Natural Gas Spark Ignition Research Articles

Increasing Efficiency and Reducing Emissions in a Small Displacement Gasoline Engine With Hydrogen-Enriched Natural Gas

Abstract There is currently a gap in the available literature on retrofitting engines with less-advanced control systems to run on hydrogen-enriched natural gas. Potential advantages of hydrogen-enriched natural gas in these engines may not be realized without altering parameters such as spark-timing, exhaust gas recirculation, or the air/fuel ratio. However, in such engines, changes in spark-timing and exhaust gas recycle are often cost-prohibitive, leaving equivalence ratio adjustments as one of the few remaining viable operational strategies. In this study, a small-displacement (319 cc), naturally aspirated, single-cylinder gasoline engine without spark-timing control was converted to run on a 10 vol% blend of hydrogen-enriched natural gas. Stoichiometric operation improved thermal efficiency, fuel consumption, and total hydrocarbon emissions, but higher NOx emissions resulted. Despite no spark-timing control, lean-burn operation at an equivalence ratio of 0.7 was found to maintain performance improvements while also lowering emissions: fuel consumption was lowered versus the methane base case by 11%, and NOx and hydrocarbon emissions were both decreased by approximately 70% below the base case. This study concludes that in a scenario even without spark-timing control, the addition of 10 vol% hydrogen can improve power, emissions, and efficiency of a spark-ignited natural gas engine, which serves as a proof-of-concept that even fairly simple, small-displacement engines can benefit from switching from gasoline to hydrogen-enriched natural gas operation.

Neat ammonia use in a heavy-duty diesel engine converted to spark ignition focused on lean operation

Neat ammonia use in a heavy-duty diesel engine converted to spark ignition focused on lean operation

Investigating the Effect of Ammonia Addition on the Performance of a Heavy-Duty Natural Gas Spark Ignition Engine Operated at Stoichiometric Conditions

Abstract Due to the pressing issue of global warming, there has been a significant focus on zero- and low-carbon fuels globally. Among hydrocarbon fuels, methane is widely used in spark ignition engines due to its abundance and relatively low carbon footprint. However, to further reduce carbon emissions, interest is growing in the use of ammonia, a zero-carbon fuel, as a partial replacement for methane. Consequently, it is crucial to investigate the impact of ammonia addition on the performance of natural gas spark ignition engines. A key challenge in studying ammonia-methane engines is that the introduction of ammonia alters the formation mechanisms of nitrogen-based pollutants, resulting in the coupling of fuel-borne and air-borne nitrogen pollutants. As a result, research on the nitrogen-based emissions of ammonia-methane engines has been limited. This study addresses this issue by differentiating between atmospheric nitrogen and fuel nitrogen elements, effectively decoupling fuel-borne and air-borne nitrogen pollutants. This approach provides valuable insights into the effects of ammonia addition on the nitrogen-based pollutant characteristics of natural gas engines. The results indicate that ammonia addition introduces N2O, a species absent in pure methane engines. The N2O primarily originates from cold wall regions and the partial oxidation of ammonia released from engine crevices during the late oxidation process. Although NO remains the dominant nitrogen-based pollutant and the amount of N2O is small, the significant greenhouse gas potential of N2O warrants further attention. Furthermore, while ammonia addition increases the NO concentration in the burning zone, it slightly reduces the NO concentration at chemical equilibrium under stoichiometric conditions. As a result, engines operating with an ammonia energy substitution ratio of 0.4 exhibit lower NOx emissions compared to those fueled solely by methane. These findings underscore the need for further research into the combustion and emission characteristics of ammonia-methane spark ignition engines.

