Optimization of the multi-carburant dose as an energy source for the application of the HCCI engine

Fuel 253 (2019) 15–24

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Full Length Article

Optimization of the multi-carburant dose as an energy source for the application of the HCCI engine ⁎

T

⁎

Hagar Alm ElDin Bastawissia, Medhat Elkelawya, , Hitesh Panchalb, , Kishor Kumar Sadasivunic a

Mechanical Power Engineering Department, Faculty of Engineering, Tanta University, Tanta, Egypt Government Engineering College Patan, Gujarat, India c Center for Advanced Materials, Qatar University, Qatar b

A R T I C LE I N FO

A B S T R A C T

Keywords: HCCI engine Alternative fuels Detailed chemical kinetics mechanism DME as a Biodiesel fuel CNG

The issue of utilizing multi-fuels for enhancing the burning process in the “Homogeneous charge compression ignition” HCCI engine cylinder has been developing significantly during the last decades. This technique has established to overcome the difficulties of the engine ignition and knock-like combustion control when distinguished with utilizing a single fuel during the engine management system. Furthermore, the developing concern towards the cleaner environment and the battle against wonderful weather by using the renewable fuel types are urgently required. In this research, the theoretical and experimental study will achieve the possibility of preparing a charged mixture, which consists of the air and three different kinds of alternative fuels. The prepared mixture was introducing into a mixing chamber near the intake manifold of the HCCI engine working at varying load conditions. Those fuels were the natural gas, hydrogen, and “Dimethyl ether” as a biodiesel fuel. The mixture has been utilizing to enhance the HCCI engine performance. However, the non-petroleum based alternative fuel such as “Dimethyl ether” DME has been used as an additive to the mixes of the natural gas or natural gas/hydrogen blends. Current methodology has been acquainting to make the chance of the engine ignition control is accessible, alongside its advantages to keeping away from the engine knocking or misfire operation. The ideal dose of each type of the tri-fuels composition with different percentages of each fuel used has been optimizing. Natural gas fuel is the primary fuel of the engine, and the other two types of fuel have used as additives for renewable fuels. The obtained results showed that there are certain proportions for each kind of the employed fuel in which the possibility of the engine operation without the occurrence of the knock-like combustion or the apparent of misfire operation have been achieving.

1. Introduction Recently the Homogeneous charge compression ignition (HCCI) is classified as advanced lean and low-temperature combustion technique for the application of the internal combustion engines due to its potential for high engine thermal efficiency and particularly low emissions of particulate and nitrogen oxides. HCCI has delegated another critical burning idea which is different than combustion procedure for spark ignition and diesel engine. This sort of the ignition approach hypothetically combines the advantages of the customary engines; low exhaust emission, and high thermal efficiency. The HCCI ignition techniques can utilize a variety of the available liquid or gaseous fuels with a little alteration in the original engine fuel system. In all cases, the ignition process in HCCI engine is begun by many auto-ignition spots to combust the entire in-cylinder lean and homogeneous fuel-air blend all

⁎

the while [1]. The comprehension of HCCI ignition idea is not restricted with common besides diesel and gasoline fuel only, but the extraordinary alternative fuel like biofuels, biodiesel, and hydrogen fuels can be utilized [2,3]. The further development and upgrade for the use of the alternative fuels inside the engine cylinder with the Homogeneous Charge Compression Ignition (HCCI) burning procedures accumulate the benefits of the standard Otto cycle with diesel engine rule. This strategy hypothetically joins the advantages of conventional engines; low crude discharges, and high mileage. In all cases, the ignition is continuing by the auto-ignition of the lean and homogeneous fuel-air blend [4]. Recently, concerning examinations with HCCI engines have been discernibly increasing. Along these lines, the HCCI engine fuel has mixed with the charged air, similar to the gasoline engine at higher air/ fuel proportion. This lean mixture will be ignited naturally because of

Corresponding authors. E-mail address: [email protected] (H. Panchal).

https://doi.org/10.1016/j.fuel.2019.04.167 Received 4 February 2019; Received in revised form 25 April 2019; Accepted 30 April 2019 Available online 10 May 2019 0016-2361/ © 2019 Elsevier Ltd. All rights reserved.

