Sensitivity of combustion noise and NOx and soot emissions to pilot injection in PCCI Diesel engines

doi:10.1016/j.apenergy.2012.11.040

Applied Energy

Volume 104, April 2013, Pages 149-157

https://doi.org/10.1016/j.apenergy.2012.11.040 Get rights and content

Abstract

New combustion concepts have been recently developed with the purpose to tackle the problem of the high emission levels of traditional direct injection Diesel engines. A good example is the premixed charge compression ignition (PCCI) combustion, a strategy in which early injections are used, causing a burning process in which more fuel is burned in premixed conditions, which affects combustion noise. The use of a pilot injection has become an effective tool for reducing combustion noise. The main objective of this paper is to analyze experimentally the pollutant emissions, combustion noise, and performance of a Diesel engine operating under PCCI combustion with the use of a pilot injection. In addition, a novel methodology, based on the decomposition of the in-cylinder pressure signal, was used for combustion noise analysis. The results show that while the PCCI combustion has potential to reduce significantly the NO_x and soot emission levels, compared to conventional Diesel combustion strategy, combustion noise continues to be a critical issue for the implementation of this new combustion concept in passenger cars.

Highlights

► PCCI combustion with two injections reduces NO_x and soot but affects engine torque. ► PCCI combustion noise level and quality depend on the pilot injection. ► Combustion noise must be improved before PCCI becomes a suitable alternative.

Introduction

In recent years, direct injection (DI) Diesel engines have become the most often used propulsion system in automotive vehicles in Europe. Nevertheless, Diesel engines are not exempt from certain problems, including high nitrogen oxides (NO_x) and soot emissions, the high levels of noise produced, and the consumption of large quantities of oil-derived fuels. Regarding this last aspect, the use of new bio-fuels appears to be a feasible alternative for alleviating the dependence on conventional fuels [1].

The noise produced by Diesel engines is currently receiving more and more attention, due to the discomfort that it causes on both passengers and pedestrians [2]. Combustion noise is noteworthy for being the main source of noise in vehicles equipped with Diesel engines. This noise is generated by the interaction of pressure and mechanicals forces. During the combustion process, a sudden pressure rise is produced which induces engine block vibration and the subsequent noise emission [3], [4]. Combustion noise mainly depends on the combustion chamber design, the fuel injection system, the in-cylinder temperatures, and the engine compression ratio [5]. This noise can be controlled by the application of both passive and active actions. A typical passive action is engine encapsulation, whereas engine hardware and engine operating conditions settings are among the active actions available for combustion optimization [6]. The geometry of the bowl plays an important role in engine noise control due to its influence on the development of resonant pressure fluctuations, which are induced by the ignition characteristics [7], [8]. Nevertheless, depending on the strategy employed the use of active controls can have a negative impact on engine performance, driveability and pollutant emissions.

To overcome the problems of Diesel engines regarding pollutant emissions, several advanced combustion concepts have been proposed. One of the most relevant combustion concepts is that of premixed charge compression ignition (PCCI) combustion. The PCCI combustion concept is well known for its ability to improve performance while reducing both NO_x and soot levels. Unlike the conventional Diesel combustion, PCCI combustion uses early injections and relatively higher exhaust gas recirculation (EGR) rates for simultaneously reducing NO_x and soot emissions levels. However, many problems such as mixture preparation and control of the combustion phasing [9], together with knock, can damage the engine and generate annoying noise [10]. These characteristics complicate the application of this type of combustion. The use of a pilot injection has gained significant interest in recent years in conventional Diesel combustion as a means to reduce engine combustion noise [11]. Pilot injection reduces the ignition delay (ID) of the main injection and limits the amount of premixed combustion [12], [13].

The main objective of this paper is to analyze experimentally the pollutant emissions, combustion noise, and performance of a Diesel engine operating under PCCI combustion with the use of a pilot injection. For this purpose, a light-duty Diesel engine was adapted to operate under the PCCI combustion concept, taking into account the operating conditions in which this concept becomes more suitable for reducing NO_x and soot. A novel methodology based on the decomposition of the in-cylinder pressure signal was used to assess subjective and objective aspects of combustion noise [14], [15].

In the next section, the methodology used to perform the study is described. Then, the experimental set up and the diagnostic tools used are described in Section 3. Results for combustion noise, pollutant emissions, and performance are presented and discussed in Section 4. Finally, the main conclusions of this investigation are summarized in Section 5.

Section snippets

Methodology

The present study is mainly based on the use of a multi-cylinder Diesel engine at low load and medium speed (1500 rpm). The use of a pilot (or split) injection is one of the most promising solutions to reduce combustion noise and NO_x levels. It is for this reason that a fixed amount of 10 mg/stroke of fuel was injected in two injections for all the test cases. At the same time, and with the purpose of analyzing the effects of a pilot injection on PCCI combustion, different injection timings and

Experimental setup

A 1.6 l light-duty four-cylinder Euro IV turbocharged DI Diesel engine, equipped with a solenoid controlled and common rail injection system, was used. The main specifications of the engine and the injection system are given in Table 2. The engine was directly coupled to an asynchronous electric dynamometer, which allows control of the engine speed and load. The engine was installed in a fully equipped test cell, with all the auxiliary devices required for engine operation and control [23], [24]

Results and discussion

In the following paragraphs, results of engine pollutant emissions, performance, and combustion noise from PCCI combustion are presented and analyzed. Comparison is shown between the NO_x, soot, and brake mean effective pressure (bmep) and brake specific fuel consumption (bsfc) produced in PCCI conditions and those supplied by the engine operating in conventional Diesel combustion. Table 3 shows the relevant values for engine operation in conventional Diesel combustion.

