Knock rating of gaseous fuels in a single cylinder spark ignition engine

This paper presents the determination of knock rating of gaseous fuels in a single cylinder engine. The first part of the work deals with an application of a standard method for the knock rating of gaseous fuels. The Service Methane Number (SMN) is compared with the standard Methane Number (MN) calculated from the standard AVL software METHANE (which corresponds to the MN measured on a Cooperative Fuel Research engine). Then, in the second part, the ‘mechanical’ resistance to knock of our engine is highlighted by means of the Methane Number Requirement (MNR). A single cylinder LISTER PETTER engine was modified to run as a spark ignition engine with a fixed compression ratio and an adjustable spark advance. Effects of engine settings on the MNR are deduced from experimental data and compared extensively with previous studies. Using the above, it is then possible to adapt the engine settings for optimal knock control and performances. The error on the SMN and MNR stands beneath ±2 MN units over the gases and engine settings considered.     

Methane number testing of alternative gaseous fuels

Alternative gaseous fuels, like syn-gas and bio-gas, are attractive fuels for internal combustion engines due to energy and environmental concerns. Although the worldwide use of alternative gaseous fuels has increased, the knock properties of these fuels are not well understood. The methane number (MN) knock rating technique was selected based on its range and sensitivity. Eight alternative gaseous fuel compositions were simulated with a gas blending system and tested for MN in a Cooperative Fuel Research (CFR) F-2 engine. The alternative gaseous fuels ranged from 24 to 140 MN (natural gas typical range 75-95).     

Safe operating conditions determination for stationary SI gas engines

Knock is a major problem when running combined heat and power (CHP) gas engines because of the variation in the network natural gas composition. A curative solution is widely applied, using an accelerometer to detect knock when it occurs. The engine load is then reduced until knock disappears. The present paper deals with a knock preventive device. It is based on the knock prediction following the engine operating conditions and the fuel gas methane number, and it acts on the engine load before knock happens. A state of the art about knock prediction models is carried out. The maximum of the knock criterion is selected as knock risk estimator, and a limit value above which knock may occur is defined. The estimator is calculated using a two-zone thermodynamic model. This model is specifically based on existing formulas for the calculation of the combustion progress, modified to integrate the effect of the methane number. A chemical kinetic model with 53 species and 325 equilibrium reactions is used to calculate unburned and burned gases composition. The different parameters of the model are fitted with a least squares method from an experimental data base. Errors less than 8% are achieved. The knock risks predicted for various natural gases and operating conditions are in agreement with previous work. Nevertheless, the knock risk estimator is overestimated for natural gases with high concentrations of inert gases such as nitrogen and carbon dioxide. The definition of a methane number limit based on the engine manufacturer's recommendation is then required to eliminate unwarranted alerts. Safe operating conditions are thus calculated and gathered in the form of a map. This map, combined with the real time measurement of the fuel gas methane number, can be integrated to the control device of the CHP engine in order to guarantee a safe running towards fuel gas quality variation.     

Combustion of n-butanol in a spark-ignition IC engine

Alcohols, because of their potential to be produced from renewable sources and because of their high quality characteristics for spark-ignition (SI) engines, are considered quality fuels which can be blended with fossil-based gasoline for use in internal combustion engines. They enable the transformation of our energy basis in transportation to reduce dependence on fossil fuels as an energy source for vehicles. The research presented in this work is focused on applying n-butanol as a blending agent additive to gasoline to reduce the fossil part in the fuel mixture and in this way to reduce life cycle CO₂ emissions. The impact on combustion processes in a spark-ignited internal combustion engine is also detailed. Blends of n-butanol to gasoline with ratios of 0%, 20%, and 60% in addition to near n-butanol have been studied in a single cylinder cooperative fuels research engine (CFR) SI engine with variable compression ratio manufactured by Waukesha Engine Company. The engine is modified to provide air control and port fuel injection. Engine control and monitoring was performed using a target-based rapid-prototyping system with electronic sensors and actuators installed on the engine [1]. A real-time combustion analysis system was applied for data acquisition and online analysis of combustion quantities. Tests were performed under stoichiometric air-to-fuel ratios, fixed engine torque, and compression ratios of 8:1 and 10:1 with spark timing sweeps from 18° to 4° before top dead center (BTDC). On the basis of the experimental data, combustion characteristics for these fuels have been determined as follows: mass fraction burned (MFB) profile, rate of MFB, combustion duration and location of 50% MFB. Analysis of these data gives conclusions about combustion phasing for optimal spark timing for maximum break torque (MBT) and normalized rate for heat release. Additionally, susceptibility of 20% and 60% butanol-gasoline blends on combustion knock was investigated. Simultaneously, comparison between these fuels and pure gasoline in the above areas was investigated. Finally, on the basis of these conclusions, characteristic of these fuel blends as substitutes of gasoline for a series production engine were discussed.     