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Nomenclature

CIDI LTHR NTC IVC HRR CN w vc Pmotored S¯p vd Sx Bi δMk o mCNG m0DME m0Fuel

Abbreviations/Definitions/ TDC DME CNG ATDC BTDC HTHR SOI EVO CR PTFE mi h P T ON B N RPM m0Air m0H2 CA HCCI SI

Top dead center at the end of the compression stroke Dimethyl ether Compressed natural gas After a top dead center Before the top dead center High-temperature heat release Start of ignition Exhaust valve opening The compression ratio Polytetrafluoroethylene The number of moles of species The convective heat transfer coefficient Cylinder pressure Cylinder Temperature Octane number total regular error number of measurements Revolution per mints Airflow rate Hydrogen fuel flow rate Crank angle Homogeneous charge compression ignition Spark-ignition

Compression ignition direct injection Low-temperature heat release Negative temperature coefficient Inlet valve closing Heat release rate Cetane Number The average cylinder velocity gas The clearance volume The motored cylinder pressure The mean piston speed The displacement volume Arbitrary error present elemental systematic error Uncertainty in all obtained data Compressed natural gas flow rate DME flow rate fuel mass flow rate

Greek symbols Φ γ γswiral λTotal Λ ω̇ θk

Equivalence ratio Specific heat ratio The swirl velocity Total relative air/fuel ratio Relative air/fuel ratio Chemical production rate Sensitivity coefficient

no worry about the knock-like combustion which is the principal aim of the HCCI engine performance enhancement [16]. Also, the fundamental issues of utilizing CNG as a fuel in HCCI engines are the control objective of the auto-ignition timing over an extensive variety of rates and loads, constraining the heat released rate at high load operation, giving smooth operation through quick transient, accomplishing cold start, and meeting emission guidelines. Concerning CNG issues in an HCCI engine application, a critical research movement has been completed by including DME fuel into the natural gas blend [17–19]. The engine can work easily over various loads if a little parcel of the DME fuel is included into the CNG HCCI engine [20,21]. However, by finding the ideal measurement of the DME fuel as an added substance to the CNG fuel, the NOx outflow will be decreased in the case of lean air/fuel blend burning [22]. Furthermore, the best method may use to enhance and control the ignition practices of using CNG in HCCI engine was utilizing hydrogen added substances into the CNG/air blend. Likewise, other procedures proposed to conquer the snags concerning CNG in HCCI engines. In which, the exhaust gas fuel changing and Ozone added substances to the natural gas fuel can utilize additionally to enhance and develop the ignition zone of CNG/HCCI engines. This paper talks about the likelihood of using the alternative gaseous fuels in HCCI engine combustion, utilizing a tri-fuel operation technique. The issue of using alternative fuels such as CNG, Dimethyl ether, and hydrogen fuels for HCCI engines has developed during the last decades. This is not associated only with the diminishing petroleum product assets, as well as with the developing worry for the exhaust emission regulations and the battle against an Earth-wide temperature boost. Also is associated with increasing the possibility of the trigger the charge auto-ignition and controlling the HCCI engine combustion phasing problems. However, the point of the present work is to explore the impact of a few potential added substances, such as Hydrogen and the Dimethyl ether (DME), on the ignition behaviors of a Natural Gas HCCI engine. This was done by utilizing hydrogen gas and DME fuel added substances in CNG/HCCI engines to control the start of combustion timing, avoidance of knock, and extension of the working area

the compression ignition principal, as in a diesel engine [5]. In spite of the fact that the scheduling of auto-ignition process is critical to the engine operation; the ignition events is not activated by an external occasion, for example, the beginning of the fuel injection or by the start plug timing. Besides, the rate at which combustion heat release is not influencing by the fuel injection process, similar to the diesel engine, or by fire spread, as with spark ignition engines. However, the partially premixed lean charge compression ignition engine can be used as an intermediate stage between the conventional and HCCI engine in order to reduce the NOx and PM emissions, simultaneously [6]. The essential working rule of HCCI engine at the various working condition, for example, the charge temperature, pressure proportion, and engine speed were assessed [7]. The outcomes demonstrate that the satisfactory operation of the HCCI engine has extremely limited by the lean charge of the air-fuel mixture and the engine operation has kept away from the stoichiometric condition [8]. Moreover, the homogeneity of the freshly charged mixture with the residual combusted gasses inside the engine cylinder has been studying [9]. The inhomogeneities of the charged mixture inside the burning chamber were discovered with the guidance of a stochastic model for the HCCI engine [10]. The model has been accounted with complete chemical oxidation which comprising from 53 chemical species and 590 elementary reactions. These days the looking for the nonpetroleum fuels is the principal concern of the worldwide researcher because of the expanding worries on the lack of alternative fuel supplies and environmental contamination. The alternative fuel, for example, biogas is showing a one of a good kind of the atomic structure. Those natural gas is the best choice for the application of HCCI engine because of it has highest hydrogen ratio so it can produce a lower percentage of CO2 in the exhaust pipe [11,12]. Currently, the suggested innovative technology for the use of CNG in the HCCI engine is directed toward the use of Compressed Natural Gas (CNG)-Hydrogen blends (HCNG) [13–15]. Those, make the reactivity of fuel amid the ignition procedure is yield less middle of the road segments. However, the higher Octane number (ON) of the natural gas fuel prescribes it to use in the HCCI engine burning. In any case, that will guarantee the utilization of the higher compression ratio with 16

