Peak Combustion Pressure Research Articles

Experimental Study of Turbulent Premixed Flames of Gas-to-Liquids (GTL) Fuel in a Fan-Stirred Combustion Bomb

This study experimentally investigates the turbulent flame speeds (St) of Gas-to-Liquids (GTL) fuel and a 50/50 blend with diesel across turbulence intensities (u') ranging from 0.5 to 3.0 m/s and equivalence ratios (Φ) from 0.7 to 1.3. Experiments were conducted using a cylindrical fan-stirred combustion bomb at an initial temperature (Ti) of 463 K and atmospheric pressure under near homogeneous and isotropic turbulence (HIT) conditions. A pressure transducer measured the St of the propagating GTL flame. High-speed imaging reveals that changes in flame brightness are associated with variations in flame temperature and soot incandescence. Compared to diesel, stoichiometric GTL and the 50/50 diesel-GTL blend showed peak combustion pressure reductions of 8.9% and 4.9%, respectively. Rich diesel fuel and lean GTL exhibited higher pressure rise rates, flame propagation, and St due to their Lewis numbers (Le) being less than one, enhancing flame-turbulence interaction. At u` of 0.5, 1.5, and 3.0 m/s, St for GTL increased by approximately 3.6%, 5.3%, and 2.8%, respectively, when compared to diesel, with these increases observed at Φ < 1.1. Transition from wrinkled to corrugated flamelets with increasing u` supports models predicting flame stability and potential industrial combustion efficiency improvements. Comparisons with numerical St results using the Zimont Turbulent Flame Speed Closure (Zimont TFC) model showed good agreement at lower (u' = 0.5 m/s) and mid-range (u' = 2.0 m/s) turbulence intensities but discrepancies at higher intensities (u' = 3.0 m/s), highlighting the need to refine numerical models for more accurate predictions across all turbulence levels.

Experimental study on the effects of n-butanol and n-propanol on the spray and combustion characteristics of diesel/biodiesel blends in a constant volume combustion chamber

The depletion of fossil fuel resources and the escalating environmental impact of greenhouse gas emissions have intensified the global exploration of renewable and sustainable energy sources. Biodiesel produced from vegetable oils and animal fats has become a promising alternative to conventional diesel fuel due to its renewability and lower carbon emission. This study investigates the differences in spray, combustion and flame characteristics between soybean-based biodiesel blended with propanol and butanol at various ratios. The results indicate that the liquid spray penetration length of biodiesel mixed with propanol and butanol exceeds that of soybean-based biodiesel. And the increase of spray penetration is accompanied by a longer flame lift-off length, which indicates the improvement of spray characteristics. Regarding combustion, alcohol-fuel blends exhibit a reduction in peak combustion pressure but an increase in peak apparent heat release rate. Additionally, these fuels show a shorter ignition delay and combustion duration. The peak natural flame luminosity is lower for alcohol fuels, suggesting their potential to reduce carbon soot production and support low-carbon combustion. These experimental results contribute to advancing research on cleaner, more efficient and renewable fuels, thereby reducing reliance on conventional fossil fuels.

Exploring direct injection strategies for improved combustion efficiency and emissions reduction in dual-fueled RCCI/compressed natural gas engine: A experimental survey