Conclusions

Compared with conventional Diesel combustion, PCCI combustion with two injections (pilot and main) produced a significant reduction in emissions of NO_x (mostly due to the use of a high EGR rate) and soot (due to the increased levels of air and fuel premixing before SOC). Additionally, engine bmep was influenced by the pilot injection quantity. For these engine operating conditions, bmep decreased significantly as the pilot injection quantity increased above 40%.

From the acoustic point of view,

Acknowledgments

This work has been partially supported by Ministerio de Educacin y Ciencia through Grant No. TRA2006-13782. L.F. Mónico holds the Grant 2009/003 from Santiago Grisolía Program of Generalitat Valenciana.

References (32)

C.D. Rakopoulos et al.
Study of turbocharged diesel engine operation, pollutant emissions and combustion noise radiation during starting with bio-diesel or n-butanol diesel fuel blends
Appl Energy
(2011)
M. Jia et al.
The effect of injection timing and intake valve close timing on performance and emissions of diesel PCCI engine with a full engine cycle CFD simulation
Appl Energy
(2011)
A.J. Torregrosa et al.
Suitability analysis of advanced diesel combustion concepts for emissions and noise control
Energy
(2011)
S. Gan et al.
Homogeneous charge compression ignition (HCCI) combustion: implementation and effects on pollutants in direct injection diesel engines
Appl Energy
(2011)
D. Agarwal et al.
Effect of exhaust gas recirculation (EGR) on performance, emissions, deposits and durability of a constant speed compression ignition engine
Appl Energy
(2011)
F. Payri et al.
A complete 0D thermodynamic predictive model for direct injection diesel engines
Appl Energy
(2011)
E.G. Giakoumis et al.
Combustion noise radiation during the acceleration of a turbocharged diesel engine operating with biodiesel or n-butanol diesel fuel blends
Proc Inst Mech Eng, Part D – J Automob Eng
(2012)
Anderton D. Relation between combustion system and noise. SAE paper 790270;...
F. Payri et al.
New methodology for in-cylinder pressure analysis in direct injection diesel engines – application to combustion noise
Meas Sci Technol
(2005)
M. Graffarpour et al.
A numerical study of the use of pilot or split rate injection to reduce diesel engine noise
Proc Inst Mech Eng Part D – J Automob Eng
(2007)

Z. Win et al.

Investigation of diesel engine operating and injection system parameters for low noise, emissions, and fuel consumption using Taguchi methods

Proc Inst Mech Eng Part D – J Automob Eng

(2005)

A.J. Torregrosa et al.

Combustion chamber resonances in direct injection automotive diesel engines: a numerical approach

Int J Engine Res

(2004)

A. Broatch et al.

Computational study of the sensitivity to ignition characteristics of the resonance in DI diesel engine combustion chambers

Eng Comput

(2007)

J. Hou et al.

Characterization of knocking combustion in HCCI DME engine using wavelet packet transform

Appl Energy

(2009)

Graffarpour M, Baranescu R. NOx reduction using injection rate shaping and intercooling in diesel engines. SAE paper...

Yun H, sellnau M, Milovanovic N, Zuelch S. Development of premixed low-temperature Diesel combustion in a HSDI diesel...

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Sensitivity of combustion noise and NOx and soot emissions to pilot injection in PCCI Diesel engines

Abstract

Highlights

Introduction

Section snippets

Methodology

Experimental setup

Results and discussion

Conclusions

Acknowledgments

Appl Energy

Appl Energy

Energy

Appl Energy

Appl Energy

Appl Energy

Combustion noise radiation during the acceleration of a turbocharged diesel engine operating with biodiesel or n-butanol diesel fuel blends

Proc Inst Mech Eng, Part D – J Automob Eng

New methodology for in-cylinder pressure analysis in direct injection diesel engines – application to combustion noise

Meas Sci Technol

A numerical study of the use of pilot or split rate injection to reduce diesel engine noise

Proc Inst Mech Eng Part D – J Automob Eng

Investigation of diesel engine operating and injection system parameters for low noise, emissions, and fuel consumption using Taguchi methods

Proc Inst Mech Eng Part D – J Automob Eng

Combustion chamber resonances in direct injection automotive diesel engines: a numerical approach

Int J Engine Res

Computational study of the sensitivity to ignition characteristics of the resonance in DI diesel engine combustion chambers

Eng Comput

Characterization of knocking combustion in HCCI DME engine using wavelet packet transform

Appl Energy

Sensitivity of combustion noise and NO_x and soot emissions to pilot injection in PCCI Diesel engines