Lean Combustion Mode Research Articles

Effects of industrial hydrogen-rich gases on the performance of the spark ignition engine under various combustion modes

Hydrogen is emerging as a promising alternative to traditional fossil fuels for the transportation. Additionally, the hydrogen-rich gases (HRG) can produce on a large scale during the process of chemical production. In this study, the influences of HRG on the performance behaviors of the spark ignition (SI) engine are comprehensively analyzed under various combustion modes and operating conditions. The experimental results indicate that with increasing the lambda, the torque of the test engine can maintain the target value under equivalent ratio and lean combustion modes, while it sharply decreases under ultra-lean combustion. When the value of the lambda is 1.5, the brake thermal efficiency (BTE) and brake specific hydrogen consumption (BSHC) of the HRG SI engine respectively reach up to 33.6% and 89.1 g/kW.h, yielding superior fuel economy. The NOx emissions of the HRG SI engine firstly increase and then decrease with increasing lambda, reaching the peak value at the lambda of 1.1. In addition, the NOx, CO, and HC emissions of the HRG SI engine greatly reduce when the lambda is approximately 1.5. Consequently, using HRG partially substitute the traditional fossil gasoline in the SI engine can benefit to achieve energy conservation and emissions reduction in transportation section.

Tomographic Reconstruction Of Combustion Flow Fields From Density Measurements Based On Physics-Informed Neural Networks

Achieving stable, low-emission combustion with green hydrogen is crucial for climate-neutral ground-based power generation in turbomachinery. Lean combustion modes with green hydrogen reduce fuel consumption but increase unsteadiness. Thus, multimodal detection techniques for parameters like density and flow velocity are essential to understand the interconnected behavior of combustion, advection velocity and noise production. We previously introduced a high-speed camera-based laser interferometric vibrometer system to detect thermoacoustic oscillations and record advection velocities, using interferometric detection of density fluctuations and correlation-based velocity estimation. However, this method only estimates integral velocity fields, necessitating the solution of the inverse problem. This is relying on iterative optimization, which is computationally expensive and struggles with high dimensional, noisy or limited data. Physics-Informed Neural Networks offer an innovative and efficient approach to these problems, combining neural network flexibility with physical law constraints to unravel intricate cause-effect relationships. Here an approach for reconstructing local velocity fields from a single projection velocity calculated from integral density data is presented. Using a U-net and model assumptions for coupling local and integral velocity fields, the training minimizes errors between measured integral input fields and the predicted local field integrals. The comparison of measured local velocity and the network prediction achieved a relative mean squared error of 3 %.

Impact of hydrogen direct injection on engine combustion and emissions in a GDI engine

The combustion and emission characteristics of a hydrogen engine were investigated through experimental analysis using a GDI engine. To enable hydrogen in-cylinder direct injection, a specialized hydrogen gas injector was employed. A comparative analysis of the combustion performance between gasoline and hydrogen fuels in a spark-ignited engine was conducted. Additionally, the study experimentally explored the thermal efficiency and emission reduction potential of hydrogen engines in lean combustion modes. The results indicated a significant improvement in the combustion rate when hydrogen fuel was utilized in the spark-ignited engine. However, the effective thermal efficiency was found to be lower than that of gasoline fuel due to the delayed MBF50 under stoichiometric conditions. Furthermore, when compared to gasoline fuel, the reduction of CO and THC emissions was accompanied by an increase in NOx emissions. Nevertheless, optimizing the air dilution ratio in hydrogen engines led to an improvement in the effective thermal efficiency. Specifically, under medium load conditions, a Lambda value of 2.7 resulted in an effective thermal efficiency of 43.5%. Additionally, under ultra-lean conditions (Lambda > 2.3), NOx emissions could be reduced to below 50 ppm, reaching as low as 44 ppm. This study highlights the potential of improving combustion efficiency and reducing emissions by utilizing hydrogen fuel, particularly in lean combustion modes. It contributes to the continuous development of hydrogen engine technology and promotes the implementation of cleaner and more efficient energy solutions.