Stratification of fuel for better engine performance

The concept of fuel stratification has been proposed and applied to a four-valve port injection spark ignition engine. In this engine, two different fuels or fuel components are admitted through two separate inlet ports and stratified into two regions laterally by strong tumble flows. Each stratified region has a spark plug to control the ignition. This engine can operate in the stratified lean-burn mode at part loads when fuel is supplied only to one of the inlet ports. While at high load operation, an improved fuel economy and higher power output are also expected through increased anti-knock features by taking advantage of the superior characteristics of different fuel or fuel components. This is achieved by igniting the lower RON (research octane number) fuel first and leaving the higher RON fuel in the end gas region. In this paper, knock limits of homogenous and different fuel stratification combustion modes at high loads were investigated experimentally. Primary reference fuels (PRF), iso-octane and n-heptane, were used to simulate three fuels of different RON: RON90, RON95 and RON100. The research results show that with stratified fuel components of low and high octane numbers, the knock limit, as defined by the minimum spark advance for knocking combustion, was extended apparently when the lower RON fuel was ignited first. In addition, the knock limit could also be extended by increasing the amount of higher RON fuel. However, igniting first the lower RON fuel in the fuel stratification combustion mode produced little improvement in anti-knock behaviour over the homogeneous combustion of the mixture of those two stratified fuels with an average RON.     

Kinetic and CFD Modeling of Exhaust Gas Reforming of Natural Gas in a Catalytic Fixed-Bed Reactor for Spark Ignition Engines

Fuel reforming is an attractive method for performance enhancement of internal combustion engines fueled by natural gas, since the syngas can be generated inline from the reforming process. In this study, 1D and 2D steady-state modeling of exhaust gas reforming of natural gas in a catalytic fixed-bed reactor were conducted under different conditions. With increasing engine speed, methane conversion and hydrogen production increased. Similarly, increasing the fraction of recirculated exhaust gas resulted in higher consumption of methane and generation of H₂ and CO. Steam addition enhanced methane conversion. However, when the amount of steam exceeded that of methane, less hydrogen was produced. Increasing the wall temperature increased the methane conversion and reduced the H₂/CO ratio.     

煤层气发电与机型选择

煤层气作为一种洁净能源进行发电,可根据开采气体的浓度,选择燃气轮机或燃气内燃机,进行热电联产具有很好的效益。     

Combustion performance of bio-ethanol at various blend ratios in a gasoline direct injection engine

Bio-ethanol has the potential to be used as an alternative to petroleum gasoline for the purpose of reducing the total CO₂ emissions from internal combustion engines and this paper is devoted to the investigation of using different blending-ratios of bio-ethanol/gasoline with respect to spark timing and injection strategies. The experimental work has been carried out on a direct injection spark ignition engine at a part load and speed condition. It is shown that the benefits of adding ethanol into gasoline are reduced engine-out emissions and increased efficiency, and the impact changes with the blend ratio following a certain pattern. These benefits are attributed to the fact that the addition of ethanol modifies the evaporation properties of the fuel blend which increases the vapour pressure for low blends and reduces the heavy fractions for high blends. This is furthermore coupled with the presence of oxygen within the ethanol fuel molecule and the contribution of its faster flame speed, leading to enhanced combustion initiation and stability and improved engine efficiency.     

GOV10电子调速器在Cooper天然气发动机上配套技术应用

GOV10是美国ALTRONIC公司针对大型天然气发动机或内燃机设计的一种高科技电子产品,它集成了先进的测量技术、控制技术以及现代信息技术,近几年广泛应用于各种天然气发动机。文章介绍了Cooper天然气发动机在调速控制上存在的问题及GOV10电子调速器在该机组上配套技术应用情况。     

催化燃烧中表面反应-气相反应间相互作用及其对均质压燃发动机着火特性的影响

通过对微元管中甲烷在铂表面的催化燃烧过程的数值计算,分析了当混合气入口压力很高时气相反应对整个催化燃烧过程的影响;通过敏感度分析,找出了对异相着火及气相着火起主要作用的基元反应步.结果表明,在异相着火过程中起主要作用的基元反应步为甲烷与氧气在催化剂表面的吸附反应及氧气的解吸反应,在气相着火过程中起主要作用的基元反应步为OH·及水的吸附与解吸反应.对活塞顶涂有铂催化剂的均质压燃（HCCI）发动机的燃烧过程进行了数值模拟,分析了催化效应及关键表面反应基元步对HCCI发动机着火时刻以及燃烧过程中中间组分的影响,结果表明,催化反应能促进混合气的着火,缩短着火延迟时间,对HCCI发动机着火时刻起主要影响的表面反应为OH·及水的吸附与解吸反应.     

