diesel Light Duty Direct Injection 1 cylinder, Research

Bore x Stroke Swept Volume Compression Ratio

85 x 89 mm 0.5 litres 16.5:1

85 x 94 mm 0.533 litres 16:1

Cylinder-head 4 valve variable swirl

4 valve variable swirl

Fuel Injection Common Rail Injectors: -MultecTM Solenoid (DFI 1 family) -Direct Acting (DFI 3 family)

Pump Mounting Electrically Driven

Engine mounted

Table 1. Engine details

hydraulic efficiency and reduces the amount of cooling required on the fuel return path.

DIRECT ACTING DFI 3 INJECTOR – In comparison to conventional servo (solenoid or piezo) hydraulic injectors, the DFI 3 operates with completely different technology. This technology eliminates the usual four-step servo hydraulic concept (actuation of the solenoid/piezo, opening the servo valve, release of the pressure from the control chamber through a restriction/orifice and opening the needle) down to a single step: The direct actuation of the needle through a hydraulic amplifier by a piezo-ceramic actuator (Figure 1).

The DFI 3 concept allows both a fast and controlled opening and closing of the nozzle needle independent of rail pressure. This is possible because unlike a servo-controlled injector, the force change needed for needle opening is provided by a piezo-actuator that is decoupled from the rail pressure supply. It is therefore possible to adapt the force change delivered by the actuator electronically as required. This leads to an improved multiple injection capability. This injector contains an internal volume of fuel, and does not have any back-leak. The absence of a back-leak simplifies the installation and eliminates the need for fuel return lines and fuel coolers even when operating at 2000 bar. It also reduces the parasitic losses in the high pressure pump thus giving a potential fuel economy benefit.

Hydraulic performance of DFI3 –The hydraulic performance of the direct acting injector DFI 3 is improved over servo injectors. The maximum needle speed approaches 3 m/s while servo injectors normally operate at approximately 1 m/s. The needle speed of DFI3 is not dependent on rail pressure and so is maintained even at very low rail pressures (Figure 2). The other feature to note is the maintenance of high line pressure, on the entrance to the injector, even after the start of injection (Figure 3). This is due to a volume of fuel stored within the injector, and due to the absence of a back-leak from the injector. The improved stability of rail pressure then leads to a consistent injection rate for the full injection duration (Figure 2).

Figure 2. Injection rate at different rail pressures and constant duration with DFI3

The overall result is an injection rate which approaches an ideal square wave. This provides the potential for much better spray formation, particularly at low rail pressures and for very small injection quantities (0.5 mg). It also allows a shorter injection period for the same rail pressure and injection quantity [5].

Another advantage of the volume of fuel in the injector and the absence of a back-leak is a reduction in the size of pressure oscillations in the pipe leading into the injector. When combined with the fast needle speed, which is independent of rail pressure, the interaction between pilot quantity and separation and main quantity is reduced (Figures 3 and 4). This feature increases the flexibility of operation of the injection in terms of the range and number of injections. Pilot-main separation can consequently be varied to find the optimum separation from a combustion stand-point rather than the optimum from a hydraulic stand-point.

0

10

20

30

40

50

60

0 0.5 1 1.5 2 2.5

Time after start of Injection (ms)

Inje

ctio

n r

ate

(mg

/ms)

0

400

800

1200

1600

2000

Rai

l pre

ssu

re (

bar

)

Servo injectorDirect acting

Figure 3. Pressure drop in high pressure pipe at entry to the injector at 2000 rpm

22

26

30

34

38

0 0.5 1 1.5 2 2.5 3Hydraulic separation (ms)

Del

iver

y (m

g)

Servo InjectorDirect Acting

Figure 4. The effect of pilot-main separation on total fuel quantity at constant demand

Engine performance of DFI3 – With the square rate profile the injector can provide more fuel in a shorter period of time, which leads to an enhancement in the engine performance as can be seen from results in Figure 5. The results were obtained on Engine 1 for full load rated speed at constant maximum cylinder pressure and exhaust temperature.

The fast operation of the nozzle needle brings an improvement in the spray momentum, which in turn increases the rate of fuel break-up and air entrainment.

