Lean-burn Conditions Research Articles

Effect of hydrogen addition on the combustion and emission characteristics of methane under gas turbine relevant operating condition

The influence of hydrogen addition (0–100%) on the combustion and emission characteristics (NO and CO formation) of laminar-premixed methane flame under gas turbine relevant operating conditions was numerically studied. The PREMIX code of ANSYS CHEMKIN-PRO and the GRI-Mech 3.0 were utilized. The study of the effect of increasing hydrogen content in the methane-hydrogen mixtures on combustion and emissions at T = 298 K, P = 1 atm can provide a reference for our subsequent research on gas turbine conditions (T = 723 K, P = 16.5 atm). The LBV (laminar burning velocity) and AFT (adiabatic flame temperature) with different hydrogen contents (XH2=0–100%) and equivalence ratio (Φ = 0.6–1.4) were investigated. In addition, under gas turbine relevant lean burning conditions (Φ = 0.6, 0.8), the effect of hydrogen addition on the NO and CO emissions were investigated. The rate and sensitivity coefficients of NO/CO production were also examined. The results show that the LBV and AFT increase with the hydrogen content. Both the mole fraction of H, O and OH radicals and the flame temperature were observed to increase with the hydrogen content. Furthermore, the hydrogen addition can significantly increase the NO emissions and on the other hand suppress the CO formation. Reducing the equivalence ratio (from 1.2 to 0.6) can significantly reduce the NO emission. The addition of hydrogen can also increase the combustion stability of methane fuel under fuel-lean conditions. This is a good hint for gas turbine device to reduce NO emissions at fuel-lean side (Φ < 1).

Ignition timing effect on the combustion performance of hydrogen addition in methane fermentation gas in a local energy system

Nowadays, the reduction in carbon emission becomes the big issue in the world. In order to achieve the target of “carbon neutral” in the middle of 21st century, a regional energy system is designed to develop a carbon recycle system with the help of fermented gaseous fuels for electric power generation. Hydrogen (H2) addition is widely used for methane (CH4) combustion to improve the engine efficiency. However, less attention was paid on the various ignition timing for the maximum brake torque (MBT) and brake thermal efficiency (BTE) at a certain power output. In order to check the ignition timing effect on CH4 combustion with H2 addition, experiments were performed in a spark ignition engine with engine speed fixed on 1500 revolutions per minute (rpm). Firstly, CH4 was only used for combustion with excess air ratio (λ) changing from 1.01 to 1.42. Then, H2 was added with volume percentage varying from 10% to 50%. Among these discussions, torque, brake mean effective pressure (BMEP), BTE and brake specific fuel consumption (BSFC) were evaluated. Based on the results, high efficiency can be achieved by advancing the ignition timing when CH4 only at larger λ. When H2 added, the ignition timing should be retarded to obtain higher BTE from 10 % to 50 % H2 addition. Under the lean-burn condition, through delaying the ignition timing at −15° CA TDC, BTE of 50% H2 addition reaches to 22%, which is even higher than that of CH4 only combustion at stoichiometric condition. Furthermore, working and optimal regions for the co-combustion of H2 and CH4 are mapped under various conditions.

Lean Burn Flame Kernel Characterization for Different Spark Plug Designs and Orientations in an Optical GDI Engine

Lean burn spark ignition (SI) engines represent an effective solution for improving fuel economy and reducing exhaust emissions and can be implemented both in conventional and hybrid powertrains. On the other hand, lean operation increases cyclic variability with negative impact on power output, engine efficiency, roughness, and operating stability. Although this phenomenon has been widely investigated, the effects of flow field on the inception and development of flames in direct injection spark ignition (DISI) engines under lean burn conditions is not yet completely understood. In particular, the effect of spark plug geometry and electrode orientation with respect to tumble motion has been minimally investigated. For these reasons, two different spark-plug geometries (i.e., single- and double-ground electrode) and three different orientations (i.e., cross-, counter-, and uni-flow with respect to the direction of tumble motion) were investigated in an optically accessible DISI engine for understanding their influence on the initial phase of combustion. The relative air–fuel ratio (AFRrel) was changed from stoichiometric to lean burn (1.00 to 1.30) for different spark timings around the maximum brake torque setting at fixed engine speed (2000 rpm). An image processing procedure was developed for evaluating the morphological parameters of flame kernels and studying the effects of spark plug design on engine operating stability. With a focus on the correlation between the position where ignition occurs with the subsequent locations of the flame kernel during the first phases of the combustion process, the analysis allowed the gathering of a better understanding of the influence that the electrodes’ geometries and orientation can have on the first stages of combustion development.

