experimental investigation of combustion, performance and emission ...

C Kannan et. al. / International Journal of Engineering Science and Technology Vol. 2(8), 2010, 3525-3534

EXPERIMENTAL INVESTIGATION OF COMBUSTION, PERFORMANCE AND EMISSION CHARACTERISTICS OF DI DIESEL ENGINE UNDER HCCI MODE WITH POROUS MEDIUM COMBUSTION C KANNAN * Department of Automobile Engineering, Sri Venkateswara College of Engineering, Post Bag No.3, Pennalur, Sriperumbudur, Tamilnadu – 602 105, India

P TAMILPORAI Division of IC Engines, Department of Mechanical Engineering, College of Engineering, Guindy Anna University, Chennai, Tamilnadu- 602 105, India

Abstract: In recent times, homogeneous combustion has been a proven technology to attain high efficient and low emission engines. Homogenous Charge Compression Ignition (HCCI) engines are able to have efficiencies as high as Compression Ignition, Direct Injection (CIDI) engines, while producing ultra-low emissions of nitrogen oxides (NOx) and particulate matter (PM).HCCI combustion is achieved by controlling the temperature, pressure and composition of the fuel-air mixture so that it spontaneously gets ignited in the combustion chamber. Numerous techniques such as Variable Exhaust Gas Recirculation (VEGR), Variable Compression Ratio (VCR) and Variable Valve Timing (VVT) have been proposed to control the homogeneous combustion inside the engine cylinder. Even though these techniques are attractive and having good time response, they are too expensive to afford. This paper investigates the performance, combustion and emission characteristics of a Direct Injection (DI) diesel engine under HCCI mode which is established through an effective and affordable technique called Porous Medium Combustion (PMC). Keywords: homogeneous combustion; porous medium combustion; particulate matter; nitrogen oxides. 1. Introduction Reduction in diesel engine emissions, in particular NOx and PM emission is becoming as high priority issue as emission norms are getting more and more stringent now a days. The rigid emission standards urged the engine researchers to innovate techniques that produce high efficient and low emission engines. One such novel technique is HCCI combustion. Moreover, this technique can be scaled to virtually every size-class of transportation engines from small motorcycle to large ship engines [U.S congress report, (2001)]. The operational control of an HCCI engine over a wide range of speeds and loads is probably the most difficult hurdle. HCCI engine ignition is largely determined by the charge mixture composition, its time-temperature history and to a lesser extent pressure. Although it has been demonstrated that HCCI engines operate well at low to medium loads, severe complications have been observed at high loads. At higher loads, the combustion becomes more rapid which subsequently leading to intense mechanical noise, engine damage and unacceptable levels of NOx emissions. Preliminary research indicates that the operating range of HCCI engines can be extended significantly by partially stratifying the fuel-air charge/ residual charge at high loads. The potential mechanisms for achieving partial charge stratification include: in-cylinder fuel injection, water injection, varying the intake and in-cylinder mixing processes and altering in-cylinder flows to vary heat transfer. Due to the difficulties being faced at higher loads, HCCI engines are generally designed to switch over to conventional Spark Ignition (SI) or Compression Ignition (CI) mode of combustion at this operational region [Weclas (2004a)].

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C Kannan et. al. / International Journal of Engineering Science and Technology Vol. 2(8), 2010, 3525-3534 An experimental technique which inherits the positive aspects of HCCI combustion at low to medium loads and concurrently keeps away from the negative attributes of HCCI combustion at higher loads is the matter of immediate concern. Based on literature survey [Chidambaram (2009) and Weclas (2004b)], homogeneous combustion established through porous medium combustion technique (HCCI-PMC) has been attempted in this experimental investigation. In this study, PMC technique has been implemented on a single cylinder, direct injection diesel engine. It has been found that this technique is able to produce relatively high efficiency and low particulate emissions from a diesel engine. Low NOx emission than HCCI mode is the added advantage of this technique [Jan (2001), Wang (2000) and Afsharvahid (2007)]. In the initial stage, the conventional engine was operated without any modifications. In the second stage, the engine was made to run in HCCI mode, established through the combination of technologies such as high pressure fuel injection, injection timing advance, pre-heating the air of induction manifold and cooled exhaust gas recirculation. The performance, combustion and emission characteristics of the engine under this mode were recorded. In the third stage, a ceramic material with large porosity was introduced into the combustion chamber of the engine to accomplish HCCI-PMC. Then the experiments were conducted and the readings were taken. As an end note, the combustion, performance and emission characteristics of engine under different modes of combustion such as Conventional, HCCI and HCCI-PMC were compared and presented in this paper. 2. Experimental Setup Generally, the porous medium combustion can be achieved by the precise placement of porous ceramic material in either of the following locations: cylinder, engine head or piston. In this research work, the porous ceramic material was placed on the top of piston cavity and had been detained in its position through an appropriate locking mechanism. The inherent physical and thermal characteristics of porous ceramic material was utilized for the fast and complete evaporation of the liquid fuel while large porosity characteristic being utilized for proper mixing with air and volumetric combustion. The photographic view of such a piston with porous medium implementation was shown in Fig. 1.The chemical composition and mechanical properties of porous ceramic material were given in Table 1.