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replacing the traditional direct fuel injection framework to a homogenous air/fuel blend inside the engine intake manifold. Notwithstanding, the fuel is supplied inside the manifold to upgrade the blending properties of the fuel with the charged air. The engine and the measuring device have orchestrated as appeared in Fig. 1. The “Kistler” piezo-electric pressure transducer has mounted on the barrelhead, which associated with the engine analyzer gadget through the “Kistler” charge amplifier. Crankshaft angular position (encoder device) has carried out by utilizing an electro-attractive sensor, which mounted on the engine crankshaft with a specific end goal to correspond the incylinder pressure information.

in such engines. In our proposed system, hydrogen will expand the working scope of CNG HCCI engine and diminish the regulated emissions significantly, while DME will assume a noteworthy part in controlling the auto-ignition timing of the HCCI ignition, particularly at low admission air temperature. Finally, the engine operating a range of CNG HCCI engine will be presented as a function of each fuel dose precisely. 2. Experimental study A single cylinder diesel engine has utilized in the present study after

1-

CNG Bottle

2-

Gage Pressure

3-

Liquid DME Pump

4-

Hydrogen Flow Meter

5-

CNG Flow Meter

6-

Air Flow Meter

7-

High Speed Air Blower

8-

Surge Tank

9-

Electric Heater

10-

Temp. Control System

11-

Mixing Chamber

12-

Temp. Sensor

13-

Temp. Sensor

14-

AC Power Supply

15-

Automatic Switch

16-

Hydrogen Bottle

17-

DME Bottle

18-

N2 Bottle

19-

Digital Balance

20-

DME Injector Nozzle

21-

Oil Temp. Sensor

22-

Temp. Reader

23-

Engine Analyzer

24-

Diesel Engine

25-

Dynamo. Controller

26-

Elect-Magnetic Sens.

27-

Eddy Cur. Dynamo.

28-

Co. Water Temp. Sens.

29-

Flue Gases Direction

30-

Exhaust Temp. Sens.

31-

Charge Amplifier

32-

Piezo-Electric Tarns.

33-

Temperature Reader

34-

Exhaust Gas Analyzer

35-

Temperature Reader

36-

Lambda Sensor

Fig. 1. The test devices and the engine experiment arrangement. 17

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fire circumstance, both materials may soften, making the seal fall flat. It has reasoned that metal-to-metal seals utilizing non-ignitable metals would be the best sort of seal.

The intake air, exhaust gas, coolant water, and lubricating oil temperatures have measured amid the engine steady state operation. The admitted air temperature was acclimated to be steady among the exploratory time by utilizing the input control framework, which represented in Fig. 1. The pressure-driven dynamometer has connected with the engine to keep and control its speed at altered load operation. The Compressed Nature Gas (CNG), Dimethyl ether (DME), and Hydrogen fuel system arrangements of the engine have explained in Fig. 1. The Dimethyl ether fuel system have pressurised by the high-pressure Nitrogen bottle, which can prevent the Dimethyl ether vapour blockage in the fuel supply framework. Therefore, as to improve the spray, the injector with Pintle nozzle mounted close to the inlet port of the cylinder head utilising a blending chamber. Before the engine intake manifold, there is a stable surge tank supported with synchronised electric heater operated on a closed lope control framework, as appeared in Fig. 1, is framed to manage the charged air temperature. The blending chamber (Section 11 in Fig. 1) has utilized to premix the charged air, and the fuels blend prior engine intake valves. The blends comprise from Dimethyl ether as a vapor, Compressed Natural Gas, and hydrogen fuel. The utilized vaporous fuels with different portions have supplied from an arrangement of high-pressure cylinders and metered independently using different combinations of pre-calibrated stream meters devices. The barometrical temperature in the engine test lab has typically looked after consistent, around 30 °C. There is an electric admission air heater, which makes the admitted air temperature physically under control. The safety precaution related to the use of alternative gaseous fuels such as Compressed Nature Gas (CNG), Dimethyl ether (DME), and Hydrogen should consider in the engine test conditions. However, the safety precaution totally depends on the chemical and physical properties of the used fuels. Accordingly, some important properties of the utilized gausses fuel have presented in Table 1. Nevertheless, hydrogen gas has classified as a superior auto-ignition temperature when compared with DME and compressed natural gas. In any case, the low ignition energy of the fuel makes it all the more promptly ignitable. The hot air-stream with a temperature of 943 K and 1493 will ignite the hydrogen and methane, respectively. Subsequently, hydrogen can be ignited without much effort off by a stream of hot ignition items transmitted from a neighboring area. The test-rig framework has constructed to limit the Dimethyl ether spillage into the engine chambers, crankcase lubricating oil sump, fuel injection pump, and to limit the likelihood of a fire/blast. DME has known to influence many sorts of plastics and rubbers, except for “Polytetrafluoroethylene” PTFE and butyl-n (Buna-NTM) rubber. In any case, it has discovered that Dimethyl ether additionally creates low temperatures upon vaporization and temperature cycling of PTFE causes embrittlement, which may prompt valve seal breakdown. In a

