Experimental investigation of varying composition of HCNG on performance and combustion characteristics of a SI engine

With rapid depletion of petroleum resources, researchers are investigating alternate fuels to meet global transportation energy demand. Gaseous fuels such as compressed natural gas (CNG) and hydrogen are of special interest because of their cleaner combustion characteristics compared to liquid petroleum based fossil fuels. However both these gaseous fuels have some technical issues when they are used as stand-alone alternate fuel in conventional spark ignition (SI) engines. CNG suffers from lower energy density and narrow flammability range whereas backfiring tendency is highly pronounced in hydrogen fueled engines. Hydrogen enriched compressed natural gas (HCNG) mixtures are observed to be good alternative to these individual fuels since these mixtures do not pose the issues experienced by the constituent fuels i.e. CNG and hydrogen. In this study, experiments were conducted in a spark ignited gas engine using various compositions of HCNG mixtures having 0, 10, 20, 30, 50, 70 and 100% (v/v) hydrogen fraction. The performance and combustion characteristics of these test fuels were compared with that of baseline CNG, in order to find an optimum HCNG mixture composition for a single cylinder gas engine. Results obtained showed that 30HCNG mixture delivered superior engine performance compared to other HCNG mixtures and baseline CNG, which is in sharp contrast to 15HCNG being advocated globally.     

Particulate characteristics of laser ignited hydrogen enriched compressed natural gas engine

Laser ignition (LI) is emerging as a strong technology to control the oxides of nitrogen (NOx) emissions from spark ignition (SI) engines without the need for any significant exhaust gas after-treatment and is an appropriate technology for meeting future emission norms in the automotive sector. In this study, particulate characteristics of LI engine fuelled with different compressed natural gas (CNG) and hydrogen mixtures [100% CNG, 10HCNG (10% v/v hydrogen with 90% v/v CNG), 30HCNG (30% v/v hydrogen with 70% v/v CNG), 50HCNG (50% v/v hydrogen with 50% v/v CNG) and 100% hydrogen] were investigated. Experiments were performed in a suitably modified single cylinder engine, which operated in LI mode at constant engine speed (1500 rpm) at five different engine loads (5, 10, 15, 20 and 25 Nm). Particulate characteristics were determined using an engine exhaust particle sizer (EEPS). Results showed that particle number concentration increased with increasing engine load. Number-size, surface area-size and mass-size distributions of particulates reflected that addition of hydrogen in the CNG improved particulate emission characteristics especially in nucleation mode particle (NMP) size range (10 nm < Dp < 50 nm). Among the test fuels, hydrogen-fuelled engine emitted the lowest number of particles. It was observed that the difference between particulate characteristics emitted by different test fuels reduced at higher engine loads. Significant contribution of lubricating oil in particulate emissions from both hydrogen as well as HCNG fuelled LI engine was an important finding of this study. Dominant contribution of larger particles (Dp > 50 nm) in total particle mass (TPM) was an important observation of this study. The qualitative correlation between total particle number (TPN) and TPM indicated that suitable fuel composition at different engine loads yielded cleaner exhaust from the LI engine. Overall, this study demonstrated that addition of hydrogen in CNG is advantageous from particulate reduction point of view, however, optimum fuel composition should be adjusted according to engine operating condition in order to reduce particulate emissions.     

Emissions and fuel consumption characteristics of an HCNG-fueled heavy-duty engine at idle