Fig. 1.Photographic view of piston with porous medium implementation Table 1. Properties of porous ceramic material

Molecular formula ZrO2

Density (g/m3) 5.89

Solubility in water Negligible

Melting point (0 C) 2715

Boiling point (0 C) 4300

A single cylinder four stroke direct injection air-cooled diesel engine, most commonly used for agricultural applications in India, was used for the experimental investigation. The specifications of this engine were given in Table 2. The schematic diagram of the experimental set-up was shown in Fig. 2. The engine was coupled to an electrical dynamometer to provide the brake load. The fuel consumption was measured with the aid of a glass burette and stopwatch on volume basis. A Piezo-electric pressure transducer (GH12D Miniature Pressure Transducer) coupled with an angle encoder was used to measure the combustion chamber pressure with respect to crank angle. The setup was connected to a personal computer with AVL engine evaluation software. Five-gas

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C Kannan et. al. / International Journal of Engineering Science and Technology Vol. 2(8), 2010, 3525-3534 exhaust analyzer was used to determine the emissions of CO (carbon monoxide), CO2 (carbon dioxide), HC (hydrocarbon) by infra-red measurement and NOx (nitrogen oxides) by electrochemical sensors. Smoke intensity was measured with an AVL 415 smoke meter. Table 2 Specifications of experimental engine

Make Model Bore × Stroke (mm) Compression ratio Cubic capacity Rated power

Kirloskar TAF 1 87.5 × 110 17.5:1 0.661 litres 4.4 KW Table 2 (Continued)

Rated speed Start of injection Connecting rod length Injector operating pressure

1500 rpm 23.4º bTDC 220 mm 200 – 205 bar

5

16

4 6 15

13 17

10

8

11

9

12

7

3

14

1 2

1 - Diesel engine 4 – Air box 7 – Fuel measurement 10 – Charge amplifier 13 – Computer 16 – Air preheater

2 - Electrical dynamometer 5 – U-tube manometer 8 – Pressure transducer 11 – TDC amplifier circuit 14 – Exhaust gas analyzer 17 – EGR control valve

3 – Dynamometer controls 6 – Fuel tank 9 – TDC position sensor 12 – Analog to digital card 15 – AVL smoke meter

Fig. 2. Schematic layout of experimental set-up

3. Results and Discussion In this research work, an attempt has been performed to compare the combustion and performance characteristics of a DI diesel engine under conventional, HCCI and HCCI-PMC modes of combustion. 3.1. Combustion characteristics 3.1.1. Ignition delay The variation of ignition delay with brake power for different modes of combustion was shown in Fig. 3. It was inferred that ignition delay started to decrease with an increase in brake power for almost all modes of combustion. With an increase in brake power, the amount of fuel being burnt inside the cylinder gets increased and subsequently

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C Kannan et. al. / International Journal of Engineering Science and Technology Vol. 2(8), 2010, 3525-3534 the temperature of in- cylinder gases gets increased. This may lead to reduced ignition delay in all modes of combustion. However, the ignition delay for diesel fuel was lower under HCCI and HCCI-PMC modes than the conventional combustion mode. It was evident that the ignition delay was lowest in HCCI-PMC mode from medium to high load. This might be due to the positive influence of hot porous medium on the evaporation of liquid fuel and it’s mixing with air.

17

Ignition delay in deg CA

16.5 16 15.5 15 14.5

Conventional HCCI

14

HCCI-PMC

13.5 0

1.1

2.2 Brake power in kW

3.3

4.4

Fig. 3. Variation of ignition delay for different modes of combustion

3.1.2. Peak pressure The variations of peak cylinder gas pressure with brake power for different modes of combustion were given in Fig. 4. It was observed that the peak pressure gets increased with an increase in brake power. During measurements, the maximum peak pressure under HCCI mode and lowest peak pressure under conventional combustion mode were observed. In a conventional direct injection diesel engine, at any point of time, only a fraction of total injected fuel was getting burnt. But on the other hand, under HCCI combustion mode, the entire fuel-air mixture got ignited and also burnt simultaneously (volumetric combustion). This might be leading to highest peak pressure in HCCI mode. However, in HCCI-PMC mode, the magnitude of peak pressure was slightly lower than HCCI, which might be due to pressure drop across the pores of ceramic medium placed inside the combustion chamber.

