Engine combustion and emission fuelled with natural gas: A review

Natural gas (NG) is one of the most important and successful alternative fuels for vehicles. Engine combustion and emission fuelled with natural gas have been reviewed by NG/gasoline bi-fuel engine, pure NG engine, NG/diesel dual fuel engine and HCNG engine. Compared to using gasoline, bi-fuel engine using NG exhibits higher thermal efficiency; produces lower HC, CO and PM emissions and higher NOx emission. The bi-fuel mode can not fully exert the advantages of NG. Optimization of structure design for engine chamber, injection parameters including injection timing, injection pressure and multi injection, and lean burn provides a technological route to achieve high efficiency, low emissions and balance between HC and NOx. Compared to diesel, NG/diesel dual fuel engine exhibits longer ignition delay; has lower thermal efficiency at low and partial loads and higher at medium and high loads; emits higher HC and CO emissions and lower PM and NOx emissions. The addition of hydrogen can further improve the thermal efficiency and decrease the HC, CO and PM emissions of NG engine, while significantly increase the NOx emission. In each mode, methane is the major composition of THC emission and it has great warming potential. Methane emission can be decreased by hydrogen addition and after-treatment technology.     

Stoichiometric H2ICEs with water injection

For the most part, gasoline engines operate close to stoichiometry because of the high power density and the easy after treatment through the very well established three-way catalytic converter technology. The lean burn gasoline engine suffers major disadvantages for the after treatment still requiring aggressive research and development to meet future emission standards more than for the lower power density compensated by the better fuel conversion efficiency running lean. Hydrogen engines are usually run ultra-lean to avoid abnormal combustion phenomena and possibly to avoid the emission of nitrogen oxides without the difficult non-stoichiometric after treatment. While the ultra-lean combustion of hydrogen may reduce the formation of NOx within the cylinder but makes the power density very low, the only lean combustion of hydrogen requires after treatment for NOx reduction. The suppression of abnormal combustion in hydrogen engines has been a challenge for the three regimes of abnormal combustion, knock (auto ignition of the end gas region), pre-ignition (uncontrolled ignition induced by a hot spot prior of the spark ignition) and backfire (premature ignition during the intake stroke, which could be seen as an early form of pre-ignition). Direct injection and jet ignition coupled to port water injection are used here to avoid the occurrence of all these abnormal combustion phenomena as well as to control the temperature of gases to turbine in a turbocharged stoichiometric hydrogen engine.     

Investigation of hydrogen addition to methanol-gasoline blends in an SI engine

In this study, effects of hydrogen-addition on the performance and emission characteristics of Methanol-Gasoline blends in a spark ignition (SI) engine were investigated. Experiments were conducted with a four-cylinder and four stroke spark ignition engine. Performance tests were performed via measuring brake thermal efficiency, brake specific fuel consumption, cylinder pressure and exhaust emissions (CO, CO₂, HC, NOx). These performance metrics were analyzed under three engine load conditions (no load, 50% and 100%) with a constant speed of 2000 rpm. Methanol was added to the gasoline up to 15% by volume (5%, 10% and 15%). Besides, hydrogen was added to methanol-gasoline mixtures up to 15% by volume (3%, 6%, 9% and 15%). Results of this study showed that methanol addition increases BSFC by 26% and decreases thermal efficiency by 10.5% compared to the gasoline. By adding hydrogen to the methanol - gasoline mixtures, the BSFC decreased by 4% and the thermal efficiency increased by 2% compared to the gasoline. Hydrogen addition to methanol – gasoline mixtures reduces exhaust emissions by about 16%, 75% and 15% of the mean average values of HC, CO and CO2 emissions, respectively. Lastly, ?t was concluded that hydrogen addition improves combustion process; CO and HC emissions reduce as a result of the leaning effect caused by the methanol addition; and CO2 and NOx emission increases because of the improved combustion.     

