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Article

Inner Selective Non-Catalytic Reduction Strategy for Nitrogen Oxides Abatement: Investigation of Ammonia Aqueous Solution Direct Injection with an SI Engine Model

by
Fengshuo He
1,2,
Xiumin Yu
1,2,*,
Yaodong Du
1,2,
Zhen Shang
1,2,
Zezhou Guo
1,2,
Guanting Li
1,2 and
Decheng Li
1,2
1
State Key Laboratory of Automotive Simulation and Control, Jilin University, Changchun 130022, China
2
College of Automotive Engineering, Jilin University, Changchun 130022, China
*
Author to whom correspondence should be addressed.
Energies 2019, 12(14), 2742; https://doi.org/10.3390/en12142742
Submission received: 17 June 2019 / Revised: 6 July 2019 / Accepted: 15 July 2019 / Published: 17 July 2019
(This article belongs to the Section B: Energy and Environment)
Browse Figures
Versions Notes

Abstract

:
This study contributes to a method based on an aqueous solution of ammonia direct injection for NOx emissions control from internal combustion engines. Many previously published studies about deNOx technology are based on selective catalytic reduction (SCR), but only few deal with inner selective non-catalytic reduction (inner SNCR) technology, which is an intensive improvement of selective non-catalytic reduction (SNCR) applied in the in-cylinder purification procedure. Before numerical calculations were carried out, the computational fluid dynamic (CFD) simulation model was validated with steady-state experimental results. The main results revealed that with the increasing concentration of aqueous solution of ammonia, nitrogen oxides gradually decrease, and the largest decline of NOx is 65.1% with little loss of cylinder peak pressure. Unburned hydrocarbon (UHC) and carbon monoxide (CO) may increase using inner SNCR, and soot emissions show a decreased tendency. However, there is little change when ammonia content varies. Ulteriorly, refining the direct injection phase is of great help to inner SNCR technology to enhance the reduction of NOx and reduce NH3 oxidation and NH3 slipping.