The idle performance of an 11-L, 6-cylinder engine equipped with a turbocharger and an intercooler was investigated for both compressed natural gas (CNG) and hydrogen-blended CNG (HCNG) fuels. HCNG, composed of 70% CNG and 30% hydrogen in volume, was used not only because it ensured a sufficient travel distance for each fueling, but also because it was the optimal blending rate to satisfy EURO-6 emission regulation according to the authors' previous studies. The engine test results demonstrate that the use of HCNG enhanced idle combustion stability and extended the lean operational limit from excess air ratio (λ) = 1.5 (CNG) to 1.6. A decrease of more than 25% in the fuel consumption rate was achieved in HCNG idle operations compared to CNG. Total hydrocarbon and carbon monoxide emissions decreased when fueled with HCNG at idle because of the low carbon content and enhanced combustion characteristics. In particular, despite hydrogen enrichment, less nitrogen oxides (NO_x) were emitted with HCNG operations because the amount of fuel supplied for a stable idle was lower than with CNG operations, which eventually induced lower peak in-cylinder combustion temperature. This low HCNG fuel quantity in idle condition also induced a continuous decrease in NO_x emissions with an increase in λ. The idle engine test results also indicate that cold-start performance can deteriorate owing to low exhaust gas temperature, when fueled with HCNG. Therefore, potential solutions were discussed, including combustion strategies such as retardation of spark ignition timing combined with leaner air/fuel ratios.     

On road experimental tests of hydrogen/natural gas blends on transit buses

The promise of reducing harmful and CO₂ emissions by focusing on hydrogen-methane blends (HCNG) have recently attracted the interest of vehicle manufacturers and transport operators. Several experiments have been conducted in laboratory facilities to assess the potential of HCNG blends in order to decrease the exhaust emissions. This paper reports the results of experimental tests performed at the ENEA Casaccia Research Center aiming to evaluate the energy and environmental performances of a CNG vehicle when fuelled with a hydrogen-methane blend. Two buses for urban transit service were fuelled with HCNG blends with different percentage of hydrogen (5%, 10%, 15%, 20% and 25% of hydrogen by volume). A 100% methane gas was used as reference to compare the advantages and disadvantages that can be derived from the use of HCNG blends. Road tests have been carried out by running fixed tracks, which are representative of urban and suburban driving cycles. Vehicles were powered with a lean burn engine whose setup - based on ignition advance angle, has been tuned for controlling the NO_x emissions. CO₂ emissions have been investigated to evaluate the leverage effect based on an increased CO₂ reduction resulting from an increased engine efficiency.     

Performance and emission assessment of a multi-cylinder S.I engine using CNG & HCNG as fuels

The present study was carried out to assess the possibility of using the HCNG in the commercially available CNG vehicles, as the available literature indicated the benefits of adding hydrogen to CNG in small percentages by volume, leading to improved combustion characteristics of CNG and yielding sizeable benefits, regarding improved engine performance and reduced engine emissions in automotive applications. In the present study, a commercially available CNG manifold carburation kit, commonly known as “sequential injection” in the market, is evaluated for its operation characteristics, on a Spark Ignited (SI), MPFI automotive engine, of a mass-produced passenger vehicle, converted for gas operation, using, gasoline, CNG, HCNG 10% and HCNG 18% as fuels. In the study, the following performance parameters, torque, power, thermal efficiency, brake specific energy consumption (BSEC), lambda, engine oil temperature, exhaust gas species were measured. After exhaustive engine testing, a comparison of engine performance emission characteristics for gasoline, CNG and HCNG 10% and HCNG 18% is presented. The engine performance using the optimized MAP tables demonstrated torque and power improvements for HCNG 10% and HCNG 18% in comparison to CNG. The torque benefits up-to 6% and power benefits up-to 4% were observed. The fuel energy consumption was measured to be reduced, and improvement in fuel conversion efficiency was also observed. Hydrogen substitution in CNG helped in reducing CO, HC, CO₂ emissions for HCNG in comparison to CNG. Increase in NO_x emission was observed for HCNG in comparison with CNG. Superior engine emission characteristics in comparison to gasoline and CNG is also demonstrated. The commercially available sequential gas manifold carburation was found to be suitable for HCNG 10% and HCNG 18%.     