ABSTRACT The dwindling reserves of conventional fuels have spurred research into alternative options for diesel engine, particularly given diesel’s widespread use in global public transportation. Environmental concerns, notably regarding oxide of nitrogen (NOx), and smoke necessitate a shift toward alternative fuels. Diesel’s partial replacement with compressed natural gas in CI engines has shown promise in mitigating smoke and NOx emissions. The Present research utilized an RCCI engine, and employed combinations of Diesel+CNG dual-fuel to analyze how direct injection techniques affect performance, emission, and combustion features. Under full load conditions sans exhaust gas recirculation (EGR) 6 ms and 8 ms CNG yielded superior brake thermal efficiency (BTE) of 30.5% and 29.5% surpassing diesel’s 26%, although excessive CNG induction disrupted combustion, reducing efficiency, and introducing EGR, particularly at 10% enhanced BTE, with 6 ms CNG achieving a peak of 32.5%, slightly lower at 15% EGR with 30.9%. Diesel engine showcased diminishing brake-specific fuel consumption values with CNG supplementation, further mitigated by increased CNG concentrations and EGR rates. Peak combustion pressure decreased in the RCCI engine, with promising results seen at 6 ms CNG, comparable to pure diesel. EGR introduced pressure fluctuations, signifying a dilution effect on combustion, while the net heat release rate displayed increasing trends for CNG, stabilizing with EGR. NOx emissions, peaking in diesel engine, showed reductions with 6 ms CNG, further diminished with EGR implementation.

Machine learning based prognostics and statistical optimization of the performance of biogas-biodiesel blends powered engine

In this study, waste biomass-derived biogas was employed as the main fuel while the biodiesel-diesel blend was used as pilot fuel. This paper describes the development of a Decision Tree and Response Surface methodology-based statistical framework for prediction modeling and optimization. The compression ratio, fuel injection time, fuel injection pressure, and biogas flow rate were employed as controllable inputs, and brake thermal efficiency, peak combustion pressure, and exhaust emission were selected as responses. The experimental data for model development was gathered for the development of prediction models and optimization. The decision tree-based models were robust with almost negligible mean squared errors and R2 values of more than 0.9487 for all models. Response surface methodology-based optimized engine parameters were validated with the following results compression ratio was 17.9, fuel injection pressure was 225 bar, fuel injection timing was 26.3-degree crank angle after top dead center, and the biogas flow rate was 0.85 kg/h. Validation results were within 5 % of the model-optimized results. The prognostic models for all control factors were developed with decision tree-based machine learning with high predictive efficiency and low errors.

Electrical ignition of ADN-based green liquid propellant in constant volume combustion chamber and continuous flow

Ammonium dinitramide (ADN) propellant for green space propulsion is perceived as a focal point in space propulsion research. The development of electrical ignition methods to realize the ignition for ADN-based liquid propellant can overcome the technical bottleneck of the catalytic ignition methods currently applied to ADN-based space thrusters. This work presents an experimental investigation of the electrical ignition and combustion characteristics of an ADN-based liquid propellant in a constant volume combustion chamber, considering ignition voltages and initial pressures. It is observed that increasing the ignition voltage and initial pressure reduces the flame retardation period, combustion duration, droplet lifetime, ignition energy, and total energy. Also, the combustion peak pressure decreases with an increase in the ignition voltage but increases with higher initial pressures. The energy consumption is mainly concentrated in the ignition stage, with the ignition energy accounting for approximately 76% to 96% of the total energy. The measurement of the concentrations of the keycombustion products are reported, highlighting that the mole fraction of CO decreases with an increase in ignition voltage and pressure. The ignition and combustion of the ADN-based liquid propellant in continuous flow were achieved for the first time through a combination of resistive ignition and high-temperature arc-assisted combustion. During the testing of the propellant ignition in continuous flow, there is a need for a continuous supply of electrical energy, and the combustion cannot be self-sustaining.

Tuning combustion and energy in hydroxylammonium nitrate (HAN)-based electrically controlled solid propellant

Solid propellants have been widely applied due to its high energy, rapid reaction, easy storage and convenient equipment. However, the further development of solid propellants has been hindered by the challenges associated with controlling their combustion process. In this research, we presented an electrically controlled solid propellant (ECSP), and its burning rate could be continuously adjusted with voltage. We investigated thermal decomposition behavior and gaseous products of ECSP using thermogravimetry–differential scanning calorimetry-mass spectrometry (TG-DSC-MS). The solid products were analyzed through energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Based on the thermal decomposition behavior, gaseous products, and solid products, it was found that the thermal decomposition process could be divided into two stages: decomposition of ammonium nitrate (AN) and interactions between hydroxylamine nitrate (HAN) and other substances. The electrochemical impedance spectroscopy (EIS) experiments revealed that the electrical conductivity of ECSP increased with the pressure. Significantly, the peak combustion pressure of propellant increased by the rise of voltage from 3.17 MPa (150 V) to 5 MPa (250 V) in closed bomb. In addition, electricity reinforced the burning rate and powder force of propellant. Additionally, the electricity simultaneously affects electric and thermal decomposition processes. Electricity is used to control the burning rate and the total energy produced by propellant combustion. The characteristics of controllable energy has the potential to achieve controllable range of weapons, providing a new direction for development of smart weapons.