1. Introduction

The Volkswagen emissions scandal once again attracts people’s attention to automobile exhaust emissions, especially NOx emissions. With the emission regulations becoming more and more stringent, exhaust treatment technologies for engines need to be upgraded and adjusted. As common technical routes to reduce NOx emissions, two schemes are often mentioned: water injection or water fuel emulsion and selective catalytic reduction (SCR) [1,2,3,4,5]. In this section, these two schemes are briefly reviewed and an innovation scheme is put forward.
Much of the literature shows that both water injection and water emulsion will enhance fuel conversion efficiency and promote NOx emission reduction [6,7]. Parlak et al. [8] developed an electronic controlled steam injection system in the intake manifold for an spark ignition (SI) engine. In the experimental results, it is seen that the engine torque and the effective power increase up to 4.65% at 3200 rpm, specific fuel consumption reduces up to 6.44% at 2000 rpm, and NO emissions reduces 40% on average at 2800 rpm. Yang et al. [9] conducted a detailed experimental study to evaluate the effect of 10% water emulsion diesel on engine performance and emissions. The result shows that lower exhaust gas temperature and lower NO emissions are achieved at all load and engine speed condition for 10% water emulsion diesel as compared with diesel fuel. Adnan et al. [10] conducted an experimental investigation on the optimum water injection timing for power augmentation and emission control of a hydrogen fueled compression ignition (HFCI) engine. The results show that a longer injection duration introduces more water droplets into the cylinder, reducing the in-cylinder charge temperature, which leads to NOx reduction. Although, the amount of water by injecting or emulsifying requires special attention. Excessive water injection may lead to decreased power performance and increased incomplete combustion [11]. Thus, the NOx emissions are limited by increasing the amount of the injected water.
SCR has been widely applied in the exhaust after-treatment device of internal combustion engines (ICE). Compared with the three-way catalytic converter (TWC), SCR is not strictly restricted by the equivalence ratio [12]. Thus, the application of SCR has more rationality and scientificity in lean burn gasoline engines and diesel engines. However, the traditional SCR technology has some blemishes, such as poor durability of SCR catalyst [13], narrow temperature window for active deNOx [14], catalyst deactivation due to particulates accumulation [15], catalyst poisoning effect caused by heavy metals (Pb, Zn, and so on, and their oxides) [16], high cost, and difficult recovery by using the noble metal catalysts. The miniaturization and compactification of SCR equipment are also very important factors, which influence the automobile lightweight, especially the passenger car [17]. These limitations led researchers to begin to focus on selective non-catalytic reduction (SNCR), which is another technical route to reduce NOx emissions. As a result of getting rid of the reliance on catalysts, engines with SNCR technology are less fussy about working conditions and fuel quality. Nevertheless, studies have shown that the efficient implementation of SNCR has strict requirements for the deNOx temperature window. Nowadays, SNCR is widely applied in emissions after-treatment equipment of thermal power plants [18], but reports about SNCR applied in ICE are relatively rare [19].
Ammonia can be used as fuel surrogate for ICE or used as a reducing agent in after-treatment units for the SCR or SNCR process [20,21,22,23]. Ammonia can be easily liquefied for storage at a relatively low pressure (1.034 MPa) and ambient temperature or cooled to 240 K for storage at ambient pressure. Ryu et al. [24] performed a series experiments separately on a spark-ignition engine with ammonia blended hydrocarbon fuel and expressed their idea that a high injection pressure can increase the flow rate of the anhydrous ammonia; however, if the injection pressure is too high, ammonia will be liquefied, which has an impact on quantitative research. Meanwhile, ammonia is a double-edged sword. On one hand, as a carbon free energy storage medium, it does not produce CO2, CO, and unburned hydrocarbon (UHC) emissions after burning [25]. On the other hand, an unreasonable supplying strategy can lead to NOx emissions deterioration and ammonia slip [26]. Therefore, how to utilize ammonia in ICE for NOx reduction could be an interesting issue.
It is an ideal method to add ammonia into ICE in the form of aqueous solution compared with anhydrous ammonia. NH3·H2O, the principal component of aqueous solution of ammonia, is easily decomposed to produce ammonia and water by heating. Thus, considering the coupled effect of ammonia and water for NOx reduction may be of great significance to deNOx. An improved NH3·H2O-SNCR process based on direct injection of aqueous solution of ammonia, namely inner selective non-catalytic reduction (inner SNCR), is proposed in this work. Comparing the inhibitory effect of pure water injection on NOx emissions, the formation of NOx is further inhibited by NH3·H2O-SNCR. This proposal is based on gasoline port injection (GPI) and aqueous solution of ammonia direct injection, which will contribute to mitigating NOx emissions, as well as simplifying the layout of the after-treatment system, innovatively. The investigation on inner SNCR coupled with the numerical computational fluid dynamic (CFD) method is reinforced in this work. Previous studies of our research group [27,28] focus on combined injection technology with a dual fuel spark ignition (SI) engine, which is expediently modified for aqueous solution of ammonia direct injection when calibrating. On the basis of the goal of removing NOx without causing other negative effects, this work will enhance understanding of the coupled effect of water and ammonia in refined CFD perspectives for reducing NOx under the stoichiometric condition.