Investigation on combustion and emissions of DME/gasoline mixtures in a spark-ignition engine

Dimethyl ether (DME) has a lot of good properties and is thought to be one of the best alternative fuels for IC engines in the future. In order to improve the efficiency, combustion stability and emissions performance of a spark-ignited (SI) gasoline engine at stoichiometric condition, an experimental study aiming at improving engine performance through DME addition was carried out on a four-cylinder SI engine. The engine was modified to be fueled with the mixture of gasoline and DME which were injected into the engine intake ports simultaneously. A hybrid electronic control unit (HECU) was dedicatedly developed to control the injection timings and durations of gasoline and DME. The spark timing was adjusted to reach the maximum brake torque (MBT) without knocking. Various DME fractions were selected to investigate the effect of DME addition on engine performance, thermal efficiency, combustion characteristics, cyclic variation and emissions under stoichiometric conditions. The experimental results showed that thermal efficiency, NOx and HC emissions are improved with the increase of DME addition level. The combustion performance was improved when DME addition fraction was less than 10%. CO emission first decreased and then increased with the increase of DME enrichment level at stoichiometric condition.     

Investigations on surrogate fuels for high-octane oxygenated gasolines

Gasoline is a complex mixture that possesses a quasi-continuous spectrum of hydrocarbon constituents. Surrogate fuels that decrease the chemical and/or physical complexity of gasoline are used to enhance the understanding of fundamental processes involved in internal combustion engines (ICEs). Computational tools are largely used in ICE development and in performance optimization; however, it is not possible to model full gasoline in kinetic studies because the interactions among the chemical constituents are not fully understood and the kinetics of all gasoline components are not known. Modeling full gasoline with computer simulations is also cost prohibitive. Thus, surrogate mixtures are studied to produce improved models that represent fuel combustion in practical devices such as homogeneous charge compression ignition (HCCI) and spark ignition (SI) engines. Simplified mixtures that represent gasoline performance in commercial engines can be used in investigations on the behavior of fuel components, as well as in fuel development studies. In this study, experimental design was used to investigate surrogate fuels. To this end, SI engine dynamometer tests were conducted, and the performance of a high-octane, oxygenated gasoline was reproduced. This study revealed that mixtures of iso-octane, toluene, n-heptane and ethanol could be used as surrogate fuels for oxygenated gasolines. These mixtures can be used to investigate the effect of individual components on fuel properties and commercial engines performance.     

NOx reduction from a large bore natural gas engine via reformed natural gas prechamber fueling optimization

Lean combustion is a standard approach used to reduce NO_x emissions in large bore (35–56 cm) stationary natural gas engines. However, at lean operating points, combustion instabilities and misfires give rise to high total hydrocarbon (THC) and carbon monoxide (CO) emissions. To counteract this effect, precombustion chamber (PCC) technology is employed to allow engine operation at an overall lean equivalence ratio while mitigating the rise of THC and CO caused by combustion instability and misfires. A PCC is a small chamber, typically 1–2% of the clearance volume. A separate fuel line supplies gaseous fuel to the PCC and a standard spark plug ignites the slightly rich mixture (equivalence ratio 1.1–1.2) in the PCC. The ignited PCC mixture enters the main combustion chamber as a high energy flame jet, igniting the lean mixture in the main chamber. Typically, natural gas fuels both the main chamber and the PCC. In the current research, a mixture of reformed natural gas (syngas) and natural gas fuels the PCC. Syngas is a broad term that refers to a synthetic gaseous fuel. In this case, syngas specifically denotes a mixture of hydrogen, carbon monoxide, nitrogen, and methane generated in a natural gas reformer. Syngas has a faster flame speed and a wider equivalence ratio range of operation than methane. Fueling the PCC with Syngas reduces combustion instabilities and misfires. This extends the overall engine lean limit, enabling further NO_x reductions.Research results presented are aimed at quantifying the benefits of syngas PCC fueling. A model is developed to calculate the equivalence ratio in the PCC for different mixtures and flowrates of fuel. An electronic injection valve is used to supply the PCC with syngas. The delivery pressure, injection timing, and flow rate are varied to optimize PCC equivalence ratio. The experimental results show that supplying the PCC with 100% syngas improves combustion stability by 21% compared to natural gas PCC fueling. A comparison at equivalent combustion stability operating points between 100% syngas and natural gas shows an 87% reduction in NO_x emissions for 100% syngas PCC fueling compared to natural gas PCC fueling.     

An experimental investigation on the use of EGR in a supercharged natural gas SI engine

The use of lean burn technology in spark-ignition engines has been dominant; however, lean burn technique can not economically satisfy the increasingly restricted future emission standards. Consequently, alternative combustion techniques need to be investigated and developed. In this paper, the use of the stoichiometric air-fuel mixture with exhaust gas recirculation (EGR) technique in a spark-ignition natural gas engine was experimentally investigated. Engine performance and NO emissions were studied for both atmospheric and supercharged inlet conditions. It was found that the use of EGR has a significant effect on NO emissions. NO emissions decreased by about 50% when EGR dilution increased from zero with an inlet pressure of 101 kPa to close to the misfire limit with an inlet pressure of 113 kPa. In addition, the use of EGR effectively suppressed abnormal combustion which occurred at higher inlet pressure. The use of higher inlet pressure in the presence of EGR improved engine performance significantly. Engine brake power increased by about 20% and engine fuel consumption decreased by about 7% while NO emissions decreased by about 12% when 5% of EGR dilution was employed with an inlet pressure of 113 kPa compared to using undiluted stoichiometric inlet mixture with an