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73 71

Peak pressure in bar

69 67 65 63 61 59 Conventional HCCI HCCI-PMC

57 55 53 0

1.1

2.2 Brake Power in kW

3.3

4.4

Fig. 4. Variation in peak pressure for different modes of combustion

3.1.2. Heat release rate The heat release rate at different crank angles at rated load for different modes of combustion was shown in Fig. 5.It was inferred that the heat release patterns of all combustion modes were similar but with slight variations. It was observed that the heat release pattern was rapid and intense in HCCI mode combustion. In HCCI-PMC mode, even though the heat release rate was more rapid than the conventional combustion mode; the heat was released in a controlled manner.

Rate of heat release in J/ deg CA

90 80

Conventional HCCI

70

HCCI-PMC

60 50 40 30 20 10 0 -10 -12

-10

-8

-6

-4 -2 0 2 4 6 Crank angle in degrees (aTDC)

8

10

12

Fig. 5. Rate of heat release pattern for different modes of combustion

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C Kannan et. al. / International Journal of Engineering Science and Technology Vol. 2(8), 2010, 3525-3534 3.2. Performance Characteristics 3.2.1 Specific fuel consumption

Specific fuel consumption in g/kW-hr

0.6 0.5 0.4 0.3 0.2 Conventional HCCI HCCI-PMC

0.1 0 0.0

1.1


3.3

4.4

Fig. 6. Comparison of specific fuel consumption for different modes of combustion

The variation in specific fuel consumption against brake power for different modes of combustion was shown in Fig. 6. It was inferred that the specific fuel consumption was lower in the case of HCCI and HCCI-PMC, as these modes were predominately operated with a dilute homogeneous charge. Even within these two modes, HCCI-PMC had superior characteristics over HCCI mode, which might be due to enhanced evaporation and mixing of fuel with air by the presence of hot porous medium. 3.2.2 Brake thermal efficiency From Fig 7, it was inferred that the brake thermal efficiencies were increasing with an increase in brake power for all modes of combustion that were under consideration. Even though the brake thermal efficiencies did not vary too much between HCCI and HCCI-PMC modes, these modes were found to offer better thermal efficiencies than the conventional combustion mode. This might be due to the enhanced evaporation and mixing rate in the case of HCCI-PMC mode of combustion.

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Brake thermal efficiency in %

30 25 20 15 10 Conventional HCCI HCCI-PMC

5 0 0.0

1.1


3.3

4.4

Fig. 7. Comparison of brake thermal efficiency for different modes of combustion

3.3. Emission Characteristics

3.3.1 Unburned hydrocarbons (UBHC)

Unburned hydrocarbons in ppm

30

Conventional HCCI HCCI-PMC

25 20 15 10 5 0 0.0

1.1

2.2

3.3

4.4

Brake power in kW Fig. 8. Comparison of hydrocarbon emissions for different modes of combustion

The comparison of unburned hydrocarbon emissions in a DI diesel engine with different modes of combustion was presented in Fig. 8. HC emissions were significantly higher for HCCI and HCCI-PMC modes. Since HCCI operates on lean mixtures, the peak temperatures were lower in comparison to a conventional diesel engine. These low peak temperatures might be leading to incomplete burning of fuel, especially near the walls of the combustion chamber, which was one of the possible reasons for higher HC emissions in these modes. However HC emissions were lower in HCCI-PMC over HCCI mode. This might be due to later stage oxidation of HC compounds inside the hot porous medium.

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C Kannan et. al. / International Journal of Engineering Science and Technology Vol. 2(8), 2010, 3525-3534 3.3.2 Carbon monoxide (CO)

Conventional HCCI HCCI-PMC

Carbon monoxide in %

0.25

0.2

0.15

0.1

0.05

0 0.0

1.1

2.2

3.3

4.4

Brake power in kW

Fig. 9. Comparison of carbon monoxide emissions for different modes of combustion

The comparison of carbon monoxide emissions in a DI diesel engine with different modes of combustion was presented in Fig. 9. Carbon monoxide emissions were also higher for HCCI and HCCI-PMC modes. However, carbon monoxide emissions were lower in HCCI-PMC mode than HCCI mode under low to medium loads. Surplus oxygen availability and the presence of hot porous medium might promote later stage oxidation of carbon monoxide across the combustion chamber, which consequently resulted in lower emissions at these loads. 3.3.3 Nitrogen oxides (NOx) As far as the nitrogen oxide emissions were concerned, it was found to be the lowest in the case of HCCIPMC mode. This might be due to the heat absorbing characteristics of porous medium which was placed inside the combustion chamber. Due to this heat absorption from the reaction zone, the in-cylinder temperature was comparatively lower in HCCI-PMC mode through out the cycle. This consequently resulted in low thermal NOx emissions. In HCCI mode of combustion, at higher loads, the combustion became more rapid and intense and eventually producing unacceptable levels of NOx emissions. This was shown in Fig. 10.