2. Modeling Methodology

2.1. Geometric Model and Boundary Conditions

In this work, CONVERGE software [29] with kinds of sub-models was utilized to build and calibrate the engine research model. The virtual engine was modified from a four-cylinder SI engine and the main technical parameters are shown in Table 1.
On the basis of reverse engineering, a stereolithography (STL) file for a single cylinder of the commercial engine and its attachment (manifolds and valves) was obtained from 3D point clouds. Figure 1 shows the structure body (A), the surface mesh (B), and the two-dimensional section (C and D) of the structure mesh at 23 °CA after top dead centre (TDC).
SAGE, a detailed transient chemistry solver developed by Senecal et al. [30], was chosen as the combustion model for various reaction processes. This model calculated the chemical reaction rate of each step. The more detailed the chemical reaction mechanism used in the combustion model, the closer to the actual combustion is the simulation process in the cylinder. However, in fact, the calculating speed will slow down using the detailed mechanism. Taking account of saving computational time, it is necessary to simplify the reaction mechanism according to the recorded experiment results in the previous literature.
The mechanism used in this work is composed of three parts, involving gasoline surrogate mechanism, NOx generation mechanism, and ammonia deNOx mechanism. The primary reference fuel (PRF) mechanism [31] including 41 species and 124 reactions is appropriate for gasoline surrogate. This PRF mechanism has been validated in a series of experiments, such as shock tube, jet stirred reactor, flow reactor, and homogeneous charge compression ignition (HCCI) engine, and it has also been widely applied or verified in other studies [32,33,34]. The NOx mechanism, a so-called extended Zeldovich mechanism, comes from Tao’s work [35], which is widely referenced in published articles [36,37,38]. The ammonia deNOx mechanism is collated and verified by Golovitchev [39] and it has been tested and verified as well [40,41]. This work combines these three sub-mechanisms to simulate the coupled effect of water and ammonia for the engine deNOx process with inner SNCR strategy.
As a widely used empirical model, the Hiroyasu model was employed in the present soot prediction, which could make an all-round evaluation on the comprehensive applicability of the inner SNCR method [42]. Re-normalization group (RNG) k-ε model [43] is used for turbulence simulation. The wall heat transfer model, developed by Han and Reitz [44], is used for the wall heat loss. The Kelvin–Helmholtz and Rayleigh–Taylor (KH-RT) hybrid model [45] is used for fuel injection and spray breakup. In detail, the primary breakup is controlled by the KH model and the sub-droplets are produced in this process. The subsequent breakup is determined by the competition mechanism between KH model and RT model. It is necessary to consider turbulence in the continuous phase with the motion of oil droplets, so the O’Rourke model [46] is chosen for turbulence in this work. A spherical module with energy of 40 mJ simulates ignition by the spark plug at the side of the exhaust manifold. Figure 2 shows the relative locations of the port fuel injector, the direct injector, and the spark plug in the CFD model.

2.2. Initial Parameters and Boundary Conditions

Initial parameters and boundary conditions of the engine model were mainly based on experimental measurement as well as calculation values from GT-SUITE code. For four-stroke engines, it is necessary to make it clear that 0 °CA represents the top dead centre (TDC) for firing in this investigation. Thus, the negative values mean the event happening before TDC and positive values mean the event happening after TDC. Table 2 shows the initial parameters and boundary conditions. The test fuel, gasoline with research octane number (RON) 90, was applied in the calibration based on combustion and emissions. The injected aqueous solution of ammonia was preconfigured with ammonia mass fraction (AMF) of 0%, 10%, and 20%, respectively. The direct injection (DI) timing of the aqueous solution of ammonia was set to −105 °CA, 0 °CA, and 60 °CA, respectively. All of the simulations began at −383 °CA and ended at 120 °CA. In order to facilitate and understand the comparison of the results in Section 3, the cases and the legend nomenclature are shown in Table 3.

2.3. Model Validation

The test experiment system for calibration is illustrated in Figure 3. Detailed information of the test equipment and its accuracy were presented in the work of [27]. In order to ensure the accuracy of the verification, the experiment and simulation were under the same working conditions, namely at the speed of 1500 r/min and at the torque of 40 N·m. Meanwhile, the overall equivalence ratio of 1 was used for the stoichiometric condition. PRF 90 (isooctane: 90% vol. and n-heptane: 10% vol.) was used to match the experimental gasoline with RON 90. Cylinder pressure, heat release rate (HRR), and global NOx emissions were used for calibration, as shown in Figure 4.
In Figure 4, the simulation results coincided with the experimental results at most coordinates. The simulation error was mainly the result of the accuracy error of heat transfer loss and the reduced PRF mechanism. Because the average error was less than 5%, the subsequent results and analysis got sufficient reliable assurance.