Characterization of in-cylinder spatiotemporal flame and solid particle emissions for ethanol-gasoline blended in gasoline direct injection engines

Stricter regulations for internal combustion engines have necessitated the inclusion of eco-friendly fuels with conventional ones to reduce gas and solid emissions. Gasoline direct injection (GDI) engines, however, have been found to produce more particle number and mass emissions than port fuel injection engines. To address this, bioethanol fuel has been selected as an additive eco-friendly fuel for gasoline, with the aim of reducing particle emissions. In this study, we quantitatively characterize in-cylinder spatiotemporal flame to feature combustion performance and particle emissions for ethanol fuel in the GDI combustion chamber. We examined three engine combustion modes differed in equivalence ratio and injection strategy to produce various combustion results to quantify combustion performance and particle emission characteristics. Using an eight-channel non-intrusive flame luminosity sensor in one cylinder, we measured the flame front and its propagation direction. At the tailpipe, we measured particulate emissions using an engine exhaust particle sizer and a micro soot sensor coupled with a catalytic stripper that removed semi-volatile compounds. Our study found that increasing ethanol fuel content for different combustion modes resulted in distinct combustion and flame development. The particle size distribution also showed different patterns at each combustion mode, depending on the ethanol content. Lean combustion modes yielded high diffusion flame intensity compared to stoichiometric combustion mode, which resulted in a larger amount of particle formation. The physical properties of ethanol fuel were found to predominantly determine the fuel-air mixture quality, combustion process, and flame development at each combustion mode. An increase in ethanol fuel content at lean-homogeneous mode resulted in higher diffusion flame intensity and larger particle emissions. Our comparative study of flame and solid particles for ethanol fuel content improves the understanding of in-cylinder combustion processes and their correlations.

Experimental Investigation about the Effect of Double-Spark Plug Ignition on Combustion Characteristics for Motorcycle Gasoline Engines with a Mild Lean Mixture.

To investigate the effect of double-spark plug ignition (DSI) on the mild lean combustion characteristics of motorcycle gasoline engines, three combustion modes were set up on a gasoline engine for testing, namely, the single-spark plug ignition (SSI) stoichiometric combustion mode (λ = 1, λ represents the excess air coefficient), the DSI stoichiometric combustion mode (λ = 1), and the DSI mild lean combustion mode (λ = 1.1). The results show that the double-spark plug ignition as that in the DSI mild lean combustion mode and DSI stoichiometric combustion mode is more prominent in accelerating the combustion process, reducing the cyclic variation, and improving the lean burn stability. It is verified that the overall effect of double-spark plug ignition on accelerating mildly homogeneous lean combustion is mainly reflected during the early period of rapid burning, which improves the stability of mildly homogeneous lean combustion and extends the lean burn limit. Further, the bench test shows that at a moderate load, the DSI mild lean combustion mode can result in lower brake-specific fuel consumption (BSFC) compared to that of the DSI stoichiometric combustion mode. When using the DSI mild lean combustion mode, the fuel economy can be improved by about 3–6% compared to that when using the SSI stoichiometric combustion mode. And the emission reduction can also be clearly observed when using a three-way catalyst containing rare-earth materials. However, at a low load, limited by combustion stability, for the DSI mild lean combustion mode, λ should not exceed 1.05.

Impact of coolant temperature on the combustion characteristics and emissions of a stratified-charge direct-injection spark-ignition engine fueled with E30