Experimental study of hydrogen enriched compressed natural gas (HCNG) engine and application of support vector machine (SVM) on prediction of engine performance at specific condition

The effect of excess air ratio (λ) and ignition advance angle (θ_ig) on the combustion and emission characteristics of hydrogen enriched compressed natural gas (HCNG) on a 6-cylinder compressed natural gas (CNG) engine has been experimental studied in an engine test bench, aiming at enriching the sophisticated calibration of HCNG fueled engine and increasing the prediction accuracy of the SVM method on automobile engines. Three different fuel blends were selected for the experiment: 0%, 20% and 40% volumetric hydrogen blend ratios. It is noted that combustion intensity varies with the excess air ratio and the ignition advance angle, so are the emissions. The optimal value of λ or θ_ig has been explored in the specific engine condition. Results show that blending hydrogen can enhance and advance the combustion and stability of CNG engine, and it also has some benefic influence on the emissions such as reducing the CO and CH₄. Meanwhile, a simulation research on forecasting the engine performance by using the support vector machine (SVM) method was conducted in detail. The torque, brake specific fuel consumption and NO_x emission have been selected to characterize the power, economic and emissions of the engine with various HCNG fuels, respectively. It can be seen that the optimal model built by the SVM method can highly describe the relationship of the engine properties and condition parameters, since the value of the complex correlation coefficient is larger than 0.97. Secondly, the prediction performance of the optimal model for torque or BSFC is much better than the case of NO_x. Besides, the optimal model built by the PSO optimization method has the best prediction accuracy, and the accuracy of the model obtained based on the training group with 20% hydrogen blend ratio is the best compared with those of others. The upshots in this article provide experimental support and theoretical basis for the adoption of HCNG fuel on internal combustion engines as well as the application of intelligent algorithmic in the engine calibration technology field.     

Techno-economic review assessment of hydrogen utilization in processing the natural gas and biofuels

The automobile sector dominated by conventional fossil fuels greatly impacted human lives and strengthened the economy of many countries. However, the harmful emissions from the engines have contaminated the environment and induced severe climate changes; hence the emphasis is being laid on low carbon fuels that emit lower emissions and greenhouse gases. In this regard, hydrogen (H₂) is considered as a no-carbon fuel; however, safety and storage are the main concerns. Therefore, the H₂ can be potentially utilized with compressed natural gas (CNG) to form hydrogen-enriched compressed natural gas (HCNG) and processed with biofuels to produce hydrogenated biofuels. HCNG emits 20% lower carbon dioxide, 30% less carbon monoxide and 25% reductions in NOx emissions compared with CNG. The hydrogenated biodiesel fuels exhibit higher cetane number and better storage stability. However, the practical challenge is to render them economically affordable with minimum carbon footprints. Thus, the current review is aimed to provide comprehensive detail on the potential of hydrogen in fuel formulation techniques and their effect on engine performance, emission characteristics and various hydrogen production methods viz. blue and green hydrogen. Further, this review highlights the techno-economic characteristics of hydrogen utilization and economic characteristics of the low carbon fuels (both liquid and gaseous fuels) for sustainable mobility.     

Experimental based comparative exergy analysis of a multi-cylinder spark ignition engine fuelled with different gaseous (CNG,HCNG, and hydrogen) fuels

The experimental investigation was carried out on a multi-cylinder spark ignition (SI) engine fuelled with compressed natural gas (CNG), hydrogen blended CNG (HCNG) and hydrogen with varying load at 1500 rpm in order to perform comparative exergy analysis. The exergy analysis indicates that work exergy, heat transfer exergy and exhaust exergy were the highest with hydrogen at all loads due to its high flame temperature, low quenching distance, and high flame speed. The engine's exergy efficiency was the highest with hydrogen (34.23%), and it was about 24.23% and 24.08% with CNG and HCNG respectively at high load (20.25 kW). This indicates a higher potential of hydrogen to convert chemical energy input of fuel into heat and then power output. The exergy destruction was observed minimum with hydrogen at all loads, and it was drastically reduced at high loads. The combustion irreversibility which was calculated using species present during combustion, was the main contributor to exergy destruction, and it decreased with hydrogen. The minimum combustion irreversibility was 11.75% with hydrogen, followed by HCNG and CNG with 16.46% and 18.88% respectively at high load. The high quality of heat due to high in-cylinder temperature and low entropy generation during combustion caused by less number of chemical species in hydrogen combustion are the main reasons for lower combustion irreversibility with hydrogen.     