2.1. Uncertainty analysis An uncertainty issue moreover requests to be located on the records, due to the regular and arbitrary errors exist in the testing activity. Ordinary measures [26] are applied to achieve more than 95% assurance space during the measurements. The determination of the uncertainty for a particular experiment has defined by Eq. (1) as follow:

B 2 δ M = 2 ⎛ ⎞ + (SX )2 ⎝2⎠

(1)

where B is the total regular error in the measurement and SX is the arbitrary error present. The total regular error (B) has calculated by utilizing Eq. (2) as follow: 1/2

K

⎡ ⎤ B = ⎢∑ bi2 ⎥ ⎣ i=1 ⎦

(2)

where bi is each elemental systematic error and K is the total number of regular error sources. However, the arbitrary error knows by applying equation (3):

SX =

1 ⎡ 1 N −1 N⎢ ⎣ P

1/2

Np

∑ (XPk − X¯P )2⎤⎥

(3)

⎦

k=1

where, N is the number of measurements, NP and Xp are the earlier measurement number and measurement value which recorded by the device during the test, and X¯p has set by equation (4):

1 X¯P = NP

Np

∑ XPk

(4)

k=1

The uncertainty of the obtained data (like fuel mass flow rate and the engine torque) is considered from numerous testes data is defined by Eq. (5) as follow:

δR =

(θ1 δ M1)2 + . .. + (θk δ Mk )2

(5)

where δMk is the uncertainty in all obtained data and θk is the sensitivity coefficient of the result to any modification in the obtained tested values. Table 2 records the regular uncertainties for the main apparatus of the engine test facilities. 3. Numerical model A mixture of the compressed natural gas (CNG) and Dimethyl ether

Table 1 Comparison of the Properties of Hydrogen, Methane (represent CNG), and DME at ambient conditions [23–25]. Property

Hydrogen

Methane

DME

Normal state at 289 K and Ambient Pressure Boiling Point at Atmospheric Pressure Liquid Density at Normal Boiling Point (NBP) Vapor Density at NBP Limits of Flammability in Air *Lower Flammability Limit *Upper Flammability Limit Stoichiometric (Volume) Composition in Air Autoignition Temperature Max. Flame Temperature Heat of Combustion Molecular Diffusivity (Gas in Air) Limits of Detonability in Air * Lower Detonability Limit * Upper Detonability Limit Minimum Ignition Energy

Gas 20.3 K 70.8 kg/m3 1.34 kg/m3 Volume Concentra. 4.0% 75.0% 29.53 % 858 K 1800 K 120 MJ/kg 6.1 × 10-5m2/s

Gas 112 K 422.6 kg/m3 1.82 kg/m3 Vol. Concentra. 5.3% 15.0% 9.48 % 813 K 1495 K 50 MJ/kg 1.6 × 10-5m2/s

Gas 248 K 710 kg/m3 1.62 kg/m3 Vol. Concentra. 3.4% 18.6%

18.3% 59.0% 0.02 mJ

6.3% 13.5% 0.29 mJ

5.1% 15.4% 0.22 mJ

18

508 K 27.6 MJ/kg

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Table 2 Measuring instruments and uncertainties. Instrument

Function

Uncertainty

Units

NI data acquisition board Eddy Current Dynamometer Air Flow Meter Fuel Flow Meter

Acquire and log data Measure engine torque

0.00565 0.125

volts Newton

Measure air flow rate Measure fuel consumption Measure exhaust concentration Measure engine temperature

0.5 0.1

m3/hours grams

3.8

% of reading

1.4

Degrees C

Exhaust gas analyzer K-type thermocouple

γ VT ⎡ ⎤ W = ⎢ ⎜⎛C11 − C12 swiral ⎟⎞ ⎥ S¯p + C2 d i (P−Pmotored) ¯p S P i Vi ⎠⎦ ⎣⎝

(10)

dQ i,cond ∂T = - KAi dt ∂Z

(11)

dQBL,conυ = h(Twall − TBL)Awall dt

(12)

dm out,i dQ i,mtran dmin,i Hout Hin − = dt dt dt

(13)

dYk,i ω̇ k,i Mwk = dt ρi

(14)

The champers pressure is predicted by utilizing Eq. (15) at each time step.