The direct injection spark ignition (DISI) engine has received considerable attention due to its potential to increase the power density of traditional spark ignition engines while significantly improving fuel economy through lean, unthrottled combustion. However, the market introduction of DISI engines operated in a lean combustion mode is inhibited by their unsatisfactory emissions, especially during cold start conditions that make proper mixture formation more challenging. Ethanol-blended gasoline, now a widely used fuel, makes the cold start of a DISI engine more difficult, leading to higher HC and soot emissions because of the high latent heat of vaporization of ethanol relative to gasoline. This work investigated the impact of coolant temperature on the characteristics of combustion and emissions in a stratified-charge DISI engine fueled with an E30 fuel (i.e. 30% ethanol in gasoline), while the coolant temperature was alternated between four levels (45, 60, 75, and 90 °C) to simulate different conditions throughout the warm-up process. The experiments showed that the coolant temperature affected the post-spark inflammation time, as well as the speed, intensity, and stability of the combustion process in the engine. When the coolant temperature rose, the engine produced more NOX and less CO, PM and HC. In addition, high-speed direct photography was used to obtain crank-angle resolved images of fuel sprays and flames in the cylinder. As the coolant temperature rose, the liquid spray lengths became shorter, reducing the possibility of wall wetting, and reduced irradiance from soot particles also indicated less non-premixed combustion. The in-cylinder imaging results are consistent with the observed combustion and emission characteristics and shed light on the underlying processes. Some potential solutions to the emissions challenges faced here could be either raising in-cylinder temperatures by using trapped residuals or modifying the injection schedule, for example by increasing the number of injections or to inject later in the cycle into a higher-density environment.

Comparative assessment of stoichiometric and lean combustion modes in boosted spark-ignition engine fueled with syngas

Synthesis gas (syngas) is considered an intermediate step between conventional carbon-based fuels and future hydrogen-based fuels. Spark-ignition (SI) engines are suitable for converting the chemical energy of syngas for small-scale electrical power generation. However, syngas-fueled SI engines have lower power outputs and thermal efficiencies than SI engines fueled with conventional fuels such as gasoline and natural gas do. The objective of this study was to compare the stoichiometric and lean combustion modes in a single-cylinder SI engine to determine the optimal combustion mode for the development of a syngas engine generator with high power and high efficiency. A high gross indicate power was achieved in the stoichiometric combustion mode by increasing the intake pressure, owing to the increase in the volumetric efficiency and syngas fuel input. The gross indicated thermal efficiency (ITE) improved as the compression ratio was increased from 10:1 to 17.1:1, owing to the high peak heat release rate and short combustion duration. In the lean combustion mode, high gross ITEs were achieved by increasing the excess air ratio to 2.5, but the additional increase led to low combustion efficiencies. However, the gross indicated power decreased with an increase in the excess air ratio. The low gross indicated power was increased through intake boosting. Based on a parametric study, the optimal compression ratio for the stoichiometric combustion mode was selected to be 15:1. Pre-ignition occurred in the stoichiometric combustion mode at a compression ratio of 17.1:1 and an intake pressure of 0.16 MPa. Engine operation with a high compression ratio of 17.1:1 was possible in the lean combustion mode owing to the low combustion temperature. The gross ITE in the lean combustion mode was 18.4% higher than that in the stoichiometric combustion mode, mainly because of a significant reduction in the heat transfer loss. However, the gross indicated power in the lean combustion mode was 25.6% lower than that in the stoichiometric combustion mode.

Spatiotemporal flame propagations, combustion and solid particle emissions from lean and stoichiometric gasoline direct injection engine operation

Increased particle number and mass emissions in gasoline direct injection (GDI) engines should require to investigate in-cylinder flame and combustion characteristics associated with primary source of particle emissions. In this work, in-cylinder spatiotemporal flame luminosity is quantitatively characterized to features combustion process and solid particle emissions from a GDI engine operating in two lean and one stoichiometric modes. Low- and high-steady state operating points were used to compare combustion strategies on flame development and emission characteristics. A fiber-optic sensor composed of eight measurement channels detected the flame front and the direction of the flame propagation in the combustion chamber. Solid particle emissions in the exhaust were measured using an engine exhaust particle sizer and a micro soot sensor. Results of the experiments showed that two lean combustion modes by injection strategies resulted in distinct combustion and flame development. Lean combustion modes generated high diffusion flame by burning stratified rich-mixture. Although the lean cases resulted in strong diffusion flames, the lean-homogeneous produced similar particle size distributions with the stoichiometric mode with high ash particles. Piston pool fires on the piston surface in the lean-stratified mode induced a large accumulation mode with high particle mass concentrations.