Possibilities of improving the performance of a spark ignition engine working with hydrogen as supplementary fuel

The usage of hydrogen as supplementary fuel to the gasoline-air mixture for spark ignition engines results in considerable improvement of the engine efficiency and in the reduction of the toxic components in the exhaust gases in comparison with the conventional spark ignition gasoline engine. However, when leaning the fuel-air mixture for certain conditions, an increase of the emission of nitric oxides in the exhaust gases is observed. The indices of the engine have been studied at various ratios of hydrogen and gasoline in the mixture. The possibility of the engine power quality adjustment has also been studied.     

Hydrogen fueled spark ignition engine with electronically controlled manifold injection: An experimental study

In this work, a single cylinder conventional spark ignition engine was converted to operate with hydrogen using the timed manifold fuel injection technique. A solenoid operated gas injector was used to inject hydrogen into the inlet manifold at the specified time. A dedicated electronic circuit developed for this work was used to control the injection timing and duration. The spark timing was set to minimum advance for best torque (MBT). The engine was operated at the wide-open throttle condition. For comparison of results, the same engine was also run on gasoline.The performance and emission characteristics with hydrogen and gasoline are compared. From the results, it is found that there is a reduction of about 20% in the peak power output of the engine when operating with hydrogen. The brake thermal efficiency with hydrogen is about 2% greater than that of gasoline. A lean limit equivalence ratio of about 0.3 could be attained with hydrogen as compared to 0.83 with gasoline. CO, CO₂ and HC emissions were negligible with hydrogen operation. However, for hydrogen operation, NO_x emission was four times higher than that of gasoline at full load power. The best ignition timing for hydrogen was much retarded when compared to gasoline. The effect of hydrogen injection pressure was also studied and no specific changes were observed. The effect of operating speed was also studied.     

Experimental and numerical investigation of effects of CNG and gasoline fuels on engine performance and emissions in a dual sequential spark ignition engine

Compared to widening usage of CNG in commercial gasoline engines, insufficient but increasing number of studies have appeared in open literature during last decades while engine characteristics need to be quantified in exact numbers for each specific fuel converted engine. In this study, a dual sequential spark ignition engine (Honda L13A4 i-DSI) is tested separately either with gasoline or CNG at wide open throttle. This specific engine has unique features of dual sequential ignition with variable timing, asymmetrical combustion chamber, and diagonally positioned dual spark-plug. Thus, the engine led some important engine technologies of VTEC and VVT. Tests are performed by varying the engine speed from 1500 rpm to 4000 rpm with an increment of 500 rpm. The engine’s maximum torque speed of 2800 rpm is also tested. For gasoline and CNG fuels, engine performance (brake torque, brake power, brake specific fuel consumption, brake mean effective pressure), emissions (O₂, CO₂, CO, HC, NO_x, and lambda), and the exhaust gas temperature are evaluated. In addition, numerical engine analyses are performed by constructing a 1-D model for the entire test rig and the engine by using Ricardo-Wave software. In the 1-D engine model, same test parameters are analyzed, and same test outputs are calculated. Thus, the test and the 1-D engine model are employed to quantify the effects of gasoline and CNG fuels on the engine performance and emissions for a unique engine. In general, all test and model results show similar and close trends. Results for the tested commercial engine show that CNG operation decreases the brake torque (12.7%), the brake power (12.4%), the brake mean effective pressure (12.8%), the brake specific fuel consumption (16.5%), the CO₂ emission (12.1%), the CO emission (89.7%). The HC emission for CNG is much lower than gasoline. The O₂ emission for CNG is approximately 55.4% higher than gasoline. The NO_x emission for CNG at high speeds is higher than gasoline. The variation percentages are the averages of the considered speed range from 1500 rpm to 4000 rpm.     