A Transition of Ignition Kernel Delay Time at the Early Stages of Lean Premixed n-Butane/Air Turbulent Spherical Flame Propagation

This paper explores the effects of root-mean-square turbulence fluctuation velocity (u′) and ignition energy (Eig) on an ignition kernel delay time (τdelay) of lean premixed n-butane/air spherical flames with an effective Lewis number Le ≈ 2.1 &gt;&gt; 1. Experiments are conducted in a dual-chamber, fan-stirred cruciform burner capable of generating near-isotropic turbulence with negligible mean velocities using a pair of cantilevered electrodes with sharp ends at a fixed spark gap of 2 mm. τdelay is determined at a critical flame radius with a minimum flame speed during the early stages of laminar and turbulent flame propagation. Laminar and turbulent minimum ignition energies (MIEL and MIET) are measured at 50% ignitability, where MIEL = 3.4 mJ and the increasing slopes of MIET with u′ change from gradual to drastic when u′ &gt; 0.92 m/s (MIE transition). In quiescence, a transition of τdelay is observed, where the decrement of τdelay becomes rapid (modest) when Eig is less (greater) than MIEL. For turbulent cases, when applying Eig ≈ MIET, the reverse trend of MIE transition is found for τdelay versus u′ results with the same critical u′ ≈ 0.92 m/s. These results indicated that the increasing u′ could reduce τdelay on the one hand, but require higher Eig (or MIET) on the other hand. Moreover, the rising of Eig in a specific range, where Eig ≤ MIE, could shorten τdelay, but less contribution as Eig &gt; MIE. These results may play an important role to achieve optimal combustion phases and design an effective ignition system on spark ignition engines operated under lean-burn turbulent conditions.

LFG 엔진의 희박 과급 연소 조건에서 화염 속도 측정 및 계산

In order not to release Landfill gas (LFG) having a high global warming potential into the atmosphere and to burn in an internal combustion engine for power generation, a study was conducted to measure and calculate flame speed under turbocharged and lean burn conditions of spark ignition engine. By changing the ratio between methane and carbon dioxide, which are the main components of LFG, experiments were conducted to measure the flame speed using a constant volume combustion chamber. Also comparative analysis was performed with data obtained using CHEMKIN library with GRI 3.0 mechanisms. In addition, using the data obtained through numerical analysis the correlations were derived to calculate the flame speed as a function of equivalence ratio. This study concludes that the overall trend of LFG flame speed is in good agreement between the experimental and calculated results. Using the correlated equation derived from the results of this study, it is possible to estimate the flame speed of LFG under turbocharged and lean burn of spark ignition engine.

Metal–Support Interactions within a Dual-Site Pd/YMn2O5 Catalyst during CH4 Combustion

Catalytic combustion is a promising technology for removing unburnt CH4 from natural gas vehicle exhaust gas under lean-burn conditions. Supported Pd catalysts are widely applied and studied for use in CH4 oxidation at <500–550 °C, with their activities significantly affected by the interactions between Pd and the support, depending on the dispersion, Pd valence state, and properties of the support. However, whether metal–support interactions are favorable in catalytic CH4 oxidation is unclear. We therefore used YMn2O5 as a catalytically active support to prepare a dual-site catalyst, Pd/YMn2O5, which shows high CH4 catalytic activities in dry and wet atmospheres. Experimental and density functional theory studies reveal that the CH4 adsorption and lattice oxygen activity of the support are significantly enhanced due to the interactions between PdOx and YMn2O5. In situ X-ray photoelectron spectroscopy shows that Pdx+ (x = 2 and 4) and Mnx+ (x = 3 and 4) species undergo changes during CH4 oxidation. The PdOx sites are the main active sites, as the CH4 activation barrier is much lower than those at other sites. YMn2O5 and PdOx participate in CH4 activation and oxidation via active oxygen transfer.