(DME) burning and the forming of the exhaust emission have been numerically solved by utilizing CHEMKIN code [27]. The homogeneous gas-phase energy equations with the chemical kinetic were simultaneously simulated unravelled at various HCCI engine geometry and operating conditions [28]. The Woschni heat transfer correlations were executed in our prediction procedure since it has regularly utilized for the HCCI engine reenactment [19,29]. The Woschni correlation and the convection heat transfer rate and coefficient are defined by equation (6) and (7) as follows.

Q̇ wall = h A (T−Twall), h= 129.8 B−0.2P 0.8T−0.55W 0.8

dQ i,cond dQ i,conυ dQ i,mtran dQ i = + + dt dt dt dt

nz

P=

mi Mwi nz V ∑i = 1 Ti i

RU ∑i = 1

(15)

Eqs. (16)–(20) are employed in the in-cylinder gaseous exchange process and are solved altogether. ns

c υm

(6)

dYj dT + m∑ uj + dt dt j= 1

= −P

dYj

(7)

dt

C11 = 2.28, C12 = 0.38, and C2 0.0 for compression =⎧ −3 for combustion and expansion ⎨ 3.34*10 ⎩ The chamber ignition schedule is followed and examined by utilizing the engine heat release sub model. Likewise, the chemical kinetics mechanism of the CNG/DME fuel blend contained 99 species and 477 elementary reactions. The chemical kinetic mechanism is competent to foresee the burning attributes of the fuel blend which containing 10 and 20% of the hydrogen fuel in the entire CNG/DME blends by volume. As the underlying condition for prediction, it was expected that the admission valve closes before TDC with 138 OCA with a barrel pressure of 0.95 bar, which creates the best fuel free pressure profile around the engine Top Dead Center (TDC). Anyway, another engine particular expected in this examination has appeared in Table 3.

=

ρ

(17)

dQconυ = h(Tw − T)Awall dt

(18)

m P= R uT Mw

(19)

⎜

⎟

dWi dV =P i dt dt

ns j= 1

1

dm C A P ⎛ Pd ⎞ γ = D R U 1 dt (RuTu ) 2 ⎝ Pu ⎠ ⎟

2γ ⎡ Pd ⎢1 − ⎛ ⎞ γ − 1⎢ ⎝ Pu ⎠ ⎣ ⎜

⎟

γ

γ−1 γ ⎤

Pd 2 ⎞1−γ ⎟ ⎥ if ⎛ ⎞ > ⎜⎛ ⎥ ⎝ Pu ⎠ ⎝ γ + 1⎠ ⎦ ⎜

⎟

(21) Table 3 Engine specifications.

dmj dt

(19)

The techniques of the charged volume flow rates crossing through the engine valves are predicted based on the explanation presented in Reference [32]. These principles are revealed in Equations (21) and (22). In these equations, all the coefficients and constant are calculated and proposed based on the assumption elucidated in Reference text [33–35].

(7)

∑ ujYj

(16)

1 dV 1 dθ 1 dθ − (Cr 2 − sin2 θ)− 2 (−sin 2θ) ⎞ ⎞ = Vc ⎛ (Rc−1) ⎛sin θ dt 2 dt 2 dt ⎠ ⎠ ⎝ ⎝

A single zone methodology is utilizing to simulate the HCCI engine auto-ignition and combustion process. In-cylinder pressure has suggested to being homogeneous at every calculation instant. Also, the temperature and the in-cylinder gaseous have recommended being identical as well. The first law of thermodynamics equation and the chemical kinetics equations are solving, all together. Equations (7)–(14) are the governed equations. However, the proposed model has specifically elucidated in the available documents in the previous work [30,31].

ns

dt

ω̇ j Mwj

3.1. Basic theories of Single-Zone combustion modeling

dYj dui dT = Ciυ mi i + mi ∑ uj + dt dt dt j= 1

j= 1

dV dmin dm out dQconυ Hin − Hout + + dt dt dt dt

⎜

dUi dWi dQ i =+ dt dt dt

ns

∑ ujYj dm

(8)

No:

Details

Qualifications

1 2 3 4 5 6 7 8 9 10 11 12 13

Number of engine cylinders Engine Rated power Engine displacement volume (cm3) Engine Connecting Rod/Crank Radius Ratio Engine Compression Ratio Cooling type Bore – Stroke (mm) Connecting Rod to Crank Radiuses Bore (cm) Cylinder stroke (cm) Intake valve close ABDC Exhaust valve open BBDC Cylinder wall temperature (K) for wall heat transfer correlation model Engine Speed (RPM)