Effects of charge motion on knock and thermal efficiency under high load condition of a heavy-duty natural gas engine

Nowadays, the carbon-neutral trend and the crude oil crisis have brought natural gas into increasing focus. However, heavy-duty engines fueled by natural gas have been plagued by thermal efficiency and knocking limitation problems. Well-structured charge motions can enhance thermal efficiency and concurrently mitigate knock, however, there is a lack of comprehensive work involving charge motions. In this paper, numerical simulation is employed to investigate the impact of charge motion on knock and thermal efficiency under high load conditions for a heavy-duty spark-ignition natural gas engine. The findings indicate that in the configuration with intense swirl, the diminished turbulent kinetic energy (TKE) at the combustion chamber’s base lessens the convective heat exchange between the fresh charge and the heated exhaust gases, resulting in a noticeable high-temperature zone and triggering hot spots. In configurations with inclined swirl and strong tumble motion, the extensive tumble motion near the spark plug region close to top dead center leads to an asymmetric flame front shape, determining the location of hotspots. The research also revealed that excessive tumbling motion and TKE can increase the likelihood of engine knock, while appropriate cylinder charge motion can improve the knock resistance of the engine to some extent, the maximum reduction in knocking intensity can reach 92.5%. The optimized combustion systems can significantly improve the initial combustion rate, shorten the ignition delay period, and advance the combustion center. With the combined effects of ignition timing and charge motion, the total indicated specific power per unit of fuel mass is increased in the optimized systems. Compared to the original combustion system, the indicated thermal efficiency within the knocking boundary can be improved by 1.11%.

Evaluating potential of increasing flow intensity and reducing crevice volume to improve thermal efficiency and hydrocarbon emission in spark-ignition natural gas engines

Evaluating potential of increasing flow intensity and reducing crevice volume to improve thermal efficiency and hydrocarbon emission in spark-ignition natural gas engines

Performance, emissions and combustion analysis of hydrogen-enriched compressed natural gas spark ignition engine by optimized Gaussian process regression and neural network at low speed on different loads

Performance, emissions and combustion analysis of hydrogen-enriched compressed natural gas spark ignition engine by optimized Gaussian process regression and neural network at low speed on different loads

Feasibility and Performance Analysis of Cylinder Deactivation for a Heavy-Duty Compressed Natural Gas Engine

The rising interest in the use of gaseous fuels, such as bio-methane and hydro-methane, in Heavy-Duty (HD) engines to reduce Greenhouse Gases pushed by the net-zero CO2 emissions roadmap, introduced the need for appropriate strategies in terms of fuel economy and emissions reduction. The present work hence aims at analysing the potential benefits derived from the application of the cylinder deactivation strategy on a six-cylinder HD Natural Gas Spark Ignition (SI) engine, typically employed in buses and trucks. The activity stems from an extensive experimental characterisation of the engine, which allowed for validating a related 1D model at several Steady-State conditions over the entire engine workplan and during dynamic phases, represented by the World Harmonized Transient Cycle (WHTC) homologation cycle. The validated model was exploited to assess the feasibility of the considered strategy, with specific attention to the engine working areas at partial load and monitoring the main performance parameters. Moreover, the introduction in the model of an additional pipeline and of valves actuated by a dedicated control logic, allowed for embedding the capability of using Exhaust Gas Recirculation (EGR). In the identified operating zones, the EGR strategy has shown significant benefits in terms of fuel consumption, with a reduction of up to 10%. Simultaneously, an appreciable increase in the exhaust gas temperature was detected, which may eventually contribute to enhance the Three-Way Catalyst (TWC) conversion efficiency. Considering that few efforts are to be found in the literature but for the application of the cylinder deactivation strategy to Light-Duty or conventionally fuelled vehicles, the present work lays the foundation for a possible application of such technology in Natural Gas Heavy-Duty engines, providing important insights to maximise the efficiency of the entire system.

