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Article

Effect of Hydrogen-Rich Syngas Direct Injection on Combustion and Emissions in a Combined Fuel Injection—Spark-Ignition Engine

by
Zhen Shang
1,2,
Yao Sun
2,*,
Xiumin Yu
2,
Ling He
2 and
Luquan Ren
1
1
Key Laboratory of Bionic Engineering, Ministry of Education, Jilin University, Changchun 130022, China
2
State Key Laboratory of Automotive Simulation and Control, Jilin University, Changchun 130022, China
*
Author to whom correspondence should be addressed.
Sustainability 2023, 15(11), 8448; https://doi.org/10.3390/su15118448
Submission received: 17 April 2023 / Revised: 19 May 2023 / Accepted: 19 May 2023 / Published: 23 May 2023
(This article belongs to the Special Issue Emerging Research in Rotary Engines and Sustainability in Vehicle Engineering)
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Abstract

:
To utilize the high efficiency of gasoline direct injection (GDI) and solve the high particulate number (PN) issue, hydrogen-rich syngas has been adopted as a favorable sustainable fuel. This paper compares and analyzes the effects of the injection configurations (GDI, gasoline port injection combined with GDI (PGDI), and gasoline port injection combined with hydrogen-rich syngas direct injection (PSDI)) and fuel properties on combustion and emissions in a spark-ignition engine. The operational points were fixed at 1800 rpm with a 15% throttle position, and the excess air ratio was 1.1. The conclusions show that PSDI gained the highest maximum brake thermal efficiency (BTE) at the MBT point, and the maximum BTE for GDI was only 94% of that for PSDI. PSDI’s CoVIMEP decreased by 22% compared with GDI’s CoVIMEP. CO and HC emissions were reduced by approximately 78% and 60% from GDI to PSDI among all the spark timings, respectively, while PSDI emitted the highest NOX emissions. As for particulate emissions, PSDI emitted the highest nucleation-mode PN, while GDI emitted the lowest. However, the accumulation-mode PN emitted from PSDI was approximately 52% of that from PGDI and 5% of that from GDI. This study demonstrates the benefits of PSDI for sustainability in vehicle engineering.