Effect of addition of hydrogen and TiO2 in gasoline engine in various exhaust gas recirculation ratio

The effects of hydrogen ratios on combustion and emission characteristics of gasoline engine were studied under different exhaust gas recirculation (EGR), ignition timing and ignition pressure. The test performed in a modified gasoline direct ignition engine at different hydrogen ratios of 0%, 5%, 10% and 25%. In addition, the EGR rate set to 0%, 5%, 10% and 20% to study the combustion and emission characteristics. Addition to the different hydrogen fractions, 5% of TiO₂ is added to increase the combustion characteristics with reduced emission. Regarding the results of the current study, the engine torque increases by 15% due to the addition of hydrogen in gasoline, while mechanical efficiency is improved by achieving a large throttle opening. At the same time, NOx emission decreased by 62% compared to the unmodified engine due to the influence of EGR, hydrogen ratio and high oxygen concentration TiO₂. Moreover, the emission of CO and HC also reduced due to the influence of hydrogen fuel. Additionally, few more tests are taken to monitor the effect of the injection pressure for the hydrogen fuel. Higher injection reports higher effective thermal efficiency at 4 MPa and lower NOx. Reasonable injection pressure results in shorten flame development period.     

Investigation of hydrogen usage on combustion characteristics and emissions of a spark ignition engine

In this study, initially, a single cylinder, naturally aspirated, spark ignition engine was loaded with AC engine dynamometer and a spark plug type engine transducer was used to obtain in-cylinder pressure. The test engine was operated with gasoline fuel at full load and different engine speeds (3100, 3200, 3300, 3400 and 3450 rpm). Secondly, using obtained engine performance, emission values and in-cylinder pressure, a one dimensional engine model was built and validated by an engine performance and emission analysis software (AVL-Boost). After the validation of single dimensional theoretical engine model, a comparison was made between the emission, performance and combustion (in-cylinder pressure, rate of heat release) values of operations with pure hydrogen fuel and such values of the operations with unleaded gasoline. The emissions of CO and total hydrocarbons (THC) were negligible with using hydrogen as fuel in SI engine. A dramatic increase in NO_x emissions was obtained with using hydrogen as fuel. However, by using hydrogen in lean conditions, NO_x emissions were taken under control by means of wide flammability limits of hydrogen.     

Effects of ignition advance on a dual sequential ignition engine at lean mixture for hydrogen enriched butane usage

In this study, the effects of ignition advance on dual sequential ignition engine characteristics and exhaust gas emissions for hydrogen enriched butane usage and lean mixture were investigated numerically and experimentally. The main purpose of this study is to reveal the effects of h-butane application in a commercial spark ignition gasoline engine. One cylinder of the commercially dual sequential spark ignition engine was modeled in the Star-CD software, taking into account all the components of the combustion chamber (intake-exhaust manifold connections, intake-exhaust valves, cylinder, cylinder head, piston, spark plugs). Angelberger wall approximation, k-ε RNG turbulence model and G-equation combustion model were used for analysis. In the dual sequential spark ignition, the difference between the spark plugs was defined as 5° CAD. At the numerical analysis; 10.8:1 compression ratio, 1.3 air-fuel ratio, 2800 rpm engine speed, 0.0010 m the flame radius and 0.0001 m the flame thickness were kept constant. The hydrogen-butane mixture was defined as 4%–96% by mass. In the analysis, the optimal ignition advance was determined by the working conditions. In addition, the effects of changes in ignition advance were examined in detail at lean mixture. For engine operating conditions under investigation, it has been determined that the 50° CAD ignition advance from the top dead center is the optimal ignition advance in terms of engine performance and emission balance. It has also been found that the NO_x formation rises up as the ignition advance increases. The BTE values were approximately 12.01% higher than butane experimental results. The experimental BTE values for h-butane were overall 3.01% lower than h-butane numerical results.     