Effects of mixture enleanment in combustion and emission parameters using a flex-fuel engine with ethanol and gasoline

The growing global energy demand, the fossil fuel depletion and increasing CO2 and pollutant emissions in arising from human activities are increasingly impacting the economy and government measures. For this reason, the automotive industry is constantly in search for new and environment friendly technologies and strategies, such as the use of biofuels and the variation in air-fuel ratio. These strategies have already been vastly studied, but few studies were conducted with ethanol. Thereby, this paper aims to analyze and compare the effects of ethanol and gasoline mixture enleanment in a flex-fuel engine in terms of performance, emissions and combustion. For this, it was evaluated how indicated specific fuel consumption (ISFC), emissions and combustion patterns are affected when using both Brazilian commercial gasoline (E27) and hydrous ethanol (E96) in lean conditions. The results show similar combustion parameter behavior for both fuels, pointing to ISFC reduction when operating in lean combustion modes of more than 5% and 12% for ethanol and gasoline, respectively. Despite the lower thermal and fuel conversion efficiencies resulting from the smaller Lower Heating Value (LHV), the advantage of the biofuel appears in the emission analysis. For both fuels, lean combustion results in virtual elimination of carbon monoxide (CO) emission, decreasing of 89% in nitrogen oxides (NOx) for ethanol and 74% for gasoline. Added to this, ethanol’s combustion results in lower HC emission, highlighting the potential of this biofuel.

A comparative study of lean burn and exhaust gas recirculation in an HCNG-fueled heavy-duty engine

Two dilution strategies, exhaust gas recirculation (EGR) with a stoichiometric mixture and excess air with a lean mixture, were investigated for an 11 L, 6-cylinder H2-blended compressed natural gas (HCNG) engine. The engine was operated at 1260 rpm and 50% of maximum engine load (575 Nm) at maximum brake torque for each strategy. To evaluate the EGR approach, the stoichiometric combustion mode was varied, and to evaluate the lean combustion mode, the excess air ratio was varied. The maximum EGR rate and lean flammability limit were constrained by the combustion stability. The dilution rate was employed to compare the dilution effect on engine performance and emission levels under identical levels of the dilution for both combustion modes. The thermal efficiencies under stoichiometric combustion with EGR were lower than those under lean combustion, owing to a higher pumping loss and a lower combustion speed. The total hydrocarbon emissions under the lean combustion mode were lower than those under the stoichiometric combustion mode only when the combustion speed was relatively slow, due to the higher mixing rate caused by the active combustion. As the dilution rate was increased in the lean combustion mode, the rate of decrease in NOx emissions slowed compared to the stoichiometric combustion mode. The lowest level of engine-out NOx emissions was observed under lean combustion.

Mild HEV with Multimode Combustion: Benefits of a Small Oxygen Storage

This simulation study discusses the application of a multimode combustion engine in a mild hybrid electric vehicle (HEV) with three-way catalytic converter (TWC). Operation in the lean combustion mode homogeneous charge compression ignition (HCCI) results in oxidation of the oxygen storage capacity (OSC) of the TWC. Thereby, the TWC’s ability to convert NOx under lean conditions is removed. Succeeding depletion of the OSC under rich spark-ignition (SI) conditions is required, which results in significant fuel efficiency penalties. In case of a mild HEV the torque assist from the electric motor is able to extend the residence time in HCCI, thereby reducing the number OSC depletion events. The applied supervisory controller, which decides when to switch between SI and HCCI, is based on the equivalent consumption minimization strategy (ECMS) and incorporates the fuel penalties associated with mode switching and OSC depletion. It is shown that, while the impact of the OSC depletion on drive cycle fuel economy of the mild HEV is still significant, it is much smaller than in case of the vehicle without electric motor. The prolonged operation in lean HCCI mode leads to substantial amounts of tailpipe NOx for all drive cycles tested. In a case study two modifications to the system hardware are introduced with counterintuitive results. First, the HCCI regime is further constrained to conditions where engine-out NOx levels are extremely low. Second, the size of the OSC is significantly reduced, allowing a much faster and less inefficient depletion. Associated drive cycle results show a substantial reduction in tailpipe NOx while fuel economy benefits can be maintained.