1. Introduction

With the development of engine technologies, gasoline direct injection (GDI) and port fuel injection (PFI) have been widely used for modern spark-ignition engines. As direct fuel injection can be more accurately controlled both for quantity and timing, GDI generally provides better transient condition performance, which results in better fuel economy and lower CO2 emissions [1,2]. However, previous research has concluded that GDI emits more particulate emissions than PFI because the time for mixture forming is relatively short, and locally fuel-rich regions appear more [3,4].
It is important to recognize the connection between particulate emissions and sustainability as well as take steps to reduce emissions and promote sustainable practices due to their adverse impact on air quality, human health, and the environment [5]. Therefore, to make GDI engines conform to the sustainability of vehicle engineering, GDI combined with PFI seems to be a promising method to improve efficiency and simultaneously solve the emissions issue [6,7,8]. Kang et al. developed a single-cylinder, four-stroke engine that adopts one direct injection system combined with one port injector. The results showed that the engine load characteristics were widened compared with a conventional spark-ignition direct injection (SIDI) engine, and knock reduction and engine flexibility can also be found in a dual-fuel dual-injection engine [9]. Sun et al. investigated the particulate number (PN) reduction and size distribution in a combined dimethyl ether/gasoline injection SI engine. They concluded that by increasing the proportion of dimethyl ether direct injection, both the nucleation and accumulation modes of PN emissions drop remarkably [10].
On the other side, finding alternative fuels for internal combustion engines is also a feasible pathway for sustainable development to meet stringent emission regulations and solve the shortage of conventional fuel [11]. Synthesis gas (syngas) is considered an attractive substitute energy due to its abundant sources and clean combustion characteristics [12]. The feedstock for syngas can be biomass, coal, refinery coke, or even landfill waste, whilst the manufacturing methods include gasification, fuel reforming, and fermentation [13,14]. The combustible species of syngas are H2, CO, and CH4, and the inert diluents of syngas are mainly N2 and CO2. The high hydrogen content in syngas determines that syngas belongs to clean energy [15]. The production method affects the specific composition of syngas, for example, applying catalytic gasification technology to gasify biomass could yield a hydrogen-enriched synthetic gas with hydrogen and CO contents of up to 50% and 17% by volume [16]. Harun et al. reported that the CO contained in syngas could increase the knock limit, and the combustion duration was also prolonged [17]. Concerning hydrogen-rich syngas, the physicochemical characteristics of hydrogen can be inherited to some extent, while the sources of syngas are much more convenient than hydrogen [18,19]. Hydrogen has some excellent physicochemical characteristics, such as wide flammability, low minimum ignition energy, a high laminar burning velocity, and a small quenching distance [20]. Therefore, injecting syngas directly into a cylinder may have a better effect on reducing emissions than gasoline direct injection because of the fuel properties.
To figure out the environmental issues and sustainable development, the influences of syngas on gaseous emissions have been widely investigated [15]. Huang et al. studied how the ignition timing affects emissions from a syngas internal combustion engine containing hydrogen by using a spark plug reformer system [21]. They successfully developed a spark plug reformer system that can reduce power consumption and operate under a low operating temperature [22]. The experiment showed that when the spark timing was adjusted to the MBT, HC and NOX emissions decreased, while CO2 and CO emissions slightly increased with the use of syngas. Grzegorz et al. also concluded that hydrogen-rich syngas and high equivalence ratios cause a higher reaction temperature that favors NOX emissions [23]. Harun et al. compared the content ratio of hydrogen and CO in syngas and obtained that the emissions were greatly related to the syngas composition. In particular, the NO level with a H2/CO ratio of 2.36 was lower than that with a H2/CO ratio of 0.62 even though it had a high exit temperature and hydrogen content [24]. Similarly, Ouimette et al. reported a different NOX emission tendency of syngas in partially premixed combustion conditions. They indicated that NOX emissions remained stable for syngas mixtures with a H2/CO ratio of 0–1.3, whereas NOX emissions exhibited a clear downward trend with higher ratios (>1.3) [25].
There are few published papers that have studied the particulate matter (PM) in syngas combustion, but the effect of hydrogen on particulate emissions has been investigated. Singh A. P. et al. compared the PM emissions from hydrogen-, CNG-, HCNG-, gasoline-, and diesel-fueled engines. They reported that hydrogen emitted the lowest PN and the lowest amount of PM among the researched fuels. Moreover, hydrogen enrichment of CNG reduced the total PM emissions [26]. Zhao et al. analyzed PM emissions from a GDI engine using a hydrogen and gasoline mixture. The findings revealed that under a low load, blending 5% hydrogen into the stoichiometric mixture can lower the total PM mass and PM number by up to 90%, and a further reduction in the total mass to 95% as well as in the total number to 97% can be achieved with 10% hydrogen. Nevertheless, under a high load, although hydrogen addition decreased the number of smaller particles, it encouraged the generation of accumulation-mode particles [27].
Thus, in this study, to realize both high thermal efficiency and low engine emissions, the adoption of hydrogen-rich syngas direct injection in a combined fuel injection–SI engine was evaluated. Two sets of experiments were formulated. The first one was about the comparison between GDI and gasoline port injection combined with GDI (PGDI) and aimed to analyze the configuration characteristic of the combined injection system. The second set of experiments was about the comparison between PGDI and gasoline port injection combined with syngas direct injection (PSDI), aiming to further analyze the fuel properties of syngas. In addition, from our previous research, a comparison between the injection modes containing GDI, PGDI, and gasoline port injection combined with hydrogen direct injection was carried out, and the experiments showed that the combination of an injection mode with fuel had a great influence on engine behavior [28,29,30], which means this specific investigation on the combustion, gaseous emission, and PN emission characteristics of syngas, which have not been studied yet, is novel and will be useful to meet sustainable development requirements.