增压稀燃天然气掺氢发动机排放特性

为了研究20%掺氢比的增压稀燃天然气掺氢(HCNG)发动机的排放特性,通过对发动机进行了空燃比和点火提前角调整试验、ETC循环测试试验和加装氧化型催化器试验,获得了20%HCNG发动机的排放规律.CH4排放随着空燃比的增大先减少后增加;CO排放在高于理论空燃比后骤减;Nox排放随着空燃比的增大先增加后减少,在空燃比19～21 左右达到最大值,1600～1800r/min时最低.CO、Nox随着点火提前角的增大而增加;CH4随着点火提前角的增大略有增加,并且点火提前角越大,对CH4排放的影响越小.加装催化器后,CO、CH4的转化效率均＞90%.试验结果表明:增压稀燃和氧化型催化器相结合是天然气掺氢发动机节能减排的有效方案.     

Experimental investigation of SI engine characteristics using Acetone-Butanol-Ethanol (ABE) – Gasoline blends and optimization using Particle Swarm Optimization

This study conducts an experimental investigation of spark ignition (SI) engine characteristics using gasoline blended with Acetone-Butanol-Ethanol (ABE) that act as hydrogen and oxygen carriers. The number of experiments is planned and executed according to a design of experiments with full-factorial design, wherein ABE blend percentage and speed are taken as input parameters and brake thermal efficiency (BTE), emissions of carbon monoxide (CO), hydrocarbon (HC), and oxides of nitrogen (NOx) are taken as the responses. In the present study, a multi-objective optimization technique, Particle Swarm Optimization (PSO), is used to optimize spark ignition engine performance and emission parameters. The results predicted by the regression model are compared with the experimental results. PSO is used to study the Pareto front of BTE, CO, HC, and NOx, respectively. The results indicated that when the engine is run at 1500 rpm, with the fuel blend having 5.4% ethanol, a minimum value of 0.58% CO, 211 ppm of HC are obtained, giving a maximum BTE of 28%. Similarly, when the engine is run at 2264 rpm with a 5% ethanol blend, minimum NOx emission of 1029 ppm and a maximum BTE of 30% are obtained.     

Future fuels and mixture preparation methods for spark ignition automobile engines

Research in the automobile industry focuses on studies of spark ignition automobile engines especially of stratified charge engines, lean combustion concepts, engines fueled by alcohol/gasoline blends, alcohol engines, and engines with on-board gas generators fueled by a variety of liquid fuels. The goal of this work is the development of low-emission, high fuel-economy and high performance power systems for the early 1990s. The implementation of this objective makes it necessary for more information on future fuel characteristics. In addition proper mixture preparation methods must be applied to find solutions to specific problems such as NO_x formation and aldehyde emission, while maintaining good fuel economy and high engine efficiency. The goal of this paper is to discuss the most attractive approaches for improved preparation and distribution of the fuel-air mixture with respect to future fuels such as alcohol/gasoline blends and other alcohol fuels.     

Effects of hydrogen injection strategy on the hydrogen mixture distribution and combustion of a gasoline/hydrogen SI engine under lean burn condition

Hydrogen is a carbon free energy carrier with high diffusivity and reactivity, it has been proved to be a kind of suitable blending fuel of spark ignition (SI) engine to achieve better efficiency and emissions. Hydrogen injection strategy affects the engine performance obviously. To optimize the combustion and emissions, a comparative study on the effects of the hydrogen injection strategy on the hydrogen mixture distribution, combustion and emission was investigated at a SI engine with gasoline intake port injection and four hydrogen injection strategies, hydrogen direct injection (HDI) with stratified hydrogen mixture distribution (SHMD), hydrogen intake port injection with premixed hydrogen mixture distribution (PHMD), split hydrogen direct injection (SHDI) with partially premixed hydrogen mixture distribution (PPHMD) and no hydrogen addition. Results showed that different hydrogen injection strategy formed different kinds of hydrogen mixture distribution (HMD). The ignition and combustion rate played an important role on engine efficiency. Since the SHDI could use two hydrogen injection to organize the HMD, the ignition and combustion rate with the PPHMD was the fastest. With the PPHMD, the brake thermal efficiency of the engine was the highest and the emissions were slight more than that with the PHMD. PHMD achieve the optimum emission performance by its homogeneous hydrogen. The engine combustion and emission performance can be optimized by adjusting the hydrogen injection strategy.     