Axial Turbine Turbocharger for Charging a Lean-Burn Gasoline Engine

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;A single-stage turbocharger turbine is developed with the objective of enabling a gasoline spark-ignition engine to operate under lean-burn conditions with an air-to-fuel ratio of &lt;b&gt;&lt;i&gt;λ&lt;/i&gt;&lt;/b&gt;=2 in the range of the Worldwide Harmonized Light-Duty Vehicles Test Cycle. For this purpose, extensive 1-D engine simulations are performed using a combination of a simple compressor and simple turbine model as well as a combination of the stock compressor and a simple turbine model. The results show that an isentropic turbine efficiency of more than 70% over a wide operating range is required for the desired engine operation - especially with regard to the low-end-torque. Based on the crank-angle-resolved engine simulation data, turbine requirements are determined. Their evaluation shows that an axial turbine is a reasonable alternative to conventional radial turbines for this application. Next, a preliminary axial turbine is designed using 1-D/2-D design approaches. Then, the corresponding performance map is calculated by 3-D CFD simulations showing isentropic total-to-static turbine efficiencies of up to 77% over a wide operating range. Ultimately, the derived turbine performance map is implemented into the 1-D engine model and the valve train settings are optimized for this configuration to enhance the lean-burn performance further. The simulation results show a significantly extended &lt;i&gt;λ&lt;/i&gt;=2 operating range in comparison to the stock turbine.&lt;/div&gt;&lt;/div&gt;

Chemical kinetic investigation on NOx emission of SI engine fueled with gasoline-ethanol fuel blends

Understanding the nitrogen oxide (NOx) formation chemical kinetic mechanism and analyzing the effect of relevant influence parameters are the effective strategy for NOx emission control. Based on the essential role of ethanol-gasoline blends among oxygenate alternative fuel, the experiments in a GDI (gasoline direct injection) SI (spark ignition) engine and the chemical kinetic simulation were carried out. According to the validated model, seven NO contributing reactions and three reaction pathways were observed. Besides the thermal NO formation pathway, two other pathways with N2O and NNH through NH-HNO-NO have nonnegligible places in the high engine speed condition. As for the parameters, initial temperature aggravates NO emission, initial pressure and ethanol fraction inhibit NO, which influence it through thermal NO pathway and have slight impact on the other two pathways. While with the increase of equivalence ratio (ER) from 0.5 to 1.0, ER promotes first and then resists NO formation, getting highest emission when ER equals to 0.85. In a lean burn condition, the thermal pathway is highly inhibited and the N2O pathway is sharply accelerated. Through current work, NOx producing mechanism under high-speed condition is investigated comprehensively, which not only completes the total NO formation pathways from atmospheric N2 but also provides reference for the designing and modification of low harmful NOx emitting gasoline-ethanol engines.

A simple model catalyst study to distinguish the roles of different oxygen species in propane and soot combustion

It is important yet difficult to distinguish the specific roles of superficial Oxn- and interfacial lattice oxygen in catalytic combustion, especially over catalysts consisting of reducible metal oxides. In this study, based on the comparison of two natural counterparts with similar structure — CeO2 (an Oxn- generator) and Pr6O11 (a lattice oxygen contributor), it is suggested that the catalytic combustion of propane under lean-burn conditions followed a typical Mars-van Krevelen mechanism, in which catalyst lattice oxygen represented the dominant reactive phases while superficial Oxn- played negligible roles. As for soot combustion, adsorbed Oxn- represented more sustainable oxidants than lattice oxygen (drained easily at the beginning of the reactions). Such a comparison is readily achieved and widely applicable, which may shed light on the identification of dominant reactive phases for various oxidation reactions over oxide-based catalysts.