Effects of compression ratio on performance and emission characteristics of heavy-duty SI engine fuelled with HCNG

The wide range of hydrogen's flammable limits enables ultra-lean combustion. A lean burn reduces the combustion temperature, increases thermal efficiency, and reduces knock, which is a serious problem in a spark ignition (SI) engine. The anti-knock improvement from hydrogen addition makes it feasible to increase the compression ratio (CR) and further improve the thermal efficiency. Herein, the effects of the CR on performance and emission characteristics were investigated using an 11-L heavy-duty SI engine fuelled with HCNG30 (CNG 70 vol%, hydrogen 30 vol%) and CNG. These fuels were used to operate an engine with CRs of 10.5 and 11.5. The results showed that thermal efficiency improved with an increased CR, which significantly decreased CO₂ emission. On the other hand, the NO_x emission was largely increased. Nevertheless, for HCNG30, a CR of 11.5 improved thermal efficiency by 6.5% and decreased NO_x emission by over 75%, as compared to a conventional CNG engine.     

Comparative evaluation of performance,emission, lubricant and deposit characteristics of spark ignition engine fueled with CNG and 18% hydrogen-CNG

Gaseous fuels such as CNG and hydrogen are promising alternative fuels which receive more attention all over the world. This paper investigates the effect of compressed natural gas (CNG) and 18% hydrogen blended compressed natural gas (HCNG) on a retrofitted gasoline genset engine’s performance, emissions, deposits and lubricants under long duration testing. During the 60 h test, lower BSFC, CO and HC are observed for HCNG with the penalty of NOx values. The deposits of iron on spark plug and cylinder liner are higher for HCNG compared to CNG. As kinematic viscosity and TBN values of lubricant decreased significantly with HCNG, it has resulted in higher concentration of wear metals (iron and copper) in the used oil.     

The influences of hydrogen on the performance and emission characteristics of a heavy duty natural gas engine

Because blending hydrogen with natural gas can allow the mixture to burn leaner, reducing the emission of nitrogen oxide (NO_x), hydrogen blended with natural gas (HCNG) is a viable alternative to pure fossil fuels because of the effective reduction in total pollutant emissions and the increased engine efficiency.In this research, the performance and emission characteristics of an 11-L heavy duty lean burn engine using HCNG were examined, and an optimization strategy for the control of excess air ratio and of spark advance timing was assessed, in consideration of combustion stability. The thermal efficiency increased with the hydrogen addition, allowing stable combustion under leaner operating conditions. The efficiency of NO_x reduction is closely related to the excess air ratio of the mixture and to the spark advance timing. With the optimization of excess air ratio and spark advance timing, HCNG can effectively reduce NO_x as much as 80%.     

车用发动机燃用天然气掺氢燃料的性能计算分析与研究

为了研究天然气掺氢发动机的燃烧特性,从模拟试验的角度运用大型发动机软件建立了6缸火花点火天然气掺氢发动机的虚拟样机,并经过试验验证该模型基本准确.通过仿真计算得出,天然气发动机在掺入氢气之后,提高了燃烧速度,明显拓宽了发动机的稀燃极限.在掺入氢气30 %(体积百分比)时,发动机的综合性能指标较好;提高压缩比,指示热效率得到提高.     