A Taguchi-fuzzy based multi-objective optimization study on the soot-NOx-BTHE characteristics of an existing CI engine under dual fuel operation with hydrogen

The present energy situation and the concerns about global warming has stirred active research interest in non-conventional and alternative fuel resources to reduce the emission and the unabated fossil fuel dependency footprint, particularly for transportation, power generation and agricultural sectors. Among various alternatives, hydrogen has been extensively studied and concluded to be a viable and promising alternative fuel option on existing IC engine platforms in bridging the contemporary gap to the long term fuel cell based power train roadmap. Further, with the advent of EPA Tier 4 interim and final emission mandates the limits of the regulated emissions are challenging the practical limits of current engine design and calibration strategies. With a compliance directive of a substantial reduction in Soot and NOx emission levels simultaneously than its immediately preceding directives, engine manufacturers are being increasingly challenged to meet the paradox of curtailing particulate matter and NOx emissions on one hand and maintaining consumer expectations of increased thermal efficiency on the other. In this respect, various studies on the application of hydrogen as a dual fuel in existing IC engines offer the motivation to explore the potential in exploiting the inherent superior combustion characteristics of hydrogen as an in situ solution to the emission and performance trade-off challenges of conventional diesel combustion. In the present study, an experimental investigation was carried out existing CI engine with hydrogen as a dual fuel. A Timed Manifold Injection (TMI) system was adopted to analyze the effect of durations of hydrogen induced on the performance and emission characteristics as compared to baseline diesel operation. Previous studies have already clearly established the virtues of hydrogen in mitigating the emission footprint of conventional diesel operation along with improved performance characteristics. However, with the penalty of increased NOx emissions with hydrogen participation, a definite study specifically addressing the NOx-Soot-BTHE trade-off vantage achievable on existing CI engines under the purview of existing emission mandates is yet to be addressed. Based on an experimental investigation, the present study employs offline calibration techniques centered on the rationale of the fuzzy logic based Taguchi analysis to investigate the optimal soot-NOx-BTHE trade-off regime of operation based on different hydrogen injection strategies.     

丙酮-丁醇-乙醇(ABE)/汽油混合燃料对高速发动机性能影响的试验研究

以发动机4000r/min、节气门开度35%为试验工况,对纯汽油及不同掺混体积分数丙酮-丁醇-乙醇(acetone-butanol-ethanol,ABE)与汽油混合物开展了不同点火提前角和喷油量的试验研究。分析了不同ABE混合比、点火提前角和过量空气系数对发动机性能的影响,并对每种燃料发动机最大功率工况的性能参数进行了比较。结果表明：点火提前角和过量空气系数相同时,混合燃料中ABE含量越高,燃油流量越大,发动机功率越大,有效热效率越高;燃油流量的总热量增大和热-功转换效率提高是促使发动机功率增大的主要原因;随ABE掺混比增加,NO比排放明显降低,CO比排放略有增加,碳氢化合物比排放先增后减。浓混合气工况增加ABE含量比在当量空燃比状态下增加ABE含量,发动机的有效热效率增大更明显,发动机的NO比排放降低更加明显。研究表明高速汽油机掺混ABE燃料具有较好的应用前景。     

电喷汽油机燃用醇汽油混合燃料的试验研究

研究了多点电喷汽油机燃用醇汽油混合燃料的性能。研究结果表明:在汽油机参数未做任何调整的情况下,醇汽油混合燃料发动机的动力性与汽油机相比有所降低,燃料经济性改善,有效热效率提高。随醇类燃料体积分数的增大,CO排放明显改善,THC排放略有升高,NOx排放的变化不明显。醇汽油混合燃料发动机的醛类排放物明显升高,汽油机的未燃甲醇排放较高,未燃乙醇排放变化不明显。     