Studies on Biodiesel and Hydrogen Powered Dual Fuel Common Rail Direct Injection Engine

Objectives: To evaluate the effect of hydrogen and used temple oil biodiesel (BTO) combination on the performance of Common Rail Direct Injection (CRDi) engine. To report the maximum possible flow rate (HFR) for knock free operation of the engine at a speed of 1500 RPM. Methods: Transesterification process was used to get BTO. was inducted through intake manifold. BTO was injected into engine cylinder using electronically controlled technique. Findings: The study revealed that the peak HFR was for BTO and 0.24 for diesel at an Injection Pressure (IP) of 800 bar and Injection Timing (IT) of before top dead center (bTDC). The Dual Fuel (DF) CRDi engine with Toriodal Reentrant Combustion Chamber (TRCC) shape yielded 6% to lower Brake Thermal Efficiency (BTE) with reduced exhaust gas emissions except 19 to higher oxides of nitrogen (NOx) at and 100% loads. Both Peak Combustion Pressure (PP) and Heat Release Rate (HRR) were 5 to 9% higher than BTO run diesel engine operation. Combustion Duration (CD) and Ignition Delay (ID) were 6 to 15% lower in DF CRDi operation with . Novelty: Diesel engine comes with hemispherical combustion chamber (HCC). Toriodal Reentrant Shaped Combustion Chamber (TRCC) was adopted in place of HCC which results better mixing of air and fuel. and BTO combination was used to power CRDi engine. Electronically controlled fuel injection system developed and fitted to conventional diesel engine. Keywords: Used temple oil biodiesel (BTO); Common rail direct injection (CRDi) engine; Toriodal reentrant combustion chamber (TRCC); Hydrogen flow rate (HFR); Hydrogen-biodiesel energy ratio (H2BER)

Comparative study on combustion and emission characteristics of gas-to-liquid with diesel on a burner and a naturally aspirated compression ignition engine

ABSTRACT Due to the consumption of fossil fuels and the generation of harmful emissions by diesel engines, researchers are seeking alternative fuels for diesel, for example, gas-to-liquid (GTL). However, most studies on combustion and emission of GTL focused on the fuel burned on turbocharged heavy-duty diesel engines. The purpose of this study is to reveal the combustion, fuel economy, and emission characteristics of GTL by a burner and a naturally aspirated (NA), fuel direct injection compression ignition light-duty engine. Comparative experiments of the GTL to fossil diesel were carried out, respectively. The burner has good consistency with the diesel engine in revealing emission trends. The results of the burner test showed that GTL produced less flame smoke and its flame height was 5.3% lower than diesel. The results of the engine bench test revealed that the combustion and emissions of the GTL with diesel were significantly different. Compared to diesel, the ignition of GTL began earlier from 1.5°CA to2.5°CA though the combustion was slower in contrast to diesel. The diffusion combustion maximum pressure was considerably 4.8% higher and occurred earlier with 2.2°CA-3°CA, and the premixed combustion peak pressure of GTL was slightly beyond the diesel. The peak of premixed combustion heat release rate (HRR) for GTL was less than that of diesel by 18.9%. While the peak HRR of diffusion combustion was greater by 38.4%. The maximum PRR value of GTL was lower than that of diesel leading to soft combustion. In all test conditions, the brake specific fuel consumption of GTL averagely reduced by 4.7% against diesel, and the brake thermal efficiency was on average 4.3% higher. GTL engine can reduce regular emissions of carbon monoxide, hydrocarbons, nitrogen oxide (NOx), smoke, and particle number (PN) simultaneously. It is worth noting that GTL improved the trade-off issue of NOx and smoke, simultaneously reducing 18.8% NOx and 24.1% smoke on average. The experimental results reveal the GTL is an appropriate alternative fuel for light-duty diesel engine without modification of mechanical fuel system.