Combustion Process of the Compound Supply CNG Engine

Objective: In order to study the lean combustion process of a natural gas engine by separating the combustor, a spark ignition natural gas engine with separated combustors was retrofitted from a S195 single-cylinder diesel engine. Methods: The electronic control system controlled the gas supply and the spark plug ignition. A low pressure injection valve was set in the inlet pipe to form a lean mixture while a high pressure injection valve was placed in the subsidiary chamber to create a rich mixture, which was then ignited and injected into the main combustor, where the lean mixture was subsequently ignited again to achieve stratified combustion. Results: The test results showed that steady ignition is feasible in the system and verified the impact of the shape of the main combustor on HC, the impact of channel diameter on NOX production, and the impact of the ratios of high-pressure gas and low-pressure gas on HC and NOX. The combustion conditions of high-pressure gas and low-pressure gas in the engine combustor vary greatly. Our results signify that the shape of the main combustor has a great impact on the performance of the engine, that is, a shorter propagation distance can reduce the generation of HC. Conclusion: The best ignition advance angle under different conditions was determined using a spark ignition natural gas engine. The ratios of high-pressure gas and low-pressure gas greatly impact the performance and emission of the engine. The reduced diameter of the channels between the main and subsidiary combustors can enhance the stratification and facilitate the secondary ignition.

Study on hydrogen substitution in a compressed natural gas spark-ignition passenger car engine

Hydrogen substitution in applications fueled by compressed natural gas arises as a potential alternative to fossil fuels, and it may be the key to an effective hydrogen economy transition. The reduction of greenhouse gas emissions, especially carbon dioxide and unburned methane, as hydrogen is used in transport and industry applications, makes its use an attractive option for a sustainable future. The purpose of this research is to examine the gradual adoption of hydrogen as a fuel for light-duty transportation. Particularly, the study focuses on evaluating the performance and emissions of a single-cylinder port fuel injection spark-ignition engine as hydrogen is progressively increased in the natural gas-based fuel blend. Results identify the optimal conditions for air dilution and engine operation parameters to achieve the best performance. They corroborate that the dilution rate has to be adjusted to control pollutant emissions as the percentage of hydrogen is increased. Moreover, the study identifies the threshold for hydrogen substitution below which the reduction of carbon dioxide emissions due to efficiency gains is negligible compared to the reduction of the carbon content in the fuel blend. These findings will help reduce the environmental footprint of light-duty transportation not only in the long term but also in the short and medium terms.

A Review of Ultra-lean and Stratified Charged Combustion in Natural Gas Spark Ignition Engines

A Review of Ultra-lean and Stratified Charged Combustion in Natural Gas Spark Ignition Engines

Exergy Analysis of Organic Rankine Cycles with Zeotropic Working Fluids

Waste heat recovery is one of the possible solutions to improve the efficiency of internal combustion engines. Instead of wasting the exhaust stream of an energy conversion system into the environment, its residual energy content can be usefully recovered, for example in Organic Rankine Cycles (ORC). This technology has been largely consolidated in stationary power plants but not yet for mobile applications, such as road transport, due to the limitations in the layout and to the constraints on the size and weight of the ORC system. An ORC system installed on the exhaust line of a bus powered by a natural gas spark ignition engine has been investigated. The thermal power available at engine exhaust has been evaluated by measuring gas temperature and mass flow rate during real driving operation. The waste thermal power has been considered as heat input for the ORC plant simulation. A detailed heat exchanger model has been developed because it is a crucial component for the ORC performance. The exergy analysis of the ORC was performed comparing different working fluids: R601, R1233zd(E) and two zeotropic blends of the two organic pure fluids. The model allowed the evaluation of the ORC produced energy over the driving cycle and the potential benefit on the engine efficiency.

Effects of low-grade gas composition on the energy/exergy performance of a polygeneration system (CH 2 HP) based on biomass gasification and ICE

Bio-hydrogen from sustainable biomass (i.e. agro-industrial residues) gasification can play a relevant role in the hydrogen economy, providing constant hydrogen from renewable sources. Nowadays, most hydrogen production systems integrate one or more water-gas shift (WGS) units to maximize the hydrogen yield that, however, needs additional syngas treatments, investment and operational costs. Besides, different electricity inputs are needed along the process to power the compression of raw syngas, shifted syngas, and pure hydrogen to the desired pressure. This common process integration with WGS generates a kind of off-gas from the hydrogen separation unit whose composition may or may not be suitable for power production, depending on the operating conditions of the gasification unit. In this regard, this work proposes a different approach in which no WGS reactors are involved and the off-gas is used to generate heat and power to provide the energy input needed by the system. In particular, the authors tested the bio-syngas and the corresponding off-gas in a 4-cylinders, spark ignition natural gas internal combustion engine operated in cogeneration mode with the aim to analyse the effect of removing the hydrogen from the original bio-syngas on mechanical/electric and thermal power, on fuel efficiency and CO2 specific emission.