01 6 kW(8HPat1500RPM) 845 3.75 17.1 Air cooled 87.5 × 110 3.714 9.52 11.45 42° −44° 425

14

(9) 19

1500

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dm C A P 2 ⎞ γ + 1 ⎛ Pd ⎞ ⎛ 2 ⎞ γ if ⩽⎜ = D R U1 ⎛⎜ ⎟ ⎟ dt (RuTU ) 2 ⎝ γ + 1 ⎠ 2(γ − 1) ⎝ Pu ⎠ ⎝ γ + 1 ⎠ 1 − γ ⎜

ϕ=

⎟

(22)

(F / A) Actual (F / A) stoich

(23)

The inverse of (Φ) is defined as (λ), which is known by the relative air/fuel ratio and can be expressed as in equation (24); 4. Results and discussion

λ=

The examination of the HCCI engine elucidates that the in-cylinder pressure data can be used to predict the efficient operation in the case of normal and abnormal engine combustion. However, the engine chamber pressure during knocking combustion is showing a sharp rise and a strapping variation. The rate of the pressure rise and pressure rise acceleration oscillates more aggressively, and their peak enlarged extremely and moved forward a bit. Fig. 2 shows the in-cylinder pressures at different engine load and condition of serious, small, and no-knocking combustion at a constant engine speed of 1200 RPM. The HCCI engine is fueled with pure Dimethyl ether and run at different engine load until the engine knocking is reached. As can be seen from Fig. 2, at the conditions of the serious knocking combustion, the combustion process is progressed on significantly. In small knocking and no engine, knocking the in-cylinder pressure fluctuation is lower. Consequently, it is clear from the obtained results that, if the maximum values of the in-cylinder pressure occur before the engine top dead centre (TDC) that will lead to the rapid increase of the in-cylinder pressure oscillations. The obtained results elucidated that the strength of the engine knocking will increases if the in-cylinder peak pressure takes place during the compression stroke. However, during the high load operation, the maximum pressure inside the engine cylinder should be delayed to occur after the TDC with 5 crank angle degrees to avoid the engine knocking. However, the use of the EGR and different fuel type commixture will reduce the in-cylinder charge reactivity and can delay the combustion phasing, which will decrease the possibility of engine knocking. That finding will be helpful during the present simulation analysis which used to determine the conditions of the engine knocking and misfire conditions.

(A/F ) Actual (A/F ) Stoich

(24)

To predict the HCCI engine operation numerically or experimentally the several measures of the mixed fuels must be resolved. The measure of every fuel provided into the engine as far as the separate fuel stream rate is characterized as the relative air/fuel ratio (λ ), which computed by equation (25–27). o o λCNG = mAir /(mCNG ∗ (A/F ) CNGstoich)

λDME =

o o mAir /(mDME

∗ (A/F ) DME Stoich)

o λH 2 = mAir /(mHo 2 ∗ (A/ F ) H 2Stoich)

(25) (26) (27)

And the total relative air/fuel ratio is defined by equation (28): o o λTotal = mAir /(mTotal Fuel ∗ (A / F ) Total fuel Stoich ) o o o o mDME , mHo 2 , and mTotal where mAir is the air flow ratemCNG Fuel are the flow rates of natural gas, DME, hydrogen, and the total fuel mixture, (A/ F ) T respectively.(A/ F ) CNG Stoich (A/F ) DME Stoich , and otal fuelStoich are the stoichiometric air-fuel ratio of natural gas, hydrogen, DME, and the total fuel mixture, respectively. As can be seen from Fig. 3 the admission of the various measure of the CNG fuel into the intake port of HCCI engine fluctuated with the various measure of Dimethyl ether (DME) added by volume in the case of different engine blends equivalence ratio. The results of the engine simulation demonstrate that at high engine load operation, the knock like the ignition is affirmed in which the total fuel (CNG + DME) equivalence ratio is 0.5. Also, the low load operation is limited by the misfire condition which combined with the smallest amount of equivalence ratio of 0.15. Anyway, the HCCI engine fueled with CNG has experienced misfire operation if the charge temperature is changed to be 25 °C. To defeat that issue, the several measures of DME fuel have been added to upgrade the charged fuel/air-reactivity. By a stage increment of the volume division of DME fuel in the blend of