Performance and energy balance analysis of the downsized SI engine with using a novel OPCVCR and synchronized twin spark plugs configurations

Recently, the exhaust emissions become one of the main issues in the downsizing spark ignition (SI) engine. It is necessary to develop clean combustion and high efficiency SI engines for further increasing the performance and brake thermal efficiency. In this study, a novel opposite piston type continuous variable compression ratio (OPCVCR) mechanism combined with synchronous twin spark plugs configurations was proposed and applied in the turbocharged downsizing SI engine. The purpose of this study was to propose a novel type of OPCVCR engine and analyze its combustion, performance and energy balance characteristics. The results showed that the peak combustion temperature (PCT) and peak combustion pressure (PCP) of the OPCVCR engine with twin spark plugs were increased when the compression ratio (CR) increased. The knocking combustion intensity of the downsized SI engine was increased when the CR increased, while the knocking combustion intensity can be alleviated effectively by introducing the external EGR. In addition, the energy utilization efficiency was increased with increasing the CR of the OPCVCR engine with twin spark plugs. Besides, the indicated specific fuel consumption (ISFC) of the base downsized SI engine could be decreased by 23.59% and the indicated thermal efficiency (ITE) of the base downsized SI engine could be increased 21.62% by adopting CR 16 and introducing 10% external exhaust gas recirculation (EGR), respectively.

Deprotonation-assisted electrochemical synthesis of copper nitrotriazole with excellent ignition performance

Electrochemical synthesis serves as a green and efficient method with great application potential. However, it has not been extensively applied in the synthesis of energetic materials. Nitrogen-rich heterocyclic compounds, as a new generation of energetic materials, enjoy advantages such as eco-friendliness, high energy output, and excellent safety performance. This study reports the electrochemical cathodic synthesis of copper nitrotriazole [Cu(NTz)2] using copper chloride and 3-nitro-1,2,4-triazole as a reaction substrate and triethylamine as a deprotonation agent. The obtained Cu(NTz)2 comprises uniform spherical particles of nano lamellae. As the dosage of triethylamine increased from 50 μL to 150 μL, Cu(NTz)2 gradually grew into compact solid spherical particles, significantly increasing the energy output. Notably, the heat release increased from 711 J g−1 to 1301 J g−1, accompanied by a significant positive elevation of ignition performance and peak combustion pressure in the process of confined combustion. This greatly boosted the energetic performance of Cu(NTz)2. Moreover, Cu(NTz)2 demonstrates insensitivity to electrostatic discharge (E50＞225 mJ) and friction (FS＞360 N), suggesting excellent safety performance. Owing to its outstanding energetic and safety performance, Cu(NTz)2 boasts great potential for application as pyrotechnic compositions, including military gas-producing and incendiary agents. Moreover, it has been corroborated that Cu(NTz)2 can be applied as a micro ignitor.

Effect of ammonia addition on combustion characteristics of hydrogen/air using passive turbulent jet ignition

Hydrogen (H2) and ammonia (NH3) are ideal carbon-free fuels, and the application of NH3/H2 in internal combustion engines offers the potential to reduce carbon emissions. And turbulent jet ignition (TJI) is an advanced ignition strategy that can effectively enhance the combustion. This work aims to experimentally investigate the effect of NH3 addition on the combustion characteristics of H2/air mixtures under passive TJI conditions. Combustion images and instantaneous pressure were collected for processing and analysis. The effect of NH3 substitution and equivalence ratio were investigated. The results indicate that the peak combustion pressure decreases with the addition of NH3, accompanied by longer combustion duration and ignition delay, as well as lower jet velocity and flame area growth rate. The hot jet will be quenched by the strong heat transfer, causing the change in the ignition mechanism as the NH3 substitution ratio increases. In addition, compared to lean conditions, the combustion appears to be less sensitive to the equivalence ratio on the rich side and always shows high jet velocity and flame propagation speed. However, a relatively small amount of NH3 addition changes the ignition mechanism on the rich combustion side compared with lean conditions, resulting in a longer ignition delay.