Performance,combustion and emission characteristics of a spark‐ignition engine with simultaneous injection of n‐butanol and gasoline in comparison to blended butanol and gasoline

Simultaneous injection of n‐butanol and gasoline through a new system of two injectors directing the sprays towards the back of the intake valve in a spark‐ignition engine was tried in lieu of injecting a blend of these fuels through a single injector. This system avoids the problem of phase separation, which is generally faced during the use of alcohol‐gasoline blends. Experiments were conducted on a spark‐ignition engine with this dual injection system using a fuel ratio of 1:1 (B50S) on the mass basis. High‐speed photographs indicated that the sprays from the injectors did not interfere till they reached the intake valve. Comparisons were made with pre‐blended butanol‐gasoline (B50) and neat (100%) gasoline at the best spark timing. All injection and spark parameters were controlled using a real time engine controller. Neat n‐butanol (B100) was superior only near full throttle with improved efficiency of the engine of about 1.2% (absolute). Heat release rates were observed to be higher and more advanced with B100 at wide open throttle. However, a reverse of this trend was observed at the throttle position of 15%. NO emission was also lower by 30% with B100 at wide open throttle as compared with gasoline. However, a small increase in carbon monoxide (CO) levels was observed because of lower post combustion temperatures as compared with gasoline and B50S. Simultaneous injection reduced hydrocarbon (HC) emissions by 13% to 50% as compared with B50 (blended fuel). HC emissions with gasoline and B50S were similar. Nitric oxide (NO) emission was lower with B50S as compared with gasoline; however it was higher than B50 because of better combustion. On the whole, the developed dual injection system was superior to the conventional method of blending in terms of performance, emissions and ability to change the fuel ratio as needed. B50S is suitable at all throttle positions, whereas B100 shows benefits at full throttle conditions. Copyright © 2013 John Wiley & Sons, Ltd.     

Hydrogen–ethanol blending as an alternative fuel of spark ignition engines

The performance and pollutant emission of a four-stroke spark ignition engine using hydrogen–ethanol blends as fuel have been studied. The tests were performed using 2, 4, 6, 8, 10 and 12 mass% hydrogen–ethanol blends. Gasoline fuel was used as a basis for comparison. The effect of using different blends of hydrogen–ethanol on engine power, specific fuel consumption, CO and NO_x emission was studied. Operating test results for a range of compression ratio (CR) and equivalent ratio are presented. The results show that the supplemental hydrogen in the ethanol–air mixture improves the combustion process and hence improves the combustion efficiency, expands the range of combustibility of the ethanol fuel, increases the power, reduces the s.f.c., and reduces toxic emissions. The important improvement of hydrogen addition is to reduce the s.f.c. of ethanol engines. Results were compared to those with gasoline fuel at 7 CR and stoichiometric equivalence ratio.     

Experimental study of combustion performances and emissions of a spark ignition cogeneration engine operating in lean conditions using different fuels

This work presents an experimental study describing a six-cylinder spark ignition engine running with a lean equivalence ratio, high compression ratio, ignition delay and used in a cogeneration system (heat and electricity production). Three types of fuels; natural gas, pure methane and methane/hydrogen blend (85% CH₄ and 15% H₂ by volume), were used for comparison purposes. Each fuel has been investigated at 1500 rpm and for various engine loads fixed by electrical power output conditions. CO, CO₂, HC, and NOx emissions values, and exhaust gas temperature were measured. The effect of fuel composition on engine characteristics has been studied. The results show, that the hydrogen addition increased HC emissions (around 18%), as well as performance, whilst it reduced NO_x (around 31%), exhaust gas temperature, CO and CO₂.