Figure 5. Engine performance comparison servo injector vs direct acting at 4200rpm

This improves the mixing within the fuel jet (i.e. increasing the rate of fuel-air mixing) and hence reduces the smoke emissions (Figure 5). This feature, together with a needle speed which is independent of the rail pressure, gives an additional freedom for the engine calibration to achieve emission targets without compromising fuel consumption

As the emissions legislative cycles (NEDC, FTP and Japan 10-15) are largely concentrated in the part load region, then there is a scope for improvement in emissions with using different injection, air and EGR strategies. This will be explained in more detail later in the text.

RESULTS AND DISCUSSION

MULTIPLE EARLY INJECTIONS

Two of the key features of the direct acting injector, as previously discussed, are the independence of the needle speed from rail pressure and a very low interaction between injection events. These features

imply benefits for the injection of small quantities at low rail pressures as a much greater proportion of the fuel will be injected with a fully open needle and consequently with the best spray structure when compared to a servo injector.

0

1500

3000

4500

CO

[p

pm

]0

600

1200

1800

TH

C [

pp

m]

0.0

0.3

0.6

0.9

1.2

SM

OK

E (

FS

N)

210

218

226

234

0 4 8 12 16 20 24 28 32 36 40 44

NOx [ppm]

ISF

C [

g/k

Wh

]

DFI3 - single injection - 600bar RP - EGR swing

DFI3 - triple injection - 850bar RP - EGR swing

Figure 6. 1380rpm, 1.1bar BMEP: Reduction of THC and CO at equivalent smoke with triple injection strategy (Injection timings vary with EGR over the range of 18ºBTDC to 1ºBTDC)

Furthermore, the low interaction allows an increase in the flexibility in delivery of multiple injection events and the minimum separation time between two injections can, if necessary be reduced even to 0 μsec [5]. This gives the potential to perform close coupled multiple injections (i.e. ‘injection trains’) that could be more suitable for the advanced types of combustion (low temperature, premixed, partially premixed, etc.). Some of these results are presented in Figures 6 and 7, which show very low NOx concentrations achieved using an advanced type of combustion. The tests were performed on Engine 2 with the DFI 3. Minimum NOx emissions were reached using very high levels of EGR (43% - 64%) and by injecting early enough so as to avoid diffusion combustion. This was all done at a constant boost pressure and combustion timing.

228

232

236

240

244

BS

FC

(g

/kW

h)

Servo Injector

Direct Acting

-3%

0.0

0.5

1.0

1.5

Sm

oke

(F

SN

)

-30%

17.0

17.5

18.0

18.5

19.0

1500 1600 1700 1800 1900 2000 2100

Rail Pressure (bar)

BM

EP

(b

ar)

+5%

0

1500

3000

4500

CO

[p

pm

]

220

235

250

265

0 4 8 12 16 20 24 28 32 36 40 44

NOx [ppm]

ISF

C [

g/k

Wh

]

DFI3 - single injection - 250bar RP - EGR swing

DFI3 - triple injection - 250bar RP - EGR swing

0.0

0.1

0.2

0.3

0.4S

MO

KE

(F

SN

)

0

600

1200

1800

THC

[ppm

]

Figure 7. 1480rpm, 2.5bar BMEP: Improvement in THC emissions with triple injection strategy (injection timings vary with EGR over the range of 28ºBTDC to 4ºBTDC) As can be seen in the results, the emissions of THC and CO are several times higher than would be produced with conventional combustion. A typical solution is to use after treatment (Diesel Oxidation Catalyst) to clean up these emissions, however this can be difficult when the loads and hence the exhaust temperatures are very low. The increase in THC and CO emissions is a result of generally lower combustion temperatures with advanced types of combustion using high EGR for very low NOx. Also since the fuel is injected early it has time to mix before combustion starts. Inevitably, some fuel may mix to an over-lean condition (i.e. lean pocket of over-mixed fuels can exist) and not reach a high enough temperature giving a source of high THC and CO [8, 9]. Also with very early injection there is the possibility of liquid impingement depending on test conditions. Therefore, a fine control is required over the injection timing and the mixture formed to avoid excessively high THC and CO. Ideally this can be achieved using different injection strategies. This approach was trialed on this engine with both a variation of rail pressure and multiple injection strategies.

Reducing the rail pressure effects the penetration of the spray, thus effecting mixing, but it also typically lowers the momentum and mixing energy. This can result in an increase in the soot emission [8]. An alternative solution is to use a multiple injection strategy to reduce penetration. This can also be done in conjunction with reduced rail pressures (∼250 bar instead of 450 bar) for the lowest load (Figure 6) or at increased rail pressures as the load increases (Figure 7). With triple injection but with the lower rail pressure the THC is reduced by ~ 55-60% and CO by ~ 25-40% dependent on EGR when compared with a single injection strategy. As expected the noise is also reduced by ~5dBA and specific fuel consumption is improved by ~ 8%. This improved performance is attributed to a more even fuel-air mixture with the multiple injection strategy.