3. Results and Discussion

3.1. Cylinder Pressure

In Figure 5a, the DI event occurs before combustion (DI timing = −105 °CA). With AMF increasing, the peak pressure decreases first and then increases when AMF = 20%. The peak pressure change rate is −0.22%–0.37%. This is because that part of NH3 is oxidized, compensating for the pressure drop caused by water. In Figure 5b, the DI event occurs during combustion (DI timing = 0 °CA). A significant delay (0.9 °CA) is observed. However, the pressure is without noticeable changes with the variation of AMF, which indicates no compensation for pressure by NH3 addition. These two cases, DI timing = −105 °CA or 0 °CA, will cause lag of the phase angle corresponding to the peak pressure. Most of the components in the aqueous solution of ammonia are water, the local adiabatic flame temperature decreases in the cylinder due to the phase change of water, which is an endothermic process. Further, the temperature dropping further affects the chemical reaction rate. This is why the crank angle phase is delayed. Water direct injection could promote the formation of a highly humid air/fuel mixture, which inhibits the advance and spread of the flame front. Especially when the injection timing is near the combustion phase (DI timing = 0 °CA), it is likely to cause peak pressure decrease, peak phase angle delay, incomplete combustion, and power decrease as a result of more interference. In Figure 5c, because the direct injection happens after the combustion phase (DI timing = 40 °CA), there is no change in peak pressure and a slight fluctuation (±1.69%) occurs in cylinder pressure after 40 °CA with the variation of AMF.

3.2. Major Intermediates Combustion Species

Variations in highly active radicals such as OH, H2O2, and HO2 can be captured as a crucial indicator to reflect combustion rate and intensity [47]. Figure 6, Figure 7 and Figure 8 show the effect of AMF on OH, H2O2, and HO2 at different DI timings. When DI timing = −105 °CA, there is enough time to form a high humidity mixture before burning. This injection strategy is the same as the inlet port injection or fumigation situation. Water evaporates and absorbs heat, causing the cylinder temperature decrease. Meanwhile, there is a lag in the peak concentration of all species. The hysteresis effect of combustion is inhibited with the increase of ammonia concentration. When DI timing = 0 °CA, the hysteresis is reduced and combustion phase does not change further with variation of AMF. When DI timing = 40 °CA, water (AMF = 0) or aqueous solution of ammonia (AMF = 10% and 20%) injection occurs after combustion phase and most of the curves overlap in different AMF in Figure 6c, Figure 7c and Figure 8c, which indicates very little effect in combustion using inner SNCR. OH has been identified as a marker of combustion occurrence in many literature studies [48,49,50,51]. H2O2 and HO2 also play an important role in high temperature reaction process through #1~#6, which are highly susceptible to water addition, especially causing temperature drop and reaction delay.
#1: C7H16 + O2 = C7H15 + HO2
#2: C8H18 + O2 = C8H17 + HO2
#3: C7H16 + HO2 = C7H15 + H2O2
#4: C8H18 + HO2 = C8H17 + H2O2
#5: HO2 + HO2 = H2O2 + O2
#6: H2O2 (+M) = OH + OH (+M)