Effect of Ignition Energy and Hydrogen Addition on Laminar Flame Speed, Ignition Delay Time, and Flame Rising Time of Lean Methane/Air Mixtures

A series of experiments were performed to investigate the effect of ignition energy (Eig) and hydrogen addition on the laminar burning velocity (Su0), ignition delay time (tdelay), and flame rising time (trising) of lean methane−air mixtures. The mixtures at three different equivalence ratios (ϕ) of 0.6, 0.7, and 0.8 with varying hydrogen volume fractions from 0 to 50% were centrally ignited in a constant volume combustion chamber by a pair of pin-to-pin electrodes at a spark gap of 2.0 mm. In situ ignition energy (Eig ∼2.4 mJ ÷ 58 mJ) was calculated by integration of the product of current and voltage between positive and negative electrodes. The result revealed that the Su0 value increases non-linearly with increasing hydrogen fraction at three equivalence ratios of 0.6, 0.7, and 0.8, by which the increasing slope of Su0 changes from gradual to drastic when the hydrogen fraction is greater than 20%. tdelay and trising decrease quickly with increasing hydrogen fraction; however, trising drops faster than tdelay at ϕ = 0.6 and 0.7, and the reverse is true at ϕ = 0.8. Furthermore, tdelay transition is observed when Eig &gt; Eig,critical, by which tdelay drastically drops in the pre-transition and gradually decreases in the post-transition. These results may be relevant to spark ignition engines operated under lean-burn conditions.

Kinetics of Low-Temperature Plasma-Assisted Ignition of Ethanol-Gasoline Surrogate under Gasoline Engine like Conditions

ABSTRACT The plasma-assisted reaction kinetic mechanism for high-voltage nanosecond discharge at high pressure was developed for lean and stoichiometric ethanol-gasoline surrogate/O2/N2/AR mixture. The numerical results show that plasma-assisted ignition of ethanol-gasoline surrogate is mainly associated with the electron impact dissociation of O2, nC7H16, iC8H18 and C2H5OH molecules and excited O2* produced from electron impact during discharge phase. The generation of H and O atoms, radicals and O2* facilitates plasma-assisted ignition (PAI). The formation of C2H5OH+, C8H18 + and O− increases ignition delay time. PAI improves the ignition stability of lean mixture mainly by increasing the reaction rate in reaction iC8H18+ HO2⇋C8H17+ H2O2. The reaction CH3+ HO2⇋CH4+ O2 promotes auto-ignition. But it delays the plasma-assisted ignition of stoichiometric mixture while it facilitates plasma-assisted ignition in lean mixture. The ignition delay time in lean-burn conditions can be shortened only by a proper timing of low-temperature plasma discharge at low temperature.

An Experimental Study on Combustion and Cycle-by-Cycle Variations of an N-Butanol Engine with Hydrogen Direct Injection under Lean Burn Conditions.

This study experimentally investigated the effects of hydrogen direct injection on combustion and the cycle-by-cycle variations in a spark ignition n-butanol engine under lean burn conditions. For this purpose, a spark ignition engine installed with a hydrogen and n-butanol dual fuel injection system was specially developed. Experiments were conducted at four excess air ratios, four hydrogen fractions(φ(𝐻2)) and pure n-butanol. Engine speed and intake manifold absolute pressure (MAP) were kept at 1500 r/min and 43 kPa, respectively. The results indicate that the θ0–10 and θ10–90 decreased gradually with the increase in hydrogen fraction. Additionally, the indicated mean effective pressure (IMEP), the peak cylinder pressure (Pmax) and the maximum rate of pressure rise ((dP/dφ)max) increased gradually, while their cycle-by-cycle variations decreased with the increase in hydrogen fraction. In addition, the correlation between the (dP/dφ)max and its corresponding crank angle became weak with the increase in the excess air coefficient (λ), which tends to be strongly correlated with the increase in hydrogen fraction. The coefficient of variation of the Pmax and the IMEP increased with the increase in λ, while they decreased obviously after blending in the hydrogen under lean burn conditions. Furthermore, when λ was 1.0, a 5% hydrogen fraction improved the cycle-by-cycle variations most significantly. While a larger hydrogen fraction is needed to achieve the excellent combustion characteristics under lean burn conditions, hydrogen direct injection can promote combustion process and is beneficial for enhancing stable combustion and reducing the cycle-by-cycle variations.