2. Materials and Methods

2.1. Experimental Setup

The prototype engine was an in-line four-cylinder water-cooled spark-ignition direct injection (SIDI) engine, which originally had two injection systems, one direct injection system, and one port injection system. The cylinder head was furnished with centrally mounted spark plugs and direct injectors situated between intake valves. Port injectors were arranged on intake manifolds. Table 1 lists the detailed specifications of the prototype engine. The injection timing and duration for both gasoline and syngas were controlled with a self-developed ECU that can also adjust the throttle position and ignition timing. The syngas used in this experiment was hydrogen-rich syngas with fixed 85% H2 and 15% CO by volume to eliminate interferences [31,32]. The specifications of the gasoline and syngas are shown in [28] and [33]. To maintain the operating state with a fixed excess air ratio (λ), the requested fuel distribution ratio was obtained through the precise monitoring of the airflow, syngas flow, and gasoline flow. Moreover, due to the wide flammability of hydrogen, a flame arrestor was installed within the hydrogen supply line to avoid backfire. Figure 1 illustrates the overall schematic layout of the experimental system.
During the experiments, the engine’s speed and torque were measured using an ECD CW160 that was controlled with an FST-OPEN system. A GU13Z-24 piezoelectric pressure sensor was used to measure the cylinder pressure, and the crank angle was measured with a Kistler-2614B4 encoder. Both sets of data were transmitted to a combustion analyzer to calculate the real-time cylinder pressure and analyze the combustion process through the combustion analysis software (DS 0928). The excess air ratio was recorded with a Meter LA4 lambda sensor, and a wideband oxygen transducer was mounted onto the exhaust pipe. The syngas mass flow was monitored with a DMF-1-1 AB gas flow meter. In addition, the regular gas emissions could be measured simultaneously with a DiCom 4000 analyzer. Particulate emissions were recorded using a DMS500, which can measure the particulate number and provide the PN size distribution. The specific information on the testing instruments including the measuring error is shown in Table 2.

2.2. Experimental Procedures

In all the experiments, the engine speed was constant at 1800 rpm, representing a normal urban situation. Some research studies have indicated that different injection modes could affect volumetric efficiency [34]. To highlight the influence of volumetric efficiency, a low engine load associated with a small throttle position was chosen. Therefore, the throttle position was fixed at 15% for all the experiments, and other loads will be investigated in future work. The port fuel injection was aimed to form a homogenous mixture, and the port injection time was set at 300 crank angle degrees before the top dead center (CAD BTDC). Both the syngas and gasoline direct injection pressures were set at 3 MPa to unify the standards. In previous studies, when hydrogen was injected at 100 CAD BTDC, the engine exhibited the best efficiency and the highest power output, so the direct injection timings in this study were set at 100 CAD BTDC (both for syngas and gasoline) [35]. As low-temperature combustion achieved via lean-burn has been proven to be beneficial for increasing engine efficiency and decreasing emissions [36,37], and syngas can extend the lean-burn limit, the experiments were conducted under lean-burn conditions. The λ was fixed at 1.1, and the definition of λ is shown as follows:
λ = V a i r ρ a i r m s A F s + m g A F g  
In Equation (1), V a i r represents the air volumetric flow rate, and ρ a i r represents the density of air. m s and m g denote the measured mass flow rates of syngas and gasoline. Especially for the PDI mode, m g equals the total gasoline mass flow rate including both direct injection and port injection. A F s and A F g are equal to 29.52 and 14.6 as the stoichiometric air–fuel ratios of syngas and gasoline, respectively.
The definition of the fuel distribution ratio is indicated in Equation (2) representing the energy ratio:
Φ D = q D q D + q P  
In Equation (2), Φ D denotes the fuel distribution ratio, q D and q P represent the heat released by the direct injection fuel (the gasoline direct injection portion in PGDI and that of syngas in PSDI) and port injection fuel, respectively. The heat is calculated from the mass flow rate and the low heating value (LHV). As the onboard syngas production amount was limited, the direct injection portion was regarded as an improver to fit the practical application [38]. Therefore, the Φ D for the PGDI mode was fixed at 20%, while the PSDI mode had a lower Φ D of 10%.
To find the effect on the combustion and emissions characteristics at various sparking timings, a range of spark timings from 10 CAD BTDC to 30 CAD BTDC were employed. The combustion parameters were measured and averaged in 200 continuous cycles at all test points. Concretely, the cylinder pressure, brake thermal efficiency (BTE), combustion durations (CA 0–10 and CA 10–90), indicated mean effective pressure (IMEP), and coefficient of variation in IMEP (CoVIMEP) were measured to analyze the combustion process. Moreover, the CO, HC, NOX, and PN emissions were recorded in the experiments to study the emission characteristics. Notably, the comparisons of the three injection modes are novel and will be useful for future vehicle engineering sustainability.