4.1. Determination of the HCCI engine working region The operating region of the HCCI engine under specific working conditions is numerically determined. This region is confined by the two boundary limits. The knock like burning is the first boundary in which the blends of the fuels are getting to be rich. The failure (misfire) operation is the second one where the charge blends step forward toward the lean fuel concentration. Thus, the engine working area can be characterized by the rate of the fuel in the charged air/fuel blends which make the auto-ignition procedure is possible. This can be measured by knowing the aggregate consumption of the utilized mixed fuel supplied to the engine. However, the point of the present examination is to contemplate the likelihood of utilizing the option of non-petroleum based fuels as added substances to the natural gas HCCI engine. Anyway, if any fuels, for example, hydrogen or DME is introduced as added substances that would require an alteration in the first measure of the natural gas supplied to the engine to keep the engine speed and load consistent over once more. Above and over, the present research movement is concentrating on the exact assurance strategy for the distinctive fuel mass flow rate o (mFuel ) which keep up the engine speed and load consistently while including the diverse measure of the fuels as added substances to the fundamental CNG fuel. However, to make out the engine working conditions region the aggregate sum of the mixed fuels per the measure of wind stream provided to the engine must be resolved. That amount is regularly used to show if the fuel/air is rich, lean, or stoichiometric and known as the fuel-air equivalence ratio (ф) and can be gotten by Eq. (23)

Fig. 2. Experimental finding for the In-cylinder pressures data at different types of knocking combustion [Engine speed 1200 RPM Fore DME HCCI Fuel supply]. 20

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Fig. 5. Engine operating region as a function of CNG fuel supply and the total blends of CNG/DME at different hydrogen addition. Fig. 3. HCCI engine working region at the different total fuels mixture equivalence ratio with varying the amount of CNG fuel and different amount of Dimethyl ether (DME) fuel blends.

The impact of hydrogen in the blend of natural gas/DME fuel mixes has predicted. However, the Eqs. (3–6) have connected to ascertain the adjustment in the estimation of the DME, hydrogen, and CNG fuel relative air/fuel ratio at a various engine total equivalence ratios. Anyway, the impact of 10 and 20 % of the hydrogen mole fraction in the entire fuel blend at different engine total blend equivalence ratios has studied. The acquired results of the impact of hydrogen dose on the adjustment in the extent of DME and CNG in the total fuel blend and its effects on augmenting the engine-working region have illustrated in Figs. 4 and 5. Where the information of Fig. 4 explained that by including 10% of hydrogen volume part into the blend of CNG/DME fuel the engine working area is stretched from both the knocking and misfire limit sides when distinguished with 20% of hydrogen in the blend. This is because of the impact of hydrogen fuel for smothering the low-temperature reaction. This impact is more declared if the hydrogen mole portion in the blend expanded to 20 % by volume. Likewise, the consequences of Fig. 5 demonstrate that expanding the hydrogen mole portion will reduce the classical burning district and the capacity of expanding the scope of CNG fuel extent in the blend is decreased. Expanding the CNG stream rate will require more stream rate of DME fuel. Finally, to cover the relationship between the working regions of the HCCI engine at various alternative fuel dosages the information of Fig. 6 must be utilized. However, the ordinary working conditions of the engine appeared in Fig. 6, which demonstrates the impact of 20% of the hydrogen mole division and the variety in the amount of both CNG and DME fuel on the effective engine-operating region.

Fig. 4. Engine working region as a function of DME fuel supply and the total blends of CNG/DME at different hydrogen additives.

CNG + DME, the engine will ready to run easily. Nevertheless, if the DME rate expanded suddenly at a settled measure of CNG fuel the engine knock will be observed. The acquired results demonstrate that the typical burning extent (as appeared in Fig. 3) of the engine gets to be smaller with the increase of engine load. Additionally, it was demonstrated that the conceivable working range is genuinely wide from λtotal equal 2 until 6.66 which equivalent to the total equivalence ratio of 0.5–0.15. The acquired results recognize the engine ignition and knocking limits with various DME and natural gas relative air/fuel proportion at different engine working scales for the total blend equivalence ratio. In which, the engine misfire limit generally stays unaltered at different estimations of DME relative air/fuel proportion (λDME ) when the estimate of CNG relative air/fuel ratio (λNG ) is changed.

4.2. Engine performance characteristics study The impact of DME and hydrogen fuel added substances into CNG fuel in HCCI engines have researched numerically and experimentally at normal combustion regions, which were characterized beforehand. Amid our study, we utilize a settled measure of DME at two load conditions and two unique instances of hydrogen fuel added substances. The measured dosage of CNG and H2 have appeared on the Table 4 where the measure of compressed natural gas diminished with the increase of hydrogen mole portion in both of our load conditions. Figs. 7–10 demonstrate the subsequent variety of the in-barrel pressure, typical temperature, the rate of heat release, and gathered heat release with various percentages of hydrogen and CNG in the fuel blend under 21