Influence of Intake Port Structure on the Performance of a Spark-Ignited Natural Gas Engine

Spark-ignited natural gas engines have received increasing attention in the heavy-duty market due to their low cost and reliability advantages. However, there are still some issues with natural gas engines retrofitted from 10 to 15 L diesel engines, which is a valuable medium-term goal for the automotive industry. In this work, the effect of intake port structure on the performance of a spark-ignited heavy-duty natural gas engine was investigated by multidimensional numerical simulations. A newly designed intake port was proposed, with strengthened in-cylinder turbulent kinetic energy and homogeneous air-fuel mixtures. Bench tests show that the proposed intake port has impressive thermal efficiency, cycle variation, and acceptable emissions performance. The effective thermal efficiency improves from 41.0% to 41.4%, and the cycle variation is 36% lower than traditional schemes. However, with the accelerated flame propagation, the in-cylinder temperature and NOx emission of the mixed-flow port increase while the CO emission decreases. In summary, a proper balance of in-cylinder swirl and tumble flow can significantly affect the economy and stability of natural gas engines. The proposed structure solves the inherent problems of slow natural gas flame propagation and harmful cyclic variations.

Multi-scale dynamics for a lean-burn spark ignition natural gas engine under low load conditions

• The multi-scale dynamic characteristics are studied. • The gas injection timing is used as the impact factor. • The IMEP time series have multi-scale periodic oscillation characteristics. • The combustion status between 2 and 8 engine cycles has a certain degree of correlation. This work investigates the multi-scale dynamics of the combustion system in a lean-burn spark ignition natural gas engine using different gas injection timings (GIT). The in-cylinder pressure time series are measured, and the indicated mean effective pressure (IMEP) time series are calculated. The influence of GIT on the combustion system is investigated through wavelet analysis, multi-resolution analysis, and the return maps with the GIT covering from 0 to 90°CA after top dead center at the intake stage. Results show that the combustion system has multi-scale chaotic characteristics, and it is sensitive to the change of GIT. The unreasonable GIT will result in serious combustion variations. Meanwhile, the combustion instability of the engine evolves on multiple time scales, showing evident multi-scale oscillation characteristics. All the wavelet power spectrums (WPS) present the characteristics of intermittent short-time periodic oscillations and persistent large-scale periodic oscillations concealed inside the IMEP time series. When the GIT approaches the medium value, the persistence of large-scale periodic oscillations is weakened, while the characteristics of high-frequency intermittent oscillations are enhanced. Under all working conditions, the contribution rate of high-frequency signal D 1 decomposed by the IMEP time series to the overall time series fluctuation is about 40% or even higher. The contribution rate of the signal D 1 also increases with the aggravation of combustion instability. The return map structures of high-frequency signals D 1 and D 2 show bifurcation structures, and the bifurcation characteristics of the signal D 1 are more evident under medium GIT conditions, indicating a certain correlation between the 2–8 engine cycles, and the correlation between the adjacent engine cycles is stronger. The deterministic relationship between the multiple engine cycles found can help in developing a more reasonable and efficient combustion control strategy, which provides a theoretical basis for improving the stability of a natural gas engine.

Numerical Investigation of the Effects of Engine Speed on Performance and Combustion Characteristics on a Converted Spark-Ignition Natural Gas Engine

In this study, the effects of different engine speed values on performance and combustion characteristics were investigated by converting a diesel engine to a spark-ignition engine using natural gas. In numerical analysis, G-equation combustion model, reduced methane chemical kinetic mechanism that represent natural gas consisting of 29 types and 171 equations, and RANS k-e turbulence model were used. Analyzes were performed at full load, 17.5:1 compression ratio, constant ignition timing, and 6 different engine speeds. In order to examine only the effect of speed, the initial value, boundary conditions and spark plug ignition time were considered constant. While engine power and fuel consumption increased with increasing engine speed, engine efficiency decreased. In addition, increasing engine speed also increased the ignition delay time and combustion duration, and the flame front reached the squish zone later.

