Development of Engine Management System for a

Common-Rail Diesel Engine with Cylinder Pressure

Measurement

Chia-Jui Chiang, Chih-Cheng Chou,

Ying-Wei Lin and Tzung-Hua Tsai

Department of Mechanical Engineering

National Taiwan University of Science and

Technology

Taipei, Taiwan

Email: cjchiang@mail.ntust.edu.tw

Yong-Yuan Ku

Emission and Fuel Economy Testing

Automotive Research and Testing Center,

Changhua, Taiwan

Email: tom@artc.org.tw

Abstract—Common-rail injection systems allow precise and

flexible control of the fuel injection timings and injected fuel

amount, resulting in improved fuel economy and reduced

emissions. In this paper, an engine management system (EMS) is

developed for a common-rail (CR) diesel engine. A common-rail

test bench is used to facilitate the control development and

calibration of the fuel injection system. The common-rail

pressure (CRP) is controlled with a feedforward plus feedback

control structure. Real-time calculation of the combustion heat

release rate (HRR) is conducted based on the cylinder pressure

measurement to examine the control performance with various

rail pressures, injection timings and injection pulse widths

(IPWs). Experimental results show that the heat release process

can be precisely controlled by the injection timing. In the future,

the developed EMS can be used for closed-loop combustion

control with cylinder pressure feedback. Keywords—Engine Management System (EMS); Common-rail

(CR) diesel engine; Heat release rate (HRR); Exhaust gas

recirculation (EGR)

I. INTRODUCTION

Diesel engine is characterized with irreplaceable advantages

such as high fuel efficiency and high torque output and thus is

one of the best choices for heavy-duty vehicles [1], [2]. The

nitrogen oxides (NOx) and particulate matter (PM) emissions

of diesel engine, however, are in general higher than those of

gasoline engine [1], [2], [3]. Modern diesel engines containing

the common-rail (CR) fuel injection systems, the variable

geometric turbochargers (VGTs) and the exhaust gas

recirculation (EGR) systems allow further improvement on the

performance and reduction of pollutant emissions, noise and

fuel consumption [1], [3], [4], [5], [6]. Accomplishment of

those control objectives requires an engine management

system (EMS) simultaneously coordinating multiple actuators

[7], [8]. In [7], an engine control unit (ECU) is calibrated

based on software-in-the-loop simulation of a GT-Power

model for a diesel engine with common-rail injection system,

EGR and a 2-stage boosting system. In [8], control parameters

in an EMS such as air mass flow rate, injection timing and rail

pressure are calibrated for a diesel engine fueled with

biodiesel blend.

The common-rail (CR) fuel injection system enables

simultaneous control of the rail pressure, injection timing and

injection pulse width (IPW) [4]. As a result, the injected fuel

amount is precisely metered and the combustion phasing can

be optimized [1], [3], [6]. In [1], the effect of fuel injection

timing on the combustion heat release process and the

emissions is experimentally studied on a diesel engine with

both in-cylinder diesel fuel injection and premixed DME port

injection. In [3], a single cylinder diesel engine is used to

study the effect of fuel injection timing and rail pressure on

the heat release phasing, emissions and performance output. In

[6], a multiple injection strategy is applied in a closed-loop

control structure to achieve desired cylinder pressure traces. In

order to supply the engine with precise amount of fuel and to

provide proper air-fuel mixture demanded at various speed

and load conditions, accurate and fast rail pressure regulation

becomes necessary [5], [9]. In [5], a nonlinear model for a

common-rail injection system is developed and based on

which a sliding model control strategy is proposed for the rail

pressure regulation. Both the model and the control strategy

are validated by a virtual detailed simulation environment in

[5]. In [9], a control structure with a static feedforward and an

integral feedback action is used for regulation of rail pressure

in a gasoline direct injection (GDI) engine. The experimental

results show that the designed controller is able to keep the rail

pressure oscillation within 10 bar [9].

In an effort to achieve optimal control of the combustion

process of a common-rail diesel engine, an engine

management system (EMS) is built in this study based on the

MOTOTRON rapid prototyping system. Real-time calculation

of the combustion heat release rate (HRR) is conducted based

on the cylinder pressure measurement. To facilitate the control

development of the common-rail fuel injection system, a test

platform without the cylinders is built. Results show that

precise control of the rail pressure and injection timing is

achieved. As a result, the injected fuel amount and combustion

phasing are regulated by the EMS. Actuation of the exhaust

gas recirculation (EGR) valve also results in reduced NOx

emission.