3. Results and Discussion

3.1. Cylinder Pressure and Brake Thermal Efficiency

Figure 2 and Figure 3 plot the in-cylinder pressure for the three kinds of injection modes with spark timings at 10 CAD BTDC and 25 CAD BTDC. The cylinder pressures for PSDI show the highest cylinder pressure, while GDI presents the lowest value in both figures. Firstly, investigating the injection configuration and then analyzing the fuel properties indicated some detailed effects among the three injection modes. Port fuel injection has more time to form a homogenous mixture beneficially, and the direct injection portion can achieve stable and reliable ignition, so the combustion efficiency and cylinder pressure can be increased with combined fuel injection. This conclusion is similar to that in [39], which mainly focuses on fuel consumption and half-load performance. Furthermore, as syngas has a high laminar flame speed that can enhance the constant volume combustion degree, and its small quenching distance also facilitates more complete combustion, the cylinder pressure of PSDI performs higher than that of PGDI.
With 2 spark timings, the relevant crank angles for the maximum cylinder pressure of PSDI were only 16 CAD ATDC and 1 CAD ATDC, respectively. The relevant phasing was much more advanced than that of the GDI and PGDI modes, mainly because of the dramatically shortened combustion period. As syngas has a high laminar burning velocity, the combustion is more concentrated in the top dead center (TDC) with a specific spark timing. The cylinder pressure is an integrated result of the piston motion and combustion process, and the piston motion produces the highest pressure around the TDC (due to the smallest displacement). The concentrated combustion moves the highest cylinder pressure closer to the TDC, which enlarges the integrated pressure. Furthermore, advancing ignition lets more fuel burn before the TDC, and the accumulated heat before the TDC gradually increases, which results in higher in-cylinder pressure. However, the combustion deteriorates, as the relevant crank angle for the highest cylinder pressure is too early with an over-advanced spark timing.
Figure 4 plots the brake thermal efficiency (BTE) at various spark timings for three kinds of injection modes. As the minimum spark advance for best torque (MBT) for GDI and PGDI is 20 CAD BTDC, while the MBT for PSDI is only 10 CAD BTDC, the investigated ranges of ignition timings had a slight difference. When the spark timing was set at the MBT, PSDI demonstrated the highest maximum BTE (30.3%), while GDI showed the least maximum value (28.7%), and the maximum BTE of PGDI was 29.8%. The maximum BTE increased by 1.6% from GDI to PSDI. PGDI can form a more homogeneous mixture, producing complete combustion and higher BTE. As syngas has high diffusive efficiency and low ignition energy, the homogenous condition was further enhanced, and the requirement for combustion declined. These factors are all beneficial for complete combustion, which is critically beneficial for BTE. Moreover, a high laminar burning velocity shortens the combustion period and reduces heat transfer loss. As such, PSDI has higher BTE than GDI because of more complete combustion, higher combustion efficiency, and less heat transfer loss.
Figure 4 also shows that the BTE first rises and then descends with an advancing spark timing. This is because an over-advanced spark timing makes more fuel burn during the compression stroke which produces more negative compression work and decreases the BTE. Comparatively, over-retarding the spark timing would enlarge the extent of post-combustion, and more fuel would burn during the expansion stroke, resulting in lower BTE. It is worth noting that when the spark advance angle was larger than 15 CAD, the BTE of PSDI decreased quickly and was even worse than that of GDI. This is because the combustion duration for PSDI is relatively short, and over-advancing ignition causes most of the combustion to be completed before the TDC, and the negative compression work increases. Subsequently, the BTE for PSDI declined dramatically. As the combustion speeds are lower in GDI and PGDI, the influences by over-advancing ignition are relatively small for these two modes. Thus, PSDI is more sensitive to spark timings because of the high flame speed.
Figure 5 shows the cylinder temperature at the exhaust valve opening (TEVO) versus the spark timings for the three kinds of injection modes. The TEVO reflects the engine post-combustion and exhaust loss to some extent [40]. The cam phasing was fixed just as the original engine and the exhaust valve opened at 26 CAD before the bottom dead center (BBDC). The TEVOs for the GDI and PGDI modes are relatively similar, and the TEVO for the PSDI mode is substantially higher than those for the other modes. The exhaust temperature for PSDI shows the highest value because of the fast burning velocity and higher maximum cylinder pressure. The TEVO mainly affected the emissions characteristics, and the details will be discussed in Section 3.3.