Optical and Numerical Investigation of Flame Propagation in a Heavy Duty Spark Ignited Natural Gas Engine With a Bowl-in-Piston Chamber

Abstract Increasing the natural gas (NG) use in heavy-duty engines is beneficial for reducing greenhouse-gas emissions from power generation and transportation. However, converting compression ignition (CI) engines to NG spark ignition operation can increase methane emissions without expensive aftertreatment, thereby defeating the purpose of utilizing a low carbon fuel. The widely accepted explanation for the low combustion efficiency in such retrofitted engines is the lower laminar flame speed of natural gas. In addition, diesel engine's larger bowl size compared to the traditional gasoline engines increases the flame travel length inside the chamber and extends the combustion duration. Optical measurements in this study suggested a fast-propagating flame developed even at extremely lean operation. A three-dimensional numerical simulation showed that the squish region of the bowl-in-piston chamber generated a high turbulence intensity inside the bowl. However, the flame propagation speed reduced by 55% when transiting from the bowl to the squish region, due to the large decrease in turbulence intensity inside the squish region. Moreover, the squish volume trapped an important fuel fraction, which experienced a slow and inefficient burning process during the expansion stroke. This resulted in increased methane emissions and reduced combustion efficiency. Overall, it was the specifics of the combustion inside a bowl-in-piston chamber not the methane's slow laminar flame speed that contributed to the low methane combustion efficiency for the retrofitted engine. The results suggest that optimizing the chamber shape is paramount to boost engine efficiency and decrease its emissions.

Parallel perturbation analysis of combustion cycle-to-cycle variations and emissions characteristics in a natural gas spark ignition engine with comparison to consecutive cycle method

Severe combustion cycle-to-cycle variations (CCVs) in spark ignition (SI) engines significantly increase partial or incomplete combustion cycles, which may result in combustion instability or even misfire under extreme conditions, thereby seriously affecting the engine performance and increasing the unburned hydrocarbon and carbon monoxide emissions. In this study, the consecutive cycle method (CCM) and parallel perturbation method (PPM) are utilized to simulate the CCVs in a natural-gas (NG) SI engine. Specifically, 25 consecutive and concurrent cycles of the SI engine are simulated, and simulation results are compared with the experimental data. Further, the factors affecting the CCVs and exhaust emissions in the NG SI engine are verified by analyzing the low-pressure (LP) and high-pressure (HP) cycles. The results indicate that the simulated in-cylinder pressures of the NG SI engine based on PPM are basically in agreement with the experimental in-cylinder pressure distribution range, which suggests that the PPM can effectively predict the CCVs in NG SI engines. Furthermore, the required wall clock time for the simulation of CCVs is greatly reduced from 1 to 2 months (using CCM) to 2-3 days by using the PPM, which makes it particularly suitable for the industrial applications. Besides, the velocity field of the HP cycle is obviously stronger than that of the LP cycle. During the early stage of flame development, the flame area and volume of LP and HP cycles do not show much difference. However, the flame front surface-volume ratio of the HP cycle is larger than that of the LP cycle at 15 CA after the spark timing. Furthermore, the emissions formation and oxidation of the NG SI engine are strongly depended on the HP and LP cycles due to the combustion rate and flame propagation in the cylinder.

Investigations on combustion system optimization of a heavy-duty natural gas engine