In Sec. II, the diesel engine system and the common-rail

fuel injection system test bench are introduced. In Sec. III, the

EMS for the common-rail diesel engine is developed. In Sec.

IV, results from the fuel injection test bench and the diesel

engine are displayed. Real-time calculation of the heat release

process shows that the combustion phasing is precisely

controlled by the EMS.

II. EXPERIMENTAL SETUP

The EMS is developed based on a Mitsubishi 4M42-4AT2

commercial truck diesel engine with 2977 c.c. displaced

volume and rated power 95 kW at 3200 rpm. Fig. 1 shows the

experimental engine equipped with turbo charger, common-

rail direct-injection system and EGR system. The diesel

engine is connected to a SCHENCK MP-DYNAS 335

alternative current motor dynamometer, which absorbs a

maximum power of 335 kW within 8000 rpm. The EMS is

developed based on the MOTOTRON rapid prototyping

system with measurement of the intake flow rate, temperature

and pressure in the intake, exhaust runners and the fuel rail,

cylinder pressure, engine speed and engine coolant

temperature (ECT). Base on the EMS, control system for the

CR fuel injection system and EGR system is developed.

Specifically, a MPROP valve is used to regulate the CRP

which combined with the IPW determines the injected fuel

amount. The real-time calculation of combustion process is

conducted based on the XPC target platform with

measurement from an AVL GH13P cylinder pressure sensor

and a crankshaft encoder. The engine-out NOx emission is

measured by a NGK/Continental Smart NOx Sensor (SNS)

with measurement range from 0 ppm to 3012 ppm.

Fig. 1. The diesel engine control system and the real-time combustion

analysis system.

To facilitate the control development and calibration of the

common-rail injection system, a CR test bench as shown in

Fig. 2 is built in this study. The BOSCH CP3.3 CR pump is

driven by an induction motor, instead of the engine. The CRP

is regulated by controlling the duty cycle of a PWM signal fed

to the MPROP valve. The motor is connected to a 60 minus 2

crank type wheel and a X plus 1 type cam wheel (the same

wheels used on the diesel engine). The wheel system is again

driven by the MOTOTRON engine control module (ECM).

Fig. 2. Common-rail test bench.

III. EMS DEVELOPMENT

Fig. 3 shows the block diagram of the diesel engine control

system. The subsystems of the diesel engine contain the

common-rail, injectors and the EGR system. Performance

variables include the engine output torque and NOx emission.

Control decisions of the EMS are made based on the engine

speed (RPM), accelerator pedal position (APP), ECT and CRP.

Specifically, the EMS regulates the CRP by controlling the

duty cycle of PWM signal to a MPROP valve. The start of

injection (SOI) controls the injection timing while the IPW,

combined with the CRP, determines the injected fuel amount.

The EGR, on the other hand, needs to be carefully used to

reduce the NOx emission at the expense of performance

deterioration.

Fig. 3. Block diagram of the diesel engine control system.

A. CR Pressure Controller

The level of CRP is controlled by the opening rate of an

intake fuel regulation valve (MPROP) on the high pressure

pump. The MPROP is a normal open type solenoid value

which can be actuated with Pulse Width Modulation (PWM)

signal. Fig. 4 shows the feedforward plus feedback control

structure for regulation of the CRP with engine test. The CRP

set points need to be calibrated at various operating conditions,

similar to the experimental results show in Fig. 11. The

feedforward controller can be as simple as a look-up table

which can be calibrated based on the common-rail test bench

results in Sec. IV. The feedback part is a PID controller and

the control gains are again determined based on the

experimental results on the test bench in Sec. IV.

Fig. 4. Structure of the common-rail pressure controller.

B. Fuel Injector Controller

The combustion timing and heat release rate controller of

the common-rail diesel engine can be controlled by the SOI

timing and IPW of injector, respectively. Fig. 5 shows the

structure of the injector control system. The inputs to this

system include the engine speed, ECT and APP.

Fig. 5. Structure of the fuel injector controller.

In determining the injection timing and injected fuel amount,

a fuel manager block in Fig. 6 is first constructed based on the

estimation of indicated mean effective pressure (IMEP), which

is a better indication of a particular engine’s ability to do work

than the output torque. The MEP can be obtained by dividing

the work per cycle by the cylinder volume displaced per cycle

or expressed in terms of torque as in (1).

d

R

V

TnMEP

2 (1)

where Rn is the number of crank revolutions for each power

stroke per cylinder (two for four-stroke cycles) and T is the

engine torque [2]. The IMEP can thus be derived by summing

up the brake mean effective pressure (BMEP) and friction

mean effective pressure (FMEP), which can be obtained by

substituting the brake torque bT and friction torque fT into (1)

respectively. Based on the IMEP signal, linear interpolation is

used to obtain the required fuel mass per cycle. The required

fuel volume per cycle can then be derived by dividing the fuel

mass with the fuel density D, which is calibrated as a function

of fuel temperature.