3.2. Combustion Analysis

Figure 6 plots the flame development duration (0–10% mass fraction burned; CA 0–10) at various spark timings for the 3 kinds of injection modes, and Figure 7 plots the flame propagation duration (10%–90% mass fraction burned; CA 10–90). PGDI shows a shorter duration for both CA 0–10 and CA 10–90 than GDI, and PSDI demonstrates the shortest durations for both parts. The combined injection mode can form a more stratified mixture than the pure GDI mode, which eases the formation of the flame kernel and accelerate the whole combustion period, so PGDI indicates shorter combustion durations. According to previous studies, adding hydrogen to methane and ethanol stimulates the formation of O, OH, and H radicals, which are kinds of improvers for chain reactions [41,42]. The syngas used in this investigation was hydrogen-rich, so it inherited some hydrogen characteristics, and gasoline is a kind of hydrocarbon fuel that is chemically similar to ethanol and methane. Thus, the formation of radicals stimulated via syngas accelerates combustion and shortens the combustion period. A shorter CA 0–10 means more stable combustion, while a shorter CA 10–90 means the combustion process is closer to the constant volume process, allowing higher thermal efficiency [43]. Hence, it is further certified that PSDI has the most stable combustion and the highest thermal efficiency among the three injection modes. On the other hand, by advancing the ignition timing, CA 0–10 was prolonged while CA 10–90 was shortened for all three injection modes. Advancing ignition deteriorates the initial condition for forming the flame kernel, and CA 0–10 is prolonged. Retarding ignition expands the degree of post-combustion, and the combustion at this stage is mainly diffusion combustion with a low burning rate. Thus, the CA 10–90 duration is extended by retarding the ignition timing.
Figure 8 plots the coefficients of variation (CoVs) in the IMEP at various spark timings for the three kinds of injection modes. The CoVIMEP of GDI is dramatically higher than those of the other two modes, and it is very sensitive to spark timings. Specifically, the minimum CoVIMEP of PSDI decreases by 22% from the minimum CoVIMEP of GDI. Many investigations have indicated that a short combustion duration helps to ease an engine’s cyclic variations [44]. It is seen in Figure 6 and Figure 7 that the combustion duration of GDI is obviously long, leading to a high CoVIMEP. Figure 8 also indicates that the CoVIMEP reaches its lowest value at around the MBT point.