With triple injection at 2.5bar BMEP the rail pressure was increased up to 850bar (Figure 7). Higher rail pressures were more advantageous at the higher loads to increase the rate of fuel-air mixing before combustion begins. This calibration produced an improvement in emissions over the single injection strategy. CO was reduced by ~ 0-20% and THC by ~ 40-60% dependent on EGR level. Noise was also reduced by ~ 0-2dB, which was a smaller amount than at the lower load and probably due to the higher injection pressures. Specific fuel consumption was also improved in the range of ∼ 0-2%. These improvements are attributed to the increased freedom in the separations between the multiple injections as subsequent injections are relatively independent of the previous injection [5].

0.0

1.0

2.0

3.0

4.0

5.0

SM

OK

E [

FS

N]

180

190

200

210

0 20 40 60 80 100 120 140 160 180 200NOx [ppm]

ISF

C [

g/k

Wh

]

Ref - Std Boost - 930bar RP

DFI3 - Std Boost - 800bar RPDFI3 - Std Boost - 1250bar RP - EGR swing

DFI3 - Adv Boost - 1200bar RP - EGR swingDFI3 - Adv Boost - 1600bar RP - EGR swing

DFI3 - Adv Boost - 2000bar RP

Figure 8. 1935rpm, 9.1bar BMEP: Potential for ultra-low NOx at mid load

At medium to high loads a more conventional combustion strategy has to be used. However, the use of high levels of cooled EGR still allows very low NOx levels to be reached although there is a more typical NOx – Soot trade-off (Figure 8) [10]. The improvements in the NOx-Soot trade-off are due to the improved opening and closing characteristics of the direct acting injector. For the same smoke level and a lower rail pressure NOx can be reduced by ∼15% (from 180ppm to 153ppm) by using more EGR. This is possible since the DFI 3 injector provides higher spray momentum, particularly during the opening and closing phases of the injection event and therefore allows additional EGR to be tolerated. A small increase in rail pressure allows further increase in EGR and improves NOx to 110ppm.

A 2-stage turbo charging system might be expected to allow an increase in the absolute inlet manifold pressure from 1.7bar to 2.2bar. This increased boost allows an increase in the maximum EGR from 26% to 38%, which enables a further NOx reduction to 70ppm at 1200bar rail pressure and while keeping soot constant. Increasing the rail pressure reduces the NOx further and finally with the system maximum of 2000bar and high levels of boost EGR may be increased to 45%, which reduces NOx to less than 30ppm. There is, as expected, a noise penalty to using such high rail pressures but this exercise is intended to demonstrate the possibilities rather than attempting to be a final solution. It is also important to note that indicated specific fuel consumption (ISFC) does not deteriorate as the NOx is lowered. It does instead show a strong improvement of up to 10% over the reference. However, due to the increase in pump parasitic losses with the higher rail pressures, the actual brake specific improvement is likely to be only around half this value.

MULTI-MODE CYCLE SIMULATION

An engine optimization was performed with both injectors (DFI1.3 and the DFI3) with the objective of meeting forthcoming worldwide emissions levels and minimizing the need for NOx after-treatment. The NEDC emissions cycle was simulated with 12 key steady state modes. It can be seen that both injectors gave good results (Figure 9).

The DFI3 offers additional benefits in both NOx and soot over a range of different speeds and loads, even when it uses a larger nozzle size (0.8 l/min vs 0.6 l/min). This makes DFI3 more suitable for a range of challenging high performance/high vehicle weight applications, and gives the potential for reductions in CO2 emissions.

The only apparent deficiency of the DFI3 system is at mode11. It should be pointed out that this is a medium load point of 7.4bar BMEP where the size of the nozzle is of critical importance. The DFI3 suffers somewhat because of the choice of a larger nozzle flow.