Effect of ammonia addition on combustion and emission characteristics of hydrogen-fueled engine under lean-burn condition

Hydrogen (H 2 ) is a carbon-free fuel with many excellent combustion characteristics, but abnormal combustion is one of the main obstacles to the promotion and application of hydrogen-fueled engines. This experimental study aims to investigate the suppression of the heat release rate (HRR) of a hydrogen-fueled engine through the addition of ammonia (NH 3 ). The engine was run at 1300 rpm, with manifold absolute pressure (MAP) of 61 kPa and NH 3 addition ratio of 0% and 2.2%, under lean-burn conditions. The results showed that the addition of small amounts of ammonia reduced the combustion rate of the fuel mixture, prolonged the flame development period (CA0-10) and propagation durations (CA10-90) of the engine, and reduced the peak in-cylinder pressure and peak HRR under lean-burn conditions. The addition of ammonia increased the peak indicated mean effective pressure (IMEP) and the peak indicated thermal efficiency (ITE) of the engine. The addition of ammonia resulted in increased nitrogen oxides (NOx) emissions. • The effect of ignition timing of an H 2 /NH 3 dual-injection engine was studied. • Reduces the peak heat release rate after ammonia was added. • CA0-10 and CA10-90 were extended after ammonia was added. • The peak IMEP and ITE were increased after ammonia was added.

Reducing NOx Emission of Swirl-Stabilized Ammonia/Methane Tubular Flames through a Fuel-Oxidizer Mixing Strategy

Ammonia as a fuel can be a carbon-free and long-duration scalable hydrogen energy carrier. In the carbon-neutral power system, co-firing ammonia with natural gas is a promising technique for flexible operations of gas turbines and gas-fired boilers. However, the NOx propensity of ammonia/methane flames is a severe problem under global fuel-lean conditions. This work has investigated the NOx performance of various fuel-oxidizer mixing strategies on a tangential swirl burner. We propose a new ammonia co-combustion technology with a central ammonia jet surrounded by a group of separately tangential swirl methane jets. The NOx emissions can be reduced to about 1000 ppm under lean combustion conditions (global Φ = 0.5–0.9) when the ammonia blending ratio (ENH3, in terms of input energy) is 20% (corresponding to the ammonia molar fraction xNH3 as 0.41). Regarding the NOx emissions and ammonia slip at the tube exit, such a strategy outperforms other feed modes for a wide range of ammonia blending ratios (ENH3 up to 0.3 and xNH3 up to 0.52) and equivalence ratios (Φ ranging from 0.5 to 1.1). The variations of emitted NOx with the total flow rate and the axial position of ammonia injection were also studied. Combining measurements of gaseous temperature, composition, and NH2* chemiluminescence, we demonstrated the massive formation of NH2 radicals in the central high-temperature ammonia-rich zone. A model involving the chemical reaction network was developed and validated against the experiments. It provides further evidence for the role of NH2 radicals in reducing NOx emission.

Effect of peak firing pressure constraint on thermal efficiency of a Sabathe-Miller engine

How to Improve the thermal efficiency of internal combustion engine is an eternal topic since it is directly related to energy consumption and pollution emissions. Among lots of technologies applied on heavy duty diesel engine, Miller cycle which increases the effective expansion ratio in relation to the compression is proved to be a good choice to balance engine performance with fuel economy and CO2/NOx/smoke emissions. However, limitation of peak firing pressure (PFP) will restrict the intake pressure or compression ratio of miller engines which in turn influence the thermal efficiency, and their in-depth trade-off relationship is not clear yet. Using the engine cycle simulation, this paper explores the most reasonable cylinder pressure waveform limited by PFP and found there exists an optimized pressure ratio values which slightly affected by other operating conditions for Sabathe-Miller cycle engine. Thereafter, effects of PFP limit on the performance of a large single cylinder engine were investigated considering the effect of engine load, miller degree, equivalence ratio as well as engine speed. It is found that under full load condition, the maximum brake thermal efficiency occurs when pressure ratio (PR) is about 1.2, and PFP constraint plays a dominant role on brake efficiency and could contribute more than 4.0% efficiency by increasing PFP constraint from 250bar to 350bar. Compared with full load condition, the brake thermal efficiency increases 4.6% and 6.3% respectively under fuel-rich (extremely high CR) and lean-burn (low heat loss) half load conditions. Meanwhile, miller degree was optimized for Sabathe-Miller cycle, and it plays a key role on reducing combustion temperature instead of increasing thermal efficiency compared with effect of PFP constraint.