The effect of hydrogen on the performance and emissions of an SI engine having a high compression ratio fuelled by compressed natural gas

The aim of this paper is investigation of the effect of hydrogen on engine performance and emissions characteristics of an SI engine, having a high compression ratio, fuelled by HCNG (hydrogen enriched compressed natural gas) blend. The experiments were carried out at 1500, 2000 and 2500 rpm under full load conditions of a modified Isuzu 3.9 L engine, having a compression ratio of 12.5. The engine brake power, brake thermal efficiency, combustion analysis and emissions parameters were realized at 5, 10 15 and 20 deg. CA BTDC (crank angle before top dead center) ignition timings and in excess air ratios of 0.9–1.3 fuelled by hydrogen enriched compressed natural gas (100/0, 95/5, 90/10 and 80/20 of % natural gas/hydrogen).The experimental results showed that the maximum power values were generally obtained with HCNG5 (5% hydrogen in natural gas) fuel. The optimum ignition timing that was obtained according to the maximum brake torque was retarded by the addition of hydrogen to CNG (compressed natural gas), while it was advanced by increasing the engine speed. Furthermore, it was observed that the BTE (brake thermal efficiency) generally declined with the hydrogen addition to compressed natural gas and increasing the engine speed. Additionally, the curves of cylinder pressure and ROHR (rate of heat release values) generally closed to top dead center with the increasing of the hydrogen fraction in the blend and a decreasing engine speed. The hydrocarbon and carbon monoxide emissions generally obtained were lower than the Euro-5 and Euro-6 standards.     

Effect of mixer type on cylinder-to-cylinder variation and performance in hydrogen-natural gas blend fuel engine

Compressed natural gas (CNG) buses were adopted in urban areas as a promising alternative to diesel buses, which emitted plenty of harmful emissions. Although CNG can meet the current emission standards, satisfying the requirements of the next EURO-VI emission regulation without an additional peripheral device may be impossible. The use of a hydrogen-compressed natural gas (HCNG) blend can help achieve a reduction in automotive exhaust emissions as well as prepare for an upcoming hydrogen economy through the construction of hydrogen infrastructure. Moreover, an HCNG engine has higher thermal efficiency than a CNG engine, producing lesser harmful emissions.     

Experimental study on combustion stability and performance of hydrogen-enriched compressed natural gas of a free-piston linear generator

Free Piston linear Generator (FPLG) engine fueled by compressed natural gas (CNG) has recently gained increased research attention. However, due to the low-velocity burning and poor lean limit of CNG fuel, the FPLG engine combustion stability, performance, and efficiency are still low. Hydrogen has a greater burning velocity with wider flame limits that could extend the lean burn limits and combustion characteristics of CNG. This paper compares pure CNG and 10% hydrogen-enriched CNG at various ignition speeds (0.6 ms, 0.8 m/s, and 1 m/s), injection positions (0 mm, 5 mm, 10 mm and 15 mm), and lambda ratios (0.9, 1.4 and 1.7) on the combustion characteristics, performance, and conversion efficiency are duly discussed. The findings show that the FPLG combustion stability limits increase with the hydrogen addition into the CNG. The CNG in-cylinder pressure increases significantly when the injection position is advanced, whereas the hydrogen addition reduces the influence of the injection position. The heat release rate increases by 15.62% and 23.72% with hydrogen addition, corresponding to the advanced and retarded injection positions. Consequently, the hydrogen addition increases the power RMS to 209.21 W and 232.64 W with an increment of 3.46% and 3.13%, respectively. Conclusively, the hydrogen addition into the CNG evidently shortens the combustion duration while improving the heat release rate, combustion stability, power RMS, Cycle-to-Cycle variation, and conversion efficiency.     

Engine characteristics of emissions and performance using mixtures of natural gas and hydrogen

An evaluation was performed on the efficiency and emissions from an engine fuelled with compressed natural gas (CNG) and a mixture of natural gas and hydrogen, respectively. The mixtures of CNG and hydrogen were named HCNG.     