0.0000

0.0015

0.0030

0.0045

Wei

gh

ted

NO

x (g

/km

)

0.0000

0.0005

0.0010

0.0015

0.0020

Wei

gh

ted

So

ot

(g/k

m) DFI1, Nozzle flow 0.6l/min

DFI3, Nozzle flow 0.8l/min

0.00

0.05

0.10

0.15

Wei

gh

ted

CO

(g

/km

)

0.00

0.02

0.04

0.06

0 1 2 3 4 5 6 7 8 9 10 11 12

Test Mode

Wei

ghte

d H

C (g

/km

)

Figure 9. NEDC simulated vehicle performance with 12 modes, (Engine 1, engine-out emissions; class C, 1600kg vehicle mass) It should be noted that these results only show the potential of both injectors to achieve forthcoming emissions level. To do so robustly across millions of vehicles and over the life of the vehicles, still requires development and validation in transient controls, closed loop strategies and tolerance reduction which will be explored in future papers.

RATE SHAPING

As indicated earlier in this paper, when using an injector with a very fast needle opening and closing (i.e. speed of ∼ 3 m/s) there is a slightly higher level of noise when compared to a servo system with the same injection strategy. The reason for the higher noise is an increase in the fuel quantity injected during the ignition delay period and consequently a larger proportion of premixed combustion. It is possible to mitigate this with multiple injections. As DFI3 has potential for multiple injections with a short separation time, then there is the possibility to increase the number of pre-injections (to 2 or 3) to reduce noise [11]. However, this introduces additional calibration work which it would be better to avoid.

Since the actuation of the needle is only dependent on the piezo-ceramic stack voltage then a large amount of freedom is available to control the opening and closing

rates of the injector. A first attempt at a noise reducing strategy was to slow the opening rate of the injector by using the conventional approach of slowing down the needle opening velocity. The results were shown to reduce noise, however they also increased the soot. This is assumed to be due to deterioration in spray momentum efficiency, during the low/slow needle lift period that led to poor fuel-air mixing inside the combustion chamber, as was also discussed by Reitz et al [12].

It was subsequently postulated that noise could be reduced independently of smoke by using a dual opening rate strategy. Initially the injector would be opened fast and then the needle velocity would be slowed (Figure 10). It was anticipated that this would allow a minimization of the momentum efficiency loss and of the poorly formed sprays at the start of injection, but still maintain enough needle seat throttling to reduce the quantity of fuel injected during the ignition delay. This would then lead to a reduction in the amount of noise produced without compromising mixing.

Figure 10. Hydraulic test bench data for dual opening rate strategy at 1200bar

20

40

60

80

100

120

-20 -10 0 10 20 30

Crank Angle Degrees (ATDC)

Cyl

ind

er P

ress

ure

(b

ar)

Sta

ck V

olt

age

NormalSlowerSlowest

Figure 11. Dual opening rate at 2800rpm/10.4bar BMEP (1000bar rail pressure; Engine 1)

Table 2. Emissions and Noise with dual opening injection rates

Injection Rate

NOx (ppm)

Smoke (FSN)

Noise (dBA)

THC (ppm)

Delivery (mg)

Normal 371 0.143 93.7 99 38.8 Slower 371 0.151 92.6 105 38.7 Slowest 371 0.154 89.5 99 38.7

The effect of this strategy is illustrated in Figure 11 and Table 2. The results, obtained at 2800rpm and 10.4bar BMEP, show a 4.2dBA reduction in combustion noise at equivalent NOx with little or no change in smoke performance.

86

90

94

98

102

0 0.08 0.16 0.24 0.32Pilot Quantity (ms)

Co

mb

ust

ion

no

ise

(dB

A) Normal

SlowerSlowest

Pilot-Main Separation = 0.22ms

Figure 12. Effect of pilot quantity and dual opening rate on noise at 1400rpm, 3.4bar BMEP (Engine 1)

86

90

94

98

102

0 0.08 0.16 0.24 0.32Pilot Quantity (ms)

Co

mb

ust

ion

no

ise

(dB

A)

NormalSlowerSlowest

Pilot-Main Separation = 0.16ms

Figure 13. Effect of pilot quantity and dual opening rate on noise at 2150rpm, 7.4bar BMEP (Engine 1) This noise benefit extends to using pilots as can be seen in Figures 12 and 13. The new strategy leads to a lower minimum noise level at both low and medium loads. Additionally the injector control is more robust with the level of noise being less sensitive to the pilot quantity.

CONCLUSIONS

The existing Common Rail MultecTM DFI 1 family and next generation Direct Acting DFI 3 family have been designed to minimize the need for NOx after-treatment for forthcoming emission regulations. The DFI 3 is particularly suitable for the high power and performance heavier-vehicle applications demanded by the market.