3.3. Gaseous Emissions and PN Emissions

Figure 9 plots CO emission at various spark timings for the three kinds of injection modes. GDI emits the highest CO emission, while PSDI emits the least. CO emissions were reduced by approximately 78% from GDI to PSDI among the whole range of spark timings. However, a 15% volumetric fraction of the syngas used in this experiment was CO, and the CO emission still shows the least value for PSDI, which further certifies that PSDI is beneficial for complete combustion and shows better stability. Ji C. et al. concluded that adjusting the spark timing has no clear effect on the CO emission of a hybrid hydrogen–gasoline engine [45], which agrees with the PSDI profile. CO emission decreased by retarding ignition for the GDI and PGDI modes, as the prolonged post-combustion induced by retarding ignition enhances the oxidation of CO.
As is shown in Figure 10, GDI emits the highest HC emission, and PGDI and PSDI only emit small amounts. HC emissions were reduced by approximately 60% from GDI to PSDI with a 20 CAD BTDC spark timing. This is because the combined injection mode improves combustion completeness, which reduces the sources of HCs. For the GDI mode, HC emission decreased by retarding ignition, the reason for which could be ascribed to the enhanced oxidizing process caused by prolonged post-combustion and increased TEVO.
Figure 11 plots the NOX emissions at various spark timings for the three kinds of injection modes. PSDI produced the highest NOX emission, whereas GDI produced the lowest NOX emission. Specifically, the NOX emission from GDI was 44% and 32% of that of PGDI and PSDI, respectively. The main factors affecting NOX emissions include the oxygen fraction, cylinder temperature, and reserved time for high-temperature reactions [46]. As the data in Figure 11 show, PSDI still has a high NOX emission problem. However, as syngas direct injection avails stable combustion, lean-burn combustion and exhaust gas recirculation (EGR) technologies could be used to reduce NOX emissions without causing much damage to the engine performance according to [47]. Figure 11 also indicates that retarding ignition linearly reduces NOX emissions. This is because retarding ignition decreases the maximum cylinder temperature, which is a critical factor for NOX emission.
Particulate emissions are a common issue for SIDI engines, and SIDI engines always have high particulate numbers relative to diesel engines, so the particulate emission numbers will be focused on herein. Figure 12 plots the total nucleation-mode PNs at various spark timings for the three kinds of injection modes, and Figure 13 shows the total accumulation-mode PNs for the three kinds of injection modes. Particles in nucleation mode are typically composed of volatile organic and sulfur compounds that form during exhaust dilution and cooling. Meanwhile, particles in accumulation mode are mainly made up of carbonaceous agglomerates and associated adsorbed materials [48,49,50].
Regarding the nucleation-mode PN, PSDI generally emits the highest value while GDI emits the lowest value. The nucleation-mode PN for GDI is only 45% of that for PSDI at a 20 CAD BTDC spark timing. As nucleation-mode particles are mainly from exhaust dilution and cooling, a higher exhaust temperature will enhance the nucleation process and result in more nucleation-mode particles. From the results shown in Figure 5, the TEVO of PSDI is the highest among the three injection modes, which is conducive to the formation of nucleation-mode particles. The three injection modes present different ignition characteristics in Figure 12, and GDI emits the lowest nucleation-mode PN at the MBT point, while PGDI and PSDI show slight variations with the spark timings. This is ascribed to the relatively high exhaust temperature and low unburned hydrocarbons in PSDI and PGDI, which decrease the propensity to oxidize the particles. Consequently, the PGDI and PSDI modes respond less sensitively to spark timings. Although PSDI increases the nucleation-mode PN, improving the dilution condition in the exhaust pipe and eliminating temperature differences will dramatically reduce the nucleation-mode PN.
Regarding the accumulation-mode PN, GDI shows the highest value, and PSDI indicates the lowest value. The accumulation-mode PN of PSDI is approximately 52% of PGDI’s and 5% of GDI’s, respectively. Accumulation particles are mainly formed during the combustion process of an inhomogeneous mixture [51]. PGDI dramatically enhances the homogenous situation in a cylinder via the port fuel injection, and the accumulation particle number obviously decreases from that of GDI. Particle growth and augmentation are mainly enacted through H atom loss and continue through the addition of the acetylene (HACA) mechanism [52]. Adding syngas increases the H atom amount in the cylinder, and the HACA mechanism is suppressed. Therefore, PSDI further reduces the accumulation-mode PN compared with PGDI.