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1350

Nitrogen oxides in ppm

1150

950

750

550

Conventional HCCI

350

HCCI-PMC 150 0.0

1.1


3.3

4.4

Fig. 10. Comparison of nitrogen oxide emissions for different modes of combustion

3.3.4 Soot

250 Conventional HCCI

200 Soot in mg/m

3

HCCI-PMC

150

100

50

0 0.0

1.1


3.3

4.4

Fig. 11. Comparison of soot emissions for different modes of combustion

Due to diluted homogeneous charge in HCCI and HCCI-PMC modes, the soot emissions were found to be lower in these modes than the conventional mode of combustion. This was presented in Fig. 11. In HCCI-PMC mode, the soot emission was higher at low range of part loads due to ineffective evaporation of injected fuel. But under medium to higher loads in HCCI-PMC mode, the porous medium absorbed heat (from the reaction zone of the combustion chamber) was utilized for the effective evaporation of liquid fuel and its porosity distribution assisted in thorough mixing of fuel vapour with air, eventually leading to homogenous mixture which in turn resulted in lowest soot emission of all modes.

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C Kannan et. al. / International Journal of Engineering Science and Technology Vol. 2(8), 2010, 3525-3534 4. Concluding Remarks

The combustion, performance and emission characteristics of single cylinder DI diesel engine under conventional, HCCI and HCCI-PMC modes were investigated and summary of the findings were given below. (1) The ignition delay was found to be lower in HCCI and HCCI-PMC modes due to homogeneous mixture conditions. (2) Maximum peak gas pressure was observed in HCCI mode; whilst slightly lower peak pressure than HCCI mode was observed in HCCI-PMC mode due to pressure drop across the porous ceramic medium which was placed in the combustion chamber. (3) The brake thermal efficiencies were higher in HCCI and HCCI-PMC modes than the conventional combustion mode. (4) Soot emission under HCCI and HCCI-PMC modes were found to be superior to conventional mode of combustion. (5) The NOx emissions were comparable with conventional mode under low to medium loads. But at high load under HCCI mode, the NOx emission was higher due to rapid combustion established through homogeneous mixture. However, due to heat absorption characteristics of porous medium, the NOx emission was lower in HCCI-PMC mode when compared to HCCI mode. (6) HCCI and HCCI-PMC modes had inferior characteristics with respect to HC and CO emissions. But it could be easily resolved by the use of ultra low light-off temperature oxidation catalysts. As an end note, this research work would like to conclude that with proper implementations, the HCCI-PMC mode had the potential of offering better combustion, performance and emission characteristics in direct injection diesel engines. Acknowledgement

We thank the management of Sri Venkateswara College of Engineering for providing us the necessary experimental setup to perform this research work. References [1] [2] [3] [4] [5] [6] [7]

Afsharvahid.S., Ashman.P.J., Dally.B.B.,(2007): Investigation of NOx conversion characteristics in a porous medium, Combustion and Flame, 06, pp.1-12 Kannan Chidambaram, Tamilporai Packirisamy(2009): Smart ceramic materials for homogeneous combustion in internal combustion engines – A review, Thermal Science,13 , pp. 153-163 Miroslaw Weclas(2004): Potential of porous medium combustion technology as applied to internal combustion engines, Sonderdrunck Schriffenreihe Der Georg- Simon -Ohm – Fachhochschule Numberg NR.32, ISSN 1616-0762 Miroslaw Weclas (2004): Strategy for intelligent internal combustion engine with homogeneous combustion in cylinder, Sonderdrunck Schriffenreihe Der Georg- Simon -Ohm – Fachhochschule Numberg NR.32, ISSN 1616-0762 Macek Jan, Polasek Milos (2001): Porous medium combustion in engines may contribute to lower NOx emissions, Joesef Bozek Research Center, Czech Technical University in Prague, Czech Republic, Paper Code: F02V147 U.S Department of Energy, A Report to US Congress (2001):Homogeneous Charge Compression Ignition (HCCI) Technology Wang.W.G., Lyons.D.W., Clark.N.N.,Gautam.M (2000): Emissions from nine heavy trucks fueled by diesel and biodiesel blend without engine modification, Environmental Science Technology, 34, pp.933-939

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