Numerical comparative analysis on performance and emission characteristics of methanol/hydrogen, ethanol/hydrogen and butanol/hydrogen blends fuels under lean burn conditions in SI engine

Hydrogen is currently recognized as a clean and renewable energy source, and it has broad prospects for being used in engines. Based on the author’s previous research experience on alcohol-gasoline, and previous researchers’ individual research basis on methanol-H2, ethanol-H2, or n-butanol-H2. An alcohol-H2 engine model is established through the GT-Power simulation platform, and the combustion and emission performance of methanol, ethanol and n-butanol under different hydrogen ratios are compared and analyzed. The results show that adding 10% hydrogen to methanol, ethanol or n-butanol can increase brake torque (BT) to 3.49%, 5.02% and 6.48% at 1500 r/min, respectively. At 2000 r/min, BT increased by 3.14%, 4.74%, and 6.62% respectively. At the same time, brake specific fuel consumption (BSFC) is reduced by 31.51%, 24.6% and 21.16% at 1500 r/min, respectively. At 2000 r/min, the BSFC is reduced by 31.37%, 24.4% and 21.23% respectively. HC, CO and CO2 emissions are reduced, but NOx emissions increase. At 10% hydrogen ratio, compared with ethanol-H2 and n-butanol-H2 blends, methanol-H2 blends can reduce CO by 48.28% and 65.91%, and CO2 by 14.9% and 24.61% at 2000r/min, respectively. When using a high proportion of hydrogen, it can better increase BT and reduce BSFC and carbon emissions.

Excellent activity caused by dielectric barrier discharge (DBD) plasma activation for selective catalytic reduction with propylene (C3H6-SCR): Insight into the low temperature catalytic behavior of Mn/ZSM-5 catalysts

For investigation of the low temperature catalytic behavior of C3H6-SCR, a series of Mn/ZSM-5 catalysts were synthesized by different activation and preparation methods for the first time. Under the simulated lean burn condition (5% O2) of actual diesel engines, more than 96% NO conversion was observed at 120–270 °C with the space velocity of 30,000 h−1 on the 7Mn/ZSM-5-CPM-DBD catalyst. The results showed that the excellent low temperature C3H6-SCR of 7Mn/ZSM-5-CPM-DBD catalyst was the shared effect between Brönsted acidity (hydroxyl) and oxygen vacancy on the surface, rather than the separate effect. Besides, the Mn/ZSM-5 catalysts with DBD plasma activation could generate higher dispersion of active species Mn, larger pore size, more abundant oxygen vacancies, and less destructive to zeolite than traditional calcination activation characterized by XRD, SEM, HR-TEM, EDS-mapping, ICP, BET, TG-DTA, XPS, and Py-FTIR. The study expects to shed more light on the nature of the surface active sites of Mn/ZSM-5 in low temperature C3H6-SCR, and the development of novel preparation method for the synthesis of highly active catalysts of low temperature C3H6-SCR.