• Two intake ports and four combustion chambers were studied on spark ignition natural gas engines. • Optimized chemical model was used for computation acceleration while keeping accuracy. • Effective mixed-flow intake ports were proposed to improve the in-cylinder turbulence. • Eccentric hemispherical combustion chamber scheme with mixed intake flow showed the most optimal combustion performance. • Eccentric hemispherical combustion chamber scheme exhibited increased NO x emissions while negligible CO and CH 4 emissions. Nowadays, the carbon-free policies and the crisis of crude oil make natural gas get increasing attention. However, spark-ignited natural gas engines continually suffer from problems of thermal efficiency and NO x emissions. Optimizing intake and combustion systems are effective ways to improve combustion and emission performance, but comprehensive work involving both intake and combustion systems is still lacking, especially for heavy-duty commercial engines. In this work, both intake and combustion systems of spark-ignited heavy-duty natural gas engines were investigated using muti-dimensional numerical simulations. Two intake ports and four combustion chambers were considered. An optimized chemical model was employed to accelerate the computation efficiency of combustion processes. The optimal combination of intake and combustion systems was obtained, with impressive thermal efficiency and acceptable emission performance. The results show that the mixed-flow intake port performs better than the swirl intake port for the natural gas engine with premixed combustion mode, manifesting increased in-cylinder tumble ratio and turbulent kinetic energy. Meanwhile, the eccentric hemispherical combustion chamber (EHCC) combined with mixed-flow intake ports presents the best optimal combustion performance, exhibiting an effective thermal efficiency beyond 41.53%. However, the EHCC scheme shows an increased NO x emission due to fast combustion speed and high combustion temperature while negligible CO and CH 4 emissions. Despite this, natural gas engines equipped with three-way catalysis after-treatment can still meet emission regulations under stoichiometric operating conditions.

An Evaluation of the Conversion of Gasoline and Natural Gas Spark Ignition Engines to Ammonia/Hydrogen Operation From the Perspective of Laminar Flame Speed

Abstract Power generation systems will reduce carbon emissions primarily through the application of low or even zero carbon fuels under the global decarbonization trend. Ammonia is an ideal alternative fuel because it is cheap, readily available, and easy to store and transport. However, its mediocre combustion performance has raised concerns about its use in engines. The objective of this paper was to evaluate the amount of hydrogen that would need to be added to the ammonia from a laminar flame speed perspective if converting existing spark ignition engines to ammonia operation. The benchmark for determining the hydrogen blending ratio was to help ammonia achieve efficient combustion in the cylinder comparable to that of gasoline or natural gas. The results showed that hydrogen addition had the potential to greatly improve engine efficiency and emissions, although the combustion kinetics of ammonia-hydrogen mixtures were still dominated by ammonia with hydrogen addition levels below 60%. In addition, the hydrogen addition ratio was mainly determined by the kernel inception process, as this burning stage heavily influenced the repeatability of the combustion and the ease of combustion control. Also, at least 20% of hydrogen was required to be added to ammonia to adapt the engine to various operating conditions, while such a strategy still cannot help ammonia to obtain a rapid burning event compatible with gasoline or methane. Moreover, natural gas engines were more suitable for retrofitting to ammonia-hydrogen operation because they have a higher compression ratio and their combustion chambers are less demanding on the fuel laminar flame speed. Further, ammonia lean operation was recommended to be avoided in spark ignition configurations. Altogether, all of these findings support the need for additional efforts in ammonia engine optimizations and onboard ammonia dissociation system efficiency improvements.

Spark-Induced Breakdown Spectroscopy In A Direct-Injected Natural Gas Spark-Ignition Engine

The purpose of this study is to investigate the fuel concentration around the spark plug obtained using spark-induced breakdown spectroscopy (SIBS) method with the spark plug with an optical fiber in the direct-injected natural gas SI engine. Effect of exposure duration on measurement accuracy of fuel concentration was discussed. Equivalence ratio around the spark plug in the direct-injected natural gas SI engine were measured under different natural gas injection timing. When the exposure duration is shortened, the emission of potassium elements near the emission wavelength of oxygen elements can be suppressed, and the measurement accuracy in the calculation of the emission intensity ratio can be improved. The relationship between the luminescence intensity ratio of hydrogen and oxygen (Hα/O) and the equivalence ratio of homogeneous mixture of natural gas and air was investigated and it was found that there was a positive correlation between the luminescence intensity ratio of hydrogen and oxygen (Hα/O) and the equivalence ratio. As a result of measuring the equivalence ratio around the spark plug of direct-injected natural gas SI engine using the SIBS method, an equivalence ratio of 0.67 was measured for a set value of 0.8 using the luminescence intensity ratio of hydrogen and oxygen.