4. Conclusions

This paper experimentally investigated the effect of hydrogen-rich syngas direct injection on combustion and emissions in a combined fuel injection—spark-ignition engine. Direct comparisons between the GDI, PGDI, and PSDI modes with cylinder pressure, BTE, CA0–10, CA10–90, CoVIMEP, CO, HC, NOX, and PN emissions versus spark timing were performed to analyze the effects of the injection configurations and the fuel properties to meet the requirements of sustainable development. The main conclusions are listed as follows:
  • When the spark timing was fixed at the MBT for the three injection modes, PSDI gained the highest maximum BTE, while the maximum BTE of GDI was only 94% of PSDI’s. In addition, the BTE of PSDI was much more sensitive than that of the other two modes due to the high burning rate of syngas.
  • PSDI performed the shortest durations, and GDI showed the longest duration for both CA0–10 and CA 10–90. The CoVIMEP of GDI was dramatically higher than that of the other two modes, and the variations were very sensitive to spark timings in GDI. The minimum CoVIMEP of PSDI decreased by 22% from the minimum value of GDI.
  • CO emissions were reduced by approximately 78% from GDI to PSDI among the whole range of spark timings, and HC emissions were reduced by approximately 60% from GDI to PSDI. However, PSDI showed the highest NOX emissions, and GDI showed the lowest value. Specifically, the NOX emissions from GDI were 44% and 32% of that from PGDI and PSDI, respectively. Retarding ignition linearly reduced NOX emissions for the three injection modes.
  • PSDI generally emitted the highest nucleation PN while GDI emitted the lowest. The nucleation-mode PN for GDI was only 45% of that for PSDI at a 20 CAD BTDC spark timing. Improving the exhaust conditions and eliminating temperature differences will dramatically reduce the nucleation-mode PN.
  • GDI showed the highest accumulation-mode PN and PSDI indicated the lowest. The accumulation-mode PN for PSDI was approximately 52% of that for PGDI and only 5% of that for GDI. The small amount of accumulation-mode particles certifies the effect of hydrogen-rich syngas on reducing particles. Thus, PSDI is a feasible method to solve the high particulate emission issue in DISI engines and also improve engine performance.
In conclusion, the method of PSDI can exhibit the dual advantages of combined injection and syngas fuel properties to achieve high BTE and low CO, HC, and particulate emissions. In future research, we may develop a special exhaust after-treatment system for syngas or investigate the performance of syngas direct injection engines under various load conditions so as to better adapt to the sustainable development goal of vehicles.

Author Contributions

Conceptualization, Y.S. and X.Y.; validation, L.H.; formal analysis, Y.S.; investigation, Z.S. and Y.S.; resources, X.Y.; data curation, Z.S. and Y.S.; writing—original draft preparation, Y.S.; writing—review and editing, Z.S.; supervision, X.Y.; project administration, L.R.; funding acquisition, L.R. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China (NSFC, 62103160), the Jilin Province Science and Technology Development Plan Project (no. 20210508058RQ), and the Dingxin Scholar Support Program of Jilin University (no. BD0097).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy restrictions.

Conflicts of Interest

The authors declare no conflict of interest.

Abbreviations

SI, spark ignition; GDI, gasoline direct injection; PGDI, gasoline port injection combined with GDI; PSDI, gasoline port injection combined with hydrogen-rich syngas direct injection; λ, excess air ratio; Φ_D, fuel distribution ratio; BTE, brake thermal efficiency; CA 0–10, flame development duration; CA 10–90, flame propagation duration; IMEP, indicated mean effective pressure; CoVIMEP, coefficient of variation in IMEP; TEVO, cylinder temperature at exhaust valve opening; MBT, minimum spark advance for best torque; TDC, top dead center; BDC, bottom dead center; PN, particulate number; PM, particulate matter.