The key attributes of the Direct Acting system are as follows:

• Designed for 2000 bar capability • Fast needle operation resulting in simultaneous

power increase and soot and NOx emissions reduction.

• Enhanced multiple injection capability (0.5 mg minimum quantity and 0μs separation)

• Variable needle velocity capability, hence enabling various rate shaping capabilities

• No back-leak, hence operations without back-leak lines

• Potential for operation without a fuel cooler • The potential for improved fuel consumption • Operation with the existing pump capacity These potentials provide a competitive advantage for next generation of passenger car diesel engines in competition with turbo charged downsized gasoline engine and improved hybrid engines. ACKNOWLEDGMENTS

The authors would like to thank Detlev Schoeppe, Engineering Director for his support and comments. Thanks are also due to AVL GmbH for their excellent work in generating the results presented from engine 2.

REFERENCES

1. US DoE, FreedomCAR & vehicles technologies Program, fact sheet no. 481, Aug 2007.

2. Ganser M A, “Common rail injectors for 2000 bar and beyond”, SAE 2000-01-0706.

3. Montgomery D T, Reitz R D, “Effects of multiple injections and flexible control of boost and EGR on emissions and fuel consumption of a heavy-duty diesel engine”, SAE 2001-01-0195, 2001.

4. Hardy W L, Reitz R D, “An experimental investigation of partially premixed combustion strategies using multiple injections in a heavy-duty diesel engine”, SAE paper 2006-01-0917.

5. Schoeppe D, Spadafora P, Guerrassi N, Greeves G, Guerts D, “ Diesel common rail technology for future high power and low emission standards “, Dresden 2005.

6. Tullis S, Greeves G, HSDI emission reduction with common rail FIE, IMechE 1999 S492/S18.

7. Jorach, R. W.; Schöppe, D.; Nevard, R. T.; Thornthwaite, I. R.; Wilson, N. D.: Delphi’s 2000 bar

common rail development for the Multec™ diesel common rail system. In: Internal Combustion Engines: Performance, Fuel Economy and Emissions, 11. – 12.12.2007. Editor: IMechE London 2007

8. Khan I M, Greeves G, Wang C H T, “Factors affecting smoke and gaseous emissions from direct injection engines and a method of calculation”, SAE 730169.

9. Miles, P., Sources and mitigation of CO and UHC emissions in low-temperature diesel combustion regimes: Insights obtained via homogeneous reactor modeling, DEER 07 Conference, Detroit, 13-16 August, 2007.

10. Heywood J B, Internal combustion engine fundamentals, McGraw-Hill, New York, 1988.

11. G. Bression, D Soleri, S Savy, S Dehoux, D Azoulay, H Hamouda, L Doradoux, B Bastardie, N Lawrence “Reduction of THC and CO emissions at low load for HCCI diesel combustion”, 6th Symposium towards clean diesel engine – Napoli, June 20-22nd 2007.

12. H Juneja, Yl Ra and R D Reitz, “Optimization of Injection Rate Shape Using Active Control of Fuel Injection” SAE 2004-01-0530.

CONTACT

Gavin Dober, PhD BEng, BSci Senior Development Engineer Combustion Department Delphi Diesel Systems Courteney Road Gillingham Kent, UK ME8 0RU Email: gavin.dober@delphi.com Tel +44(0)1634 874639

DEFINITIONS, ACRONYMS, ABBREVIATIONS

ATDC After Top Dead Centre

BMEP Brake Mean Effective Pressure

BSFC Brake Specific Fuel Consumption

BTDC Before Top Dead Centre

CO Carbon Monoxide

CO2 Carbon Dioxide

CR Common Rail

DEG Degrees

DPF Diesel Particulate Filter

EGR Exhaust Gas Recirculation

FC Fuel Consumption

FIE Fuel Injection equipment

FSN Filter Smoke Number

IMEP Indicated Mean Effective Pressure

ISFC Indicated Specific Fuel Consumption

I3C Individual Injector Calibration

NEDC New European Drive Cycle

NOx Oxides of Nitrogen

PM Particulate Matter

PPM Parts Per Million

RP Rail Pressure

RPM Revolutions Per Minute

RS Rig swirl number

SCR Selective Catalytic Reduction

SFC Specific Fuel consumption

TDC Top Dead Center

THC Total Hydrocarbon

VGT Variable Geometry Turbine