3.3. Major NOx Emissions

Most NOx emissions exist in the form of NO in engine cylinders [52,53]. Thus, this fundamental research takes NO as the representative of NOx to evaluate the proposed inner SNCR method. Figure 9, Figure 10 and Figure 11 exhibit the mole fraction evolution of NO emissions in the transverse section of the combustion room under stoichiometric condition at three DI timings.
In order to fully compare the evolution of NO emissions with different DI timings, the image post-processing of the calculated results starts from 50 °CA and ends at 110 °CA. Again, the original baseline represents the NO emissions of the prototype engine without inner SNCR and the AMF value represents the different ammonia concentration in the aqueous solution of ammonia. When AMF = 0, namely pure water injection, the NO emissions show a clear decreasing trend compared with the original baseline in Figure 9, Figure 10 and Figure 11. This can be easily explained that the water injection reduces the in-cylinder temperature and the lower flame temperature inhibits the formation of NOx. On the basis of the theory from Zeldovich [54], thermal NOx production doubles for every 90 K temperature increase when the flame temperature is above 2000 K. Therefore, it can be seen that these results conform to Zeldovich mechanism with different DI timings using water injection method, and similar conclusions appear in the literature [55,56,57]. With the increase of ammonia concentration, the regional concentration of NO obviously shrinks in these three figures, which is because high concentration aqueous solution of ammonia contributes to perfect NO reduction. For DI timing, the retention time of aqueous solution of ammonia in the combustion chamber is longer when DI timing is earlier, so NO emissions performance of DI timing = −105 °CA is better than that of DI timing = 40 °CA. Additionally, when DI timing = 40 °CA, poor diffusion of ammonia slows down NO reduction, so the final NO concentration is still at a high level. Particularly, DI timing = 0 °CA achieved better NO emissions effect than DI timing = −105 °CA and DI timing = 40 °CA. This is mainly because the DI timing (0 °CA) is close to the ignition timing (−13 °CA), which causes greater disturbance and temperature drop at the front of the flame. The consequence is that the peak cylinder pressure and active ingredients are sacrificed, as shown in Figure 5b and Figure 6b. In order to demonstrate the effect of deNOx with the inner SNCR method, compared with the original baseline, Table 4 is calculated and recorded based on the data at the end of the simulation (120 °CA).

3.4. Other Emissions

Figure 12, Figure 13 and Figure 14 show the recorded data at the end of the CFD simulation (120 °CA). As shown in Figure 12, compared with the original values, SNCR technology tends to increase UHC, and the maximum increment is 27.6%; whereas with the increase of ammonia concentration, slightly UHC is suppressed. For most ICE, the wall quenching and the slit effect may deteriorate UHC emissions. In this work, however, the result above is mainly because the mass of the aqueous solution injected in the combustion room is constant. Therefore, the increase of ammonia will inevitably lead to the decrease of water, which is the main deteriorator of UHC. When DI timing = 0 °CA, severe flame interference and heat transfer barriers promote larger generation of UHC than that when DI timing = −105 °CA and 40 °CA. As an additional confirmation for the effect of aqueous solution, Lanzanova pointed that increased air dilution reduces the combustion temperature and lowers post-flame UHC oxidation [58].
In Figure 13, the change of CO concentration is similar to UHC with the variation of DI timing, although their formation mechanism is essentially different. The biggest change took place in DI = 0 and AMF = 20%, with a maximum increase of 15.3%. For incomplete combustion products, inert substances direct injection hinders flame development. On the one hand, the reaction formula, CO + OH = CO2 + H, is the key reaction pathway for CO oxidation to CO2 [59]. On the basis of Figure 6b, an obvious OH decline occurred as aqueous solution was injected, and this inhibits the above-mentioned positive reaction process. On the other hand, a part of ammonia may react with oxygen to produce NOx under high temperature, resulting in local oxygen deficiency, which increases incomplete oxidation of the hydrocarbon fuel. Generally, increase in ammonia concentration leads to a slight increase in CO in these three DI timings.
In Figure 14, there is no obvious soot fluctuation compared with the original baseline (calibrated value), which means that the inner SNCR method maintained good soot tolerance for the addition of ammonia aqueous solution at different DI strategies. When DI timing = −105 °CA and 0 °CA. The earlier DI timing inhibits the formation of soot, mainly as a result of the inhibition mechanism of aqueous solution on high temperature. The maximum reduction is 16.9%. When DI timing = 40 °CA, the DI method of aqueous solution of ammonia plays little effect on soot formation or consumption.