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Fig. 6. Final engine working region at different fuel portion and the entire fuel mixture relative air/fuel ratio in the case of using 20 % of hydrogen blend. Table 4 Different fuel portion in the cases of successful engine combustion at two load conditions. Test load condition

Low load condition

Total or (Total Equivalence ratio) The case of CNG/DME mixture without hydrogen addition

0.25

0.45

λ

12

The case of CNG/DME mixture with 10 % hydrogen mole fraction addition

λ λ λ λ

The case of CNG/DME mixture with 20 % hydrogen mole fraction addition

λ λ λ

1/λ

CNG

DME CNG DME H2 CNG DME H2

Case 1

High load condition 3.5

Case 4

6

6 12.62 6 199

Case 2

13.5 6 91

Case 3

3.6

Case 5

6 101 3.8 6 46.6

Case 6

two ostensible engine loads. In these Figures, DME portions were constant at certain esteem, which makes the distinctive instances of inspected blend ignited. It can be watched that by expanding the engine load the chamber top pressure, the pinnacle of heat release rate, and the in-barrel extreme temperature are expanded essentially. These are seen with and without

Fig. 7. In-cylinder predicted pressure profile via the engine crank angle at low and high loads with two percentages of hydrogen mole fractions. 22

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Fig. 10. In-cylinder accumulated heat release profile via the engine crank angle at low and high load with two percentages of hydrogen mole fractions.

Fig. 8. In-cylinder temperature profile via the engine crank angle at low and high loads and two percentages of hydrogen mole fractions.

Fig. 9. In-cylinder rate of heat release profile as a function of crank angle at low and high load with two percentages of hydrogen mole fractions.

Fig. 11. Prediction and experimental data of pressure tracing of CNG/DME fuel blends without hydrogen additives at the low and high load condition.

hydrogen increase into the fuel blend. Likewise, the auto-ignition timing is retarded with the rise in the engine load, and the hydrogen mole part has appeared in Figs. 7 and 8. These results support our allegation that the hydrogen fuel as an alternative fuel additive will work to expand the operating area for the HCCI engine. To examine the approval of our prediction results with the engine experiment, we select situation one and 4 in the Table 4 above. Those to consider both the low and high load condition in the stat of CNG/DME fuel blend without hydrogen increase and select stats 3 and 6 to regard the blend of 20 % of hydrogen mole portion. The outcomes have appeared in Figs. 11 and 12. These Figures demonstrate a sensible harmony between both prediction and engine-exploratory results at two inspected loads and two rates of hydrogen increase.

5. Conclusion By mixing Dimethyl ether (DME) and hydrogen (H2) fuels with Compressed Natural Gas (CNG) it was probably to attain a stable operation of the HCCI engine at different load condition. By applying a different amount of the Dimethyl ether and hydrogen fuels into the inlet air, it was possible to adjust the engine combustion phasing to avoid the knock-like combustion phenomenon. By this method, it was achievable to study the connection between the Dimethyl ether and hydrogen fuel additive percentage, the inlet air/fuel quantity and the CNG needed to get auto-ignition close to Top Dead Center (TDC). Different fuel mixture ratios of CNG, Dimethyl ether and hydrogen fuel have also tested in the same manner. All examinations were approved at different air/fuel equivalence ratio from 0.15 to 0.50. The impact of DME and hydrogen fuel added substances into CNG 23

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[6]

[7] [8]

[9]

[10]

[11] [12] [13]

[14]

[15]

Fig. 12. Prediction and experimental data of pressure tracing of CNG/DME fuel blends with 20 % of hydrogen mole fraction at the low and high load condition.

[16] [17]

fuel in HCCI engines have predicted numerically and experimentally. A chemical kinetic mechanism merged with a Zero-Dimensional model have been utilized to calculate the auto-ignition and combustion of CNG/DME fuel blends with the impact of 10 and 20 % of hydrogen mole portion. The obtained results elucidated that by adding hydrogen into the blends of CNG/DME fuel the engine operation region will be expanding from the knock limit side. However, if the mixture of CNG/ DME fuel containing a small amount of hydrogen the ignition will be retarding rather than that without hydrogen. As engine load increases, the required CNG amount in the mixture blends to meet the necessity of knocking and misfire restrictions will be expanded. Besides, any increments of CNG stream rate requests more stream rate of DME fuel and this amount will be fundamentally varying the amount of hydrogen dose in the whole fuel blends. However, the predicted results support our planned method to develop the working engine region, particularly at high load conditions. Furthermore, the DME fuel is capable of igniting the charged blends whether H2 additives substances has employed to smooth the blend reactivity and retarding the ignition to happen after the cylinder TDC. Moreover, there is a reasonable agreement between both of the engine experimental results and engine test prediction of the in-chamber pressure illustration data.

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