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Figure 1. Schematic layout of the experimental system.
Figure 1. Schematic layout of the experimental system.
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Figure 2. In-cylinder pressure. Spark timing set at 10 CAD BTDC for 3 kinds of injection modes.
Figure 2. In-cylinder pressure. Spark timing set at 10 CAD BTDC for 3 kinds of injection modes.
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Figure 3. In-cylinder pressure. Spark timing set at 25 CAD BTDC for 3 kinds of injection modes.
Figure 3. In-cylinder pressure. Spark timing set at 25 CAD BTDC for 3 kinds of injection modes.
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Figure 4. BTE versus spark timings for three kinds of injection modes.
Figure 4. BTE versus spark timings for three kinds of injection modes.
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Figure 5. TEVO versus spark timings for three kinds of injection modes.
Figure 5. TEVO versus spark timings for three kinds of injection modes.
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Figure 6. CA 0–10 versus spark timings for three kinds of injection modes.
Figure 6. CA 0–10 versus spark timings for three kinds of injection modes.
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Figure 7. CA 10–90 versus spark timings for three kinds of injection modes.
Figure 7. CA 10–90 versus spark timings for three kinds of injection modes.
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Figure 8. CoVIMEP versus spark timings for three kinds of injection modes.
Figure 8. CoVIMEP versus spark timings for three kinds of injection modes.
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Figure 9. CO emissions versus spark timings for three kinds of injection modes.
Figure 9. CO emissions versus spark timings for three kinds of injection modes.
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Figure 10. HC emissions versus spark timings for three kinds of injection modes.
Figure 10. HC emissions versus spark timings for three kinds of injection modes.
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Figure 11. NOX emissions versus spark timings for three kinds of injection modes.
Figure 11. NOX emissions versus spark timings for three kinds of injection modes.
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Figure 12. Total nucleation-mode PNs versus spark timings for three kinds of injection modes.
Figure 12. Total nucleation-mode PNs versus spark timings for three kinds of injection modes.
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Figure 13. Total accumulation-mode PNs versus spark timings for three kinds of injection modes.
Figure 13. Total accumulation-mode PNs versus spark timings for three kinds of injection modes.
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Table
Table 1. Original engine specifications.
Table 1. Original engine specifications.
ParameterUnitValue
Compression ratio-9.6
Total displacementL1.984
Strokemm92.8
Boremm82.5
Rated torqueNm, rpm350, 1500–4500
Rated powerkW, rpm160, 4500–6200
Table
Table 2. Information on testing instruments.
Table 2. Information on testing instruments.
ApparatusParameterManufacturerTypeUncertainty
DynamometerEngine speedLY NanfengCW160≤±1 rpm
Torque≤±0.28 Nm
Pressure sensorCylinder pressureAVLGU 13Z-24≤±0.3 bar
Lambda analyzerExcess air ratioETASLAMBDA LA4≤±0.1
Gas flowmeterSyngas quantityBeijing SINCERITYDMF-1-1 AB≤±0.01 g/s
Fuel flowmeterGasoline quantityONO SOKKIDF-2420≤±0.01 g/s
Emission analyzerCOAVLDiCom 4000≤±0.01%
HC≤±30 ppm
NOX≤±20 ppm
Fast particulate analyzerParticulate emissionsCAMBUSTIONDMS500≤±1%
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MDPI and ACS Style

Shang, Z.; Sun, Y.; Yu, X.; He, L.; Ren, L. Effect of Hydrogen-Rich Syngas Direct Injection on Combustion and Emissions in a Combined Fuel Injection—Spark-Ignition Engine. Sustainability 2023, 15, 8448. https://doi.org/10.3390/su15118448

AMA Style

Shang Z, Sun Y, Yu X, He L, Ren L. Effect of Hydrogen-Rich Syngas Direct Injection on Combustion and Emissions in a Combined Fuel Injection—Spark-Ignition Engine. Sustainability. 2023; 15(11):8448. https://doi.org/10.3390/su15118448

Chicago/Turabian Style

Shang, Zhen, Yao Sun, Xiumin Yu, Ling He, and Luquan Ren. 2023. "Effect of Hydrogen-Rich Syngas Direct Injection on Combustion and Emissions in a Combined Fuel Injection—Spark-Ignition Engine" Sustainability 15, no. 11: 8448. https://doi.org/10.3390/su15118448

APA Style

Shang, Z., Sun, Y., Yu, X., He, L., & Ren, L. (2023). Effect of Hydrogen-Rich Syngas Direct Injection on Combustion and Emissions in a Combined Fuel Injection—Spark-Ignition Engine. Sustainability, 15(11), 8448. https://doi.org/10.3390/su15118448

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