Characterization of HCNG combustion and emission characteristics in a constant volume chamber with a single and a dual spark plug configuration

In an effort to reduce the dependency on crude oil based fuels and to decrease pollutant emissions, hydrogen-CNG (HCNG) attracted a considerable attention with its low HC/CO₂ emission and fast burn rate. In this study, a constant volume chamber with a single spark plug and a dual spark plug configuration was designed to obtain fundamental combustion characteristics of HCNG and to evaluate possible advantages of the dual spark plug over the single spark plug ignition setup. Various mixtures of hydrogen and CNG were systematically experimented to evaluate effects of hydrogen fraction to lean burn limit, combustion pressure, rate of heat release and emission characteristics for both configurations. With the current experimental results, it was clearly demonstrated that an appropriate mixture of HCNG along with a suitable spark plug configuration, could become a promising candidate to replace the crude oil based IC engine fuels to alleviate the dependency on the depleting petroleum resource and to meet the stricter emission regulation.     

Effect of natural gas enrichment with hydrogen on combustion process and emission characteristic of a dual fuel diesel engine

The paper presents results of experimental research on a dual-fuel engine powered by diesel fuel and natural gas enriched with hydrogen. The authors attempted to replace CNG with hydrogen fuel as much as possible with a constant dose of diesel fuel of 10% of energy fraction. The tests were carried out for constant engine load of IMEP = 0.7 MPa and a rotational speed of n = 1500 rpm. The effect of hydrogen on combustion, heat release, combustion stability and exhaust emissions was analyzed. In the test engine, the limit of hydrogen energy fraction was 19%. The increase in the fraction caused an increase in the cycle-by-cycle variation and the occurrence of engine knocking. It was shown that the enrichment of CNG with hydrogen allows for the improvement in the combustion process compared to the co-combustion of diesel fuel with non-enriched CNG, where the reduction in the duration of combustion by 30% and shortening the time of achieving 50% of MFB by 50% were obtained. The evaluation of the spread of the end of combustion is also presented. For H₂ energetic share over 20%, the spread of end of combustion was 48° of crank angle. Measurement of exhaust emissions during the tests revealed an increase in THC and NO_x emissions.     

A fractal-based quasi-dimensional combustion model for SI engines fuelled by hydrogen enriched compressed natural gas

A quasi-dimensional model based on the concepts of fractal geometry has been developed for an SI engine fuelled with natural gas/hydrogen blends. The fundamentals of the thermodynamic model, the fractal combustion model and related equations are introduced. This paper investigates the influence of manifold absolute pressure, equivalence ratio and hydrogen fraction on fractal dimension and improves the fractal dimension expression. Comparisons are conducted between the improved and original models by the prediction outcomes. After the determination of model constants by calibration, the model predictions of cylinder pressure histories and mass fraction burned of an HCNG engine are then compared with experimental data over a wide range of loads, equivalence ratios, engine speeds and hydrogen blending ratios. The pressure profiles show that predictions of the improved model match quite well with the experimental results except for the early combustion stage. The improved model is proved to be more suitable for predicting HCNG engine performance.     

Twenty percent hydrogen-enriched natural gas transient performance research

In order to increase engine transient performance of 20% hydrogen-enriched natural gas, research including the comparing of ETC cycle emissions in different catalysts, different enrichment rates, and data was taken for both 20% HCNG and pure natural gas. The exhaust composition and efficiency was tested using three different oxidization catalysts: ECOCAT type I, a Domestic catalysts, and ECOCAT typeII. Using these three catalysts, the results show that increasing catalytic efficiency results in increased exhaust resistance, reduced engine power and increased BSFC. All of the three catalytic converters reduce the exhaust emissions, therefore, allowing hydrogen-enriched natural gas engines to more easily achieve Enhanced Environmentally Friendly Vehicle (EEV) standards. By increasing the enrichment rate, the engine's torque increases, which results in increased emissions, especially NOx. According to the data taken using 20% HCNG without a catalytic converter emissions values, compared with no HCNG, for NOx, CO, NMHC, CH₄ were 51%, 36%, 60%, 47% the emissions of pure CNG, respectively, with the BSFC at 7%. But as research shows, by using a catalytic converter, hydrogen-enriched natural gas has the potential to achieve European III standards.