3.5. Contribution of Ammonia

In this work, ammonia was introduced to promote the reduction of NOx on the basis of in-cylinder water direct injection. By counting the types of ammonia reactions in each cell, contribution of NH3 were obtained. In Figure 15, two concentrations (AMF = 10% and 20%) and three DI timings (DI timing = −105 °CA, 0 °CA, and 40 °CA) are analyzed. Additionally, the contribution of ammonia is divided into three parts, for reduction (NH3 + NO → N2 + H2O), oxidation (NH3 + O2 → NO + H2O), and slipping (not involved in any reactions). It is beneficial to analyze the proportion of different effects to promote the positive effects of ammonia and to inhibit the negative effects of ammonia. The contribution sequence for reduction effect is case 1 > case 2 > case 3. The contribution sequence for oxidation is case 2 > case 1 > case 3. The contribution sequence for slipping is case 3 > case 2 > case 1. The above results can be analyzed as follows: contribution for reduction and slipping are mainly related to the retention time of NH3 in the combustion chamber and an early DI timing results in longer retention time and further increases the contribution of NH3 for reduction and decreases the contribution of NH3 for slipping. However, an early DI timing means that more NH3 may be oxidized to NO under high cylinder temperature, which weakens the selectivity for deNOx. Additionally, the increase of ammonia composition is favorable to the enhancement of the deNOx effect, but the contribution of NH3 for reduction is decreased. Thus, ammonia concentration is not likely to increase limitlessly, and DI timing matching the appropriate ignition phase is the best choice to play the maximum positive role of ammonia for inner SNCR.

4. Conclusions

Combining the respective characteristics of water DI technology and SNCR technology, this paper contributed to an innovation method, inner SNCR, which was verified based on CFD scheme in an SI engine model with port fuel injection and ammonia aqueous solution direct injection. A series of results with three AMF values and three DI timings were fully presented under stoichiometric condition. Some main conclusions are summarized as follows:
  • Inner SNCR, an innovate method put forward for ICE, can effectively inhibit NOx emissions with less negative effects. More NO reduction can be achieved by NH3 addition rather than by increasing water injection. With the increase of ammonia composition, the largest decline of NOx is 65.1%, when DI timing = 0° CA for stoichiometric condition.
  • By using ammonia aqueous solution direct injection, the in-cylinder pressure will decrease slightly, and the corresponding phase of peak pressure will lag behind. However, owing to the small amount of injected aqueous solution (about 20% water fuel ratio), the impact on dynamic performance is very small.
  • As a relatively inert component, aqueous solution of ammonia inhibits the rapid accumulation of active radicals in the combustion chamber, which directly leads to retard of combustion reaction rate and delay of peak pressure.
  • Improper ammonia solution injection phase may cause incomplete combustion and an increase in UHC and CO emissions. The maximum increase of UHC is 27.6% and the maximum increase of CO is 15.3%. However, for soot, there is a decline when DI timing = −105 °CA and 0 °CA, and the maximum reduction is 16.9%.
  • The contribution of the ammonia addition is divided into three parts: reduction, oxidation, and slipping. The reduction effect and slipping effect are mainly related to the retention time, so an earlier DI timing helps to strengthen reduction of NO by NH3 and reduce NH3 slipping. Nevertheless, an early DI timing means that more NH3 may be oxidized to NO under high cylinder temperature simultaneously.

Author Contributions

Conceptualization, F.H.; methodology, Z.S., Z.G., G.L., and D.L.; software, F.H.; validation, F.H. and Y.D.; formal analysis, F.H.; investigation, F.H.; resources, X.Y.; data curation, F.H.; writing—original draft preparation, F.H.; writing—review and editing, F.H.; visualization, F.H.; supervision, X.Y.; project administration, X.Y.; funding acquisition, X.Y.

Funding

This research was funded by the National Natural Science Foundation of China, grant number 51276079.

Acknowledgments

The authors appreciate the insightful comments and suggestions from the reviewers and the editor.

Conflicts of Interest

The authors declare no conflict of interest.