Effect of injection strategy on an air-assisted direct injection aviation kerosene two-stroke engine

In small aviation piston engines, the atomization and combustion of aviation kerosene have attracted much attention. Due to the low volatility and high viscosity of aviation kerosene, high-pressure injection or air-assisted injection is used to improve the fuel atomization quality. Considering the weight, cost and power consumption, air-assisted injection is more appropriate for compact, small aviation piston engines. In the paper, computational fluid dynamics (CFD) software was used to simulate the air-assisted spray and spark ignition combustion of aviation kerosene in a heavy-fuel direct injection spark ignition (DISI) two-stroke engine based on air-assisted direct injection (AADI) technology. The effects of injection pressure, single and double injection on formation and combustion characteristics of the aviation kerosene/air mixture were analyzed. The results show that increasing the air-assisted injection pressure can promote air flow in the cylinder and accelerate fuel evaporation, but also increase the film mass on the combustion chamber wall. When single injection is employed, high combustion pressure and temperature are generated, and the tendency to knocking combustion is greater. The use of double injection can effectively achieve fuel stratification and reduce knock tendency. With the delay of the second mixture injection timing, the peak combustion pressure is reduced, the heat release rate is slowed down, and the knock tendency is reduced correspondingly.

Effects of magnesium hydride on the thermal decomposition and combustion properties of DAP-4

Ammonium perchlorate-based molecular perovskites (DAP-4) have garnered immense interest due to their exceptional burst performance and good thermal stability. Similarly, metallic hydrides are widely acknowledged as an exceedingly promising material class for implementation in energetic systems, given their exceptional hydrogen storage density. Therefore, it is crucial to investigate the impact of hydrogen storage material MgH2 on the thermal decomposition and combustion characteristics of molecular perovskite materials ((H2dabco)[NH4(ClO4)3],DAP-4). In this study, DAP-4/MgH2 composites were synthesized and characterized for their morphology, structure, elemental distribution, thermal decomposition properties, and combustion properties. The findings indicated that the inclusion of MgH2 reduce the thermal decomposition temperature of DAP-4. Moreover, when MgH2 was added at a mass ratio of 5 wt%, the apparent activation energy (Ea) decreased to 212.0 kJ/mol, while the peak combustion pressure and boosting rate increased with more intense flames. A plausible thermal decomposition and combustion mechanism of DAP-4/MgH2 composites was postulated. This study enhances our understanding of the thermal decomposition and combustion properties of DAP-4 and magnesium hydride in energy-containing systems.

Impact of crude palm oil on engine performance, emission product, deposit formation, and lubricating oil degradation of low-speed diesel engine: An experimental study