Experimental study on combustion and emission of an SI engine with ethanol /gasoline combined injection and EGR

Ethanol is a widely used alternative fuel for sustainable development, showing potential for improving the combustion and emission characteristics. Both EGR and lean burn are important technical approaches for engines to reduce emissions In this paper, the performance EDI + GPI four-cylinder spark ignition engine at three access air ratios, five ethanol direct injection ratios and five exhaust recirculation ratios was studied at the speed of 1500rmp. The results show that, the cooperation of EDI and EGR can improve the engine performance. Under lean burn conditions, When 6%EGR+45%EDIr, CA 0-10 decreases 49. 8%. When 12%EGR+30%EDIr, BMEP increases 6. 59%, HC decreases 28.33%, total particle number decreases 93.87%. When 6%EGR+30%EDIr, Pmax increases 26.58%, crank angle corresponding to Pmax decreases 41.98%. And in this condition, CoVIMEP is only 1.46%, decreased 21.51% from the original engine. With the increase of λ, EGR limit of CO moves from 12% to 6%; the optimal ethanol direct injection ratio of CO moves from 30% to 15%. NOx decreases about 136.08 ppm with an average increase of 1% EGR. In summary, ethanol has a higher oxygen content and laminar flame speed is faster. EGR can not only reduce pumping losses and throttling losses, but also effectively accelerate the positive effects of ethanol on combustion and emissions. EGR + EDI + GPI can obviously increase the engine power performance, improve fuel economy and decline the emissions. When the engine speed = 1500 rpm, 12%EGR+30%EDIr is the optimal combination of SI engine at λ = 1.2.

Thermal efficiency improvement of lean burn high compression ratio engine coupled with water direct injection

The turbocharged downsizing gasoline direct injection (GDI) engines aiming for lower fuel consumption, lower emissions, and higher performance have been regarded as the future hybrid electrical vehicle (HEV) pathway. To improve the thermal efficiency of the HEV engine under lean burn operation, a water direct injection (WDI) system and a high-energy ignition (500 mJ) system were proposed in an Atkinson cycle GDI engine with a high compression ratio of 17. The effect of homogeneous lean burn, water injection ratio (WIR), and spark timing (ST) on engine knock, combustion process, and indicated thermal efficiency (ITE) improvement was studied. The result shows WDI at an earlier stage of the compression stroke (100° CA BTDC) could mitigate knock without significantly increasing combustion instability. When WIR increased to 50%, the engine knock decreased 82.7%, the indicated specific fuel consumption (ISFC) dropped 9.9% as the ST advanced from 1.6° to 9° CA BTDC. The maximum brake torque spark timing (MBT) could be further advanced by extending the lean burn limit (LBL). The wider LBL was achieved with a larger WIR. At λ = 1.1, CO emission reduced by 5 ∼ 7 times and reached 570 ppm, and unburned hydrocarbons were reduced by 9%∼13%. Less than 500 ppm of NOx was noted when λ ≥ 1.5 under each WIR case. The IMEP was extended from test basic 8.3 bar to 13 bar with an increase of 47.73%. The remarkably high ITE of 47.09% can be achieved with a controllable knock level at lean burn condition (λ = 1.9), with an increase of 7.84% compared with the stoichiometric test basic IMEP of 8.3 bar.

Radio-frequency (RF) plasma synthesis of H-ZSM-5 supported MnOx catalysts with high catalytic activity for deNOx-SCR by propylene

Traditionally, C3H6-SCR exhibited poor catalytic activity at low temperature (≤300 °C) due to the difficult activation of C3H6. For investigation of the low temperature catalytic behavior of C3H6-SCR, a series of MnOx/ZSM-5 catalysts prepared by coprecipitation method was activated by an efficient H2 RF plasma, and first used for C3H6-SCR. Under the simulated lean burn condition (5% O2) of actual diesel engines, more than 99% NO conversion was observed at 200°C–300 °C with the space velocity of 30000 h−1 on the MnOx/ZSM-5-H2RF-100W catalyst. Characterization results demonstrated that H2 RF plasma activation could facilitate the growth of stronger active Mn2O3 species, and generated more lattice oxygen (Oβ) with a high electron cloud density. Besides, the stable Brönsted acidity from uncoordinated framework Mn (Mn–O–Si), higher surface Mn concentration, good dispersion, and larger pore size caused by H2 RF plasma could be also contribute to excellent low temperature C3H6-SCR catalytic activity. We expect this study to shed more light on the nature of the surface active sites of MnOx/ZSM-5-H2RF-100W in low temperature C3H6-SCR, and the development of novel preparation method for the synthesis highly-active catalysts of low temperature C3H6-SCR.