Nomenclature

NOxnitrogen oxides
deNOxdenoxtronic
SCRselective catalytic reduction
SNCRselective non-catalytic reduction
CFDcomputational fluid dynamic
CO2carbon dioxide
COcarbon monoxide
UHCunburned hydrocarbon
ICEinternal combustion engine
HFCIhydrogen fueled compression ignition
TWCthree way catalytic converter
Pbplumbum
Znzinc
RONresearch octane number
AMFammonia mass fraction
DIdirect injection
HCCIhomogeneous charge compression ignition
NH3ammonia
H2Owater
NH3·H2Oammonia monohydrate
SIspark ignition
HRRheat release rate
STLstereolithography
TDCtop dead centre
PRFprimary reference fuel
PFIport fuel injection
GPIgasoline port injection
RNGre-normalization group
KH-RTKelvin-Helmholtz and Rayleigh-Taylor
CAcrank angle
NOnitric oxide
N2nitrogen
Hhydrogen atom
O2oxygen
C7H16n-heptane
C7H15n-heptane alkyl
C8H18isooctane
C8H17isooctane alkyl
HO2hydroperoxyl radical
H2O2hydrogen peroxide
OHhydroxyl radical
Mthird body

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Figure 1. Structure body and mesh generation for the engine model: (A) STL model; (B) meshed model; (C) longitudinal section; (D) transverse section.
Figure 1. Structure body and mesh generation for the engine model: (A) STL model; (B) meshed model; (C) longitudinal section; (D) transverse section.
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Figure 2. Relative locations of port fuel injector, direct injector, and spark plug.
Figure 2. Relative locations of port fuel injector, direct injector, and spark plug.
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Figure 3. Engine test system.
Figure 3. Engine test system.
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Figure 4. Comparison of calculated and measured (a) cylinder pressures, (b) heat release rates (HRRs), and (c) global NOx emissions. TDC, top dead centre.
Figure 4. Comparison of calculated and measured (a) cylinder pressures, (b) heat release rates (HRRs), and (c) global NOx emissions. TDC, top dead centre.
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Figure 5. Cylinder pressure at different direct injection (DI) timings with variation of ammonia mass fraction (AMF): (a) DI timing = −105 °CA; (b) DI timing = 0 °CA; (c) DI timing = 40 °CA.
Figure 5. Cylinder pressure at different direct injection (DI) timings with variation of ammonia mass fraction (AMF): (a) DI timing = −105 °CA; (b) DI timing = 0 °CA; (c) DI timing = 40 °CA.
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Figure 6. Mass of OH radicals at different DI timings with variation of AMF: (a) DI timing = −105 °CA; (b) DI timing = 0 °CA; (c) DI timing = 40 °CA.
Figure 6. Mass of OH radicals at different DI timings with variation of AMF: (a) DI timing = −105 °CA; (b) DI timing = 0 °CA; (c) DI timing = 40 °CA.
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Figure 7. Mass of H2O2 radicals at different DI timings with variation of AMF: (a) DI timing = −105 °CA; (b) DI timing = 0 °CA; (c) DI timing = 40 °CA.
Figure 7. Mass of H2O2 radicals at different DI timings with variation of AMF: (a) DI timing = −105 °CA; (b) DI timing = 0 °CA; (c) DI timing = 40 °CA.
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Figure 8. Mass of HO2 radicals at different DI timings with variation of AMF: (a) DI timing = −105 °CA; (b) DI timing = 0 °CA; (c) DI timing = 40 °CA.
Figure 8. Mass of HO2 radicals at different DI timings with variation of AMF: (a) DI timing = −105 °CA; (b) DI timing = 0 °CA; (c) DI timing = 40 °CA.
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Figure 9. NO evolution with variation of AMF (DI timing = −105 °CA).
Figure 9. NO evolution with variation of AMF (DI timing = −105 °CA).
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Figure 10. NO evolution with variation of AMF (DI timing = 0 °CA).
Figure 10. NO evolution with variation of AMF (DI timing = 0 °CA).