The higher emissions are one of the main issues associated with the use of diesel power plants. Therefore, various previous studies have been conducted on the substitution of diesel with renewable base liquid fuels for internal combustion engines, such as Crude Palm Oil (CPO). In this study, a comprehensive evaluation was carried out on the impact of using CPO on a low-speed diesel engine with a large capacity. The objective of this study is to determine the viability of modifying the existing diesel engine to operate on CPO fuel, with the aim of minimizing the requirement for additional capital expenditures. Furthermore, a diesel power plant engine with a rated capacity of 2554 kW and a rated speed of 600 RPM using a modified injector was employed. The testing phase was divided into two stages namely, a performance test for 7 h and a running test for 375 h. During the running test, the level of emission was also tested with different load variations using a portable flue gas analyzer. Following this, the lubrication oil sample was collected both before and after the engine running test. The deposits sample obtained from the engine was analyzed using SEM-EDX. Prior to being introduced into the engine, the fuel pre-treatment plant ensured that the kinematic viscosity and temperature of the CPO were properly maintained. The results show that operating the low-speed diesel engine with the continuous use of 100% CPO is not recommended due to the reducing of the engine gross power, the peak combustion pressure, the engine's IHP (indicated horse power) and the exhaust temperature of each cylinder. Furthermore, deposits were found on the cylinder head, piston, valve, and nozzle. Besides, the lubricating oil quality also degraded. Therefore, necessary to conduct a comprehensive study on the technical and financial aspects of using other biofuels that have a minimal risk impact on engine reliability and performance as an alternative to diesel or biodiesel fuel in low-speed diesel power plants.

Rocket-augmented flame stabilization and combustion in a cavity-based scramjet

The scramjet engine has become an important propulsion system in hypersonic vehicles for its high specific impulse, but it also has obvious shortcomings, such as narrow reliable operating and thrust adjustment range, and consequently, insufficient maneuverability. To solve these problems, a rocket is introduced into the scramjet to improve the thrust performance while stabilizing flame and enhancing combustion, referring to the operating principle of the RBCC engine. The function mechanism of the high mass flow rate rocket jet on the flame stability and combustion characteristics in a cavity-based scramjet combustor is investigated through the ground direct-connect test. The experimental results show that: 1) Effective secondary fuel combustion enhancement and thrust enhancement can be obtained through the rocket augmentation. The embedded rocket leads to a 69% increase in the peak combustion pressure. 2) In the rocket-augmented combustion mode, the core combustion zone concentrates in the central region of the flow passage and simultaneously expands upstream, resulting from the increased mixing efficiency of kerosene/air and a more stable flame, which effectively augments the combustion and the engine thrust. 3) As the kerosene injection positions move upstream to the exit of the rocket nozzle, the secondary combustion efficiency can be further improved by inhibiting the negative effects of oxygen consumption by the fuel-rich rocket jet. The length of the high combustion pressure region is increased by 150%, and the scramjet performance has been enhanced significantly. 4) During the process of the kerosene injection position transition, the flame in the combustor keeps sustained under the function of the embedded rocket jet, and the rocket-augmented combustion exhibits favorable robustness.

Combustion characteristics and concentration measurement of ADN-based liquid propellant with electrical ignition method in a combustion chamber

An experimental study was performed to investigate combustion characteristics of ammonium dinitramide (ADN) based liquid propellant with electrical ignition method in a combustion chamber. The experiment was conducted in different gas atmospheres such as argon, air and nitrous oxide under an on-load voltage range of 60–100 V. The influence of the gas atmosphere, on-load voltage on the ignition delay time, peak combustion pressure, ignition energy, total energy and key reaction products mole fractions were studied. The ignition delay time of propellant decreases gradually with the increase of ignition voltage, while the ambient gas has little effect on the ignition delay time because the flame appears inside the propellant earliest. The peak combustion pressure of propellant is highest when the ambient gas is nitrous oxide, whereas lowest in argon atmosphere. The ignition energy and total energy are insensitive to gas atmosphere and decrease gradually with the increasing on-load voltage. The concentration of N2O increases with the increase of on-load voltage. The mole fraction of CO decreases with the increase of on-load voltage in general, especially obviously at relatively high on-load voltage of 100 V.

Using oxy-hydrogen gas to enhance efficacy and reduce emissions of diesel engine

The ever-increasing need for energy, along with diminishing petroleum supplies, has prompted the quest for renewable and sustainable alternative fuels. The goal of this research is to investigate theoretically the impact of using HHO gas on single-cylinder diesel engine characteristics using the simulation software diesel-RK model. Diesel fuel blended with 10% HHO gas is used and tested under different engine speeds. When 10% HHO gas was put into the engine, the thermal efficiency climbed to 31.5 percent and consequently, fuel consumption is reduced by up to 20 percent. The maximum reduction in BSN is 25% which is witnessed at 3500 rpm. The findings are corroborated by the findings of other studies. Among the most important outcomes that were obtained the peak combustion pressure was raised by 10% as compared to diesel fuel without HHO and the brake power enhances from (9% to 16%) when the engine speed is increased from (1500 to 3500) rpm.