With the required fuel volume and IMEP derived and the

measurement of engine speed and CRP measured, two lookup

tables are used to obtain the SOI and IPW signals. Those two

look-up tables again need to be calibrated based on the

experimental results in Sec. IV using the CR test bench and

the diesel engine.

Fig. 6. Structure of the fuel manager.

C. EGR Controller

EGR is an effective strategy used to reduce NOx emission

by mainly decreasing the peak temperature in the cylinder. Fig.

7 shows the feedforward structure of the EGR control system.

With the measurement of engine speed (RPM) and APP, set

points for EGR valve opening rate are determined. The EGR

valve motor is then driven by the duty cycle of the PWM

signal.

Fig. 7. Structure of EGR controller.

IV. EXPERIMENTAL RESULTS

In this section, experiments are conducted on both the CR

test bench and the diesel engine for calibration of the

controllers developed in Sec. III. Results of real-time

calculation of the combustion heat release rate (HRR) are then

used to examine the effects of injection timing based on

cylinder pressure measurement.

A. CR Test Bench Results

The level of CRP is controlled by the PWM duty cycle of

the MPROP valve in the high pressure pump. Experiments are

conducted on the CR platform to obtain the relations between

the CRP and PWM duty cycle of the MPROP valve as shown

in Fig. 8, which is used to calibrate the feedforward map in

Fig. 4. Since the MPROP is a normal open valve, longer PWM

duty cycle results in less fuel flow through the valve and thus

drops the fuel pressure in the common rail. For this specific

common-rail system, the rated rail pressure is 1600 bar. Fig. 9

shows the injected fuel volumes at various rail pressures and

IPW, which is used for calibration of the IPW map shown in

Fig. 5. Higher rail pressure or longer IPW generally result in

more fuel injected. Fig. 10 shows the control results of the rail

pressure during a large APP step change from 0% to 80% at

1000 rpm. The results show that the rising time is less than 2

second and the steady state error is less than 5% in tracking

the desired rail pressure.

B. Diesel Engine Test Results

Fig. 11 shows the settings of the desired rail pressure at

various engine operating conditions, which is necessary for the

calibration of the fuel pressure map in Fig. 4. The rail pressure

needs to be raised at higher engine speed so as to increase the

injection rate. Similarly, the rail pressure also needs to be

raised at higher APP or higher torque demand as more fuel is

required. Fig. 12 on the other hand shows the FMEP

associated with RPM and ECT in the fuel manager block

shown in Fig. 6. FMEP is increased with the rising of the

engine speed, but decreased with the rising of the ECT.

The start of combustion (SOC) timing, which is critical to

the engine performance, is closely related to the start of

injection (SOI) timing. Thus effective control SOI is key to the

improved power output and reduced fuel consumption. Fig. 13

shows the effect of start-of-injection timing on the diesel

engine brake power at various engine operating points. The

tests contain 9 operating points at various speeds and engine

loads. Fig. 13 shows that more advanced injection timing is in

general required at higher engine speed so as to generate the

maximum brake power at each operating condition. The best

injection timing that generates maximum brake power is

marked with circle at each operating condition in Fig. 13.

Non-optimized injeciton timings may result in incomplete

combustion causing poor engine power output and increased

fuel consumption.

Fig. 8. MPROP valve PWM map.

Fig. 9. Injected fuel volumes at various rail pressures and injection pulse

widths (IPWs).

C. Real-Time Calculation of HRR

1) HRR calculation: The heat release phasing is critical to

the brake power output of a internal combustion engine. For

real-time calculation of the HRR, a simple heat release rate

model is derived based on the conservation of energy and

ideal gas law.

dt

dPV

dt

dVP

dt

dQhr

1

1

1

(2)

where hrQ is the released energy, is the specific heat ratio,

and P and V are the cylinder pressure and volume respectively.

The xPC target platform with cylinder pressure sensors and a

crankshaft encoder is used for realization of the real-time HRR

calculation based on (2).

Fig. 14 and Fig. 15 show the cylinder pressure measurement

with various start-of-injection (SOI) timings around 1500 rpm

and 75% load condition, where TDC represents the top dead

center. Higher peak pressure is observed at a more advanced

SOI timing. Based on the results in Fig. 13, however, the

higher peak pressure does not necessarily lead to higher brake

power output. Fig. 16 shows the heat release rate (HRR)

calculated based on (2) at the same operating conditions.

Ignition delay, which is defined as the interval between the

SOI and start of combustion (SOC), is observed in Fig. 16 and

will be further discussed in the next section. After the ignition

delay period, a two-phase combustion is observed [2]. The

first HRR peak corresponds to the premixed combustion phase

characterized with rapid heat release from combustion of the

fuel which has mixed with air to within the flammability limits

during the ignition delay period. After that, the heat release

rate is controlled by the rate at which fuel-air mixture becomes

available for burning. Fig. 16 shows that an advanced SOI

results in higher HRR peak in the premixed stage but lower

peak in the mixing-controlled stage. The maximum brake

power is achieved when the second HRR peak (mixing-

controlled phase) occurs around 5° ATDC (as the piston just

moves past the top dead center).

Fig. 10. Closed-loop response of the rail pressure during a large APP step

change from 0% to 80% at 1000 rpm.

Fig. 11. Look-up table for the desired rail pressure.

Fig. 12. Look-up table for the FMEP.

Fig. 13. Effect of start-of-injection (SOI) timing on diesel engine brake power

at various engine operating points.

2) Ignition delay: Results in the previous section infer

that the ignition delay plays an important role in controlling

the two combustion phases. Fig. 17 shows the ignition delay

and the magnitude of the 1st

and 2nd

HRR peaks at various

injection timings. The non-monotonic trend results from the

fact that the ignition delay is quite sensitive to the temperature

and pressure which change significantly close to TDC [2].

Specifically, if the SOI is advanced, the initial temperature and

pressure are lower and thus result in longer ignition delay. On

the other hand, if the SOI is closer to TDC, the temperature

and pressure are initially slightly higher but then decrease as

the delay proceeds and thus may also lead to longer delay. Fig.

17 also reveals that the magnitude of the first HRR peak

correlates well with the ignition delay. Longer ignition delay

allows better mixing of fuel and air in the initiation of the

auto-ignition, thus results in a higher first HRR peak. As more

fuel is consumed in the premixed phase, less heat is released

in the mixing-controlled phase as evident by the lower 2nd

HRR peak at -25° ATDC SOI.

Fig. 14. Cylinder pressure of the diesel engine with various start-of-injection

(SOI) timings around 1500 rpm and 75% load.

Fig. 15. Zoomed view of Fig. 14.

D. EGR Setting for Engine-out NOx Reduction

EGR is a commonly used strategy that reduces engine-out

NOx emission at the cost of deteriorated engine performance.

The recirculated burned gas increases the heat capacity of the

cylinder charge and thus reduces the flame temperature

leading to reduced NOx emission. Fig. 18 shows the results of

engine out NOx emission with various EGR settings when the

SOI is fixed at the best timing around each operating condition.

The NOx emission is significantly reduced when more EGR is

used at 1500 rpm and 2000 rpm. On the other hand, the NOx

emission at 2500 rpm is only slightly reduced when more

EGR is used as the actual EGR flow rate is limited by the

boosted intake pressure at higher engine speed.

V. CONCLUSIONS

In this paper, an EMS for a turbo-charged common-rail

diesel engine with EGR is developed and calibrated based on

experimental data from a common-rail test bench and the

diesel engine. Experimental results show that the heat release

process can be precisely controlled by the injection timing.

Maximum brake torque is achieved at the right combustion

phasing (2nd

HRR peak around 5° ATDC). The more advanced

injection timing is in general required at higher engine speed

so as to generate the maximum brake power at each operating

condition. By controlling the injection timing, injection pulse

width, rail pressure and EGR properly, optimal performance

and reduced engine-out NOx emission can be achieved.

Fig. 16. Heat release rate of the diesel engine with various start-of-injection

(SOI) timing around 1500 rpm and 75% load.

Fig. 17. Effect of start-of-injection (SOI) timing on diesel engine ignition

delay and the 1st and 2nd HRR peaks around 1500 rpm and 75% load.

Fig. 18. Engine-out NOx emissions with various operation conditions and

EGR settings.

In the future, the developed EMS can be used for closed-loop

combustion control with cylinder pressure feedback.

ACKNOWLEDGMENT

The authors would like to thank the funding support from

Bureau of Energy, Ministry of Economic Affairs, Taiwan,

R.O.C.

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