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Figure 11. NO evolution with variation of AMF (DI timing = 40 °CA).
Figure 11. NO evolution with variation of AMF (DI timing = 40 °CA).
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Figure 12. UHC variation at different DI timings and AMF values.
Figure 12. UHC variation at different DI timings and AMF values.
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Figure 13. CO variation at different DI timings and AMF values.
Figure 13. CO variation at different DI timings and AMF values.
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Figure 14. Soot variation at different DI timings and AMF values.
Figure 14. Soot variation at different DI timings and AMF values.
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Figure 15. Contribution of ammonia.
Figure 15. Contribution of ammonia.
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Table
Table 1. Main technical parameters of the commercial engine.
Table 1. Main technical parameters of the commercial engine.
Engine TypeOrthostichous, Four Cylinder, Water Cooled, Combined Injection
Compression ratio9.6:1
Displacement2.0 L
Bore × stroke82.5 × 92.8 mm
Maximum power147 kW (5000–6000 rpm)
Maximum torque280 N·m (1800–5000 rpm)
Table
Table 2. Initial parameters and boundary conditions. DI, direct injection; PRF, primary reference fuel; AMF, ammonia mass fraction.
Table 2. Initial parameters and boundary conditions. DI, direct injection; PRF, primary reference fuel; AMF, ammonia mass fraction.
Engine speed1500 r/min
Temperature of cylinder head550 K
Temperature of piston600 K
Temperature of cylinder liner450 K
Injected mass of PRF 9044.87 mg
Injection timing of PRF 90−373 °CA
Injected mass of the aqueous solution of ammonia8.97 mg
DI timing of the aqueous solution of ammonia−105 °CA, 0 °CA, and 40 °CA
NH3 mass fraction in the aqueous solution of ammonia (AMF)0% (pure water), 10%, and 20%
Injection pressure of the aqueous solution of ammonia5 MPa
Intake manifold temperature/pressure313 K/0.1 MPa
Exhaust manifold temperature/pressure650 K/0.11 MPa
Intake valve open (IVO)−381 °CA
Intake valve closed (IVC)−120 °CA
Exhaust valve open (EVO)−566 °CA
Exhaust valve closed (EVC)−340 °CA
Global equivalence ratio1 (stoichiometric condition)
Ignition energy0.04 J
Ignition timing−13 °CA
Table
Table 3. Setting of the simulation cases and the legend nomenclature.
Table 3. Setting of the simulation cases and the legend nomenclature.
Original BaselineAMF = 0%AMF = 10%AMF = 20%
DI timingNull−105 °CA−105 °CA−105 °CA
0 °CA0 °CA0 °CA
40 °CA40 °CA40 °CA
Table
Table 4. Decrease of NO emissions with variation of DI timing and AMF based on original values.
Table 4. Decrease of NO emissions with variation of DI timing and AMF based on original values.
AMF = 0%AMF = 10%AMF = 20%
DI timing = −105°CA37.4%45.7%54.0%
DI timing = 0 °CA48.6%56.9%65.1%
DI timing = 40 °CA20.3%27.1%33.6%

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MDPI and ACS Style

He, F.; Yu, X.; Du, Y.; Shang, Z.; Guo, Z.; Li, G.; Li, D. Inner Selective Non-Catalytic Reduction Strategy for Nitrogen Oxides Abatement: Investigation of Ammonia Aqueous Solution Direct Injection with an SI Engine Model. Energies 2019, 12, 2742. https://doi.org/10.3390/en12142742

AMA Style

He F, Yu X, Du Y, Shang Z, Guo Z, Li G, Li D. Inner Selective Non-Catalytic Reduction Strategy for Nitrogen Oxides Abatement: Investigation of Ammonia Aqueous Solution Direct Injection with an SI Engine Model. Energies. 2019; 12(14):2742. https://doi.org/10.3390/en12142742

Chicago/Turabian Style

He, Fengshuo, Xiumin Yu, Yaodong Du, Zhen Shang, Zezhou Guo, Guanting Li, and Decheng Li. 2019. "Inner Selective Non-Catalytic Reduction Strategy for Nitrogen Oxides Abatement: Investigation of Ammonia Aqueous Solution Direct Injection with an SI Engine Model" Energies 12, no. 14: 2742. https://doi.org/10.3390/en12142742

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