Study of PCCI engine operating on pine oil diesel blend (P50) with benzyl alcohol and diethyl ether

This article examines the effect of premixing of benzyl alcohol and Diethyl Ether (DEE) in a CI engine fuelled with pine oil diesel fuel blend. The fuel sample is prepared by blending 50% of pine oil with 50% of diesel fuel (P50) on volume basics. The benzyl alcohol and diethyl ether were injected in the premixing ratio of 10% and 20% on the CI engine fuelled with P50. The experimental analysis was conducted in a 4-stroke single cylinder CI engine with added provision to operate on PCCI mode. The engine was operated with constant speed and tested at different torque condition ranging from 0 to 100 % in the interval of 25%. The experiment results shows that premixing of benzyl alcohol and diethyl ether enhanced the brake thermal efficiency by 4.5 % and 8.75 % than P50 respectively and brake specific energy consumptions was low when compared to neat P50 operation. Premixing of diethyl ether and benzyl alcohol increased the emission of CO and HC whereas reduced smoke and NOx emission. There was increase in peak combustion pressure and heat release rate with the premixing of benzyl alcohol however, premixing of diethyl ether resulted in reverse trend.

Water Vapor Blending Ratio Effects on Combustion Thermal Performance and Emission of Hydrogen Homogeneous Charge Compression Ignition

A numerical model of the micro-free-piston engine was developed and its correctness was verified by the comparison between the simulation and referential experiment results under the same work conditions. Based on this numerical model, the effects of the water vapor blending ratio (α) on combustion thermal performance and emission characteristics of hydrogen (H2) homogeneous charge compressing ignition (HCCI) were investigated numerically. The water vapor impact on combustion temperature was analyzed as well. The simulation results reveal that when the initial equivalent ratio is 0.5, blending H2 with water vapor can delay the ignition time and prolong the whole process. At the same time, the addition of water vapor to H2 decreases the peak combustion temperature and pressure, which will alleviate the detonation phenomenon of the combustion chamber. Moreover, the power output capacity and NOx emissions decrease with the increase in α. When α increases to 0.8, the mixture gas cannot be compressed to ignite. Finally, the dilution effect, thermal effect, and chemical effect of water vapor all have the potential to lower the combustion temperature and the dilution effect plays the leading role.

Laminar combustion characteristics of methane/methanol/air mixtures: Experimental and kinetic investigations

Methanol has been studied to solve the problems of insufficient combustion and unstable operation of natural gas engines. To explore the influence of methanol addition on natural gas/air mixture, the laminar combustion characteristics of stoichiometric methane/methanol/air mixture with methanol volume fractions of 0–100% are measured in a constant volume combustion chamber under the initial pressures of 1–4 bar and initial temperatures of 353–393 K. The experimental results show that the laminar combustion characteristics are linearly enhanced by methanol addition. When the methanol volume fraction varies from 0% to 100% at 393 K and 4 bar, the change rates are 11.7%, 120.4%, - 28.1% and 61.7% for combustion peak pressure, maximum pressure rise rate, combustion duration and laminar burning velocity (LBV) respectively. At high pressure, the influence of methanol addition is enhanced. Chemical kinetics analysis shows that CH2OH, the intermediate product of methanol oxidation, generates HO2 through R134: CH2OH + O2<=>CH2O + HO2, which contributes from 14% to 56% to the generation of HO2, so that HO2 replaces part of the O2 to participate the reaction with H, resulting in the transformation of part of R1: H + O2<=>OH + O to R10: HO2+H<=>2OH, thereby generating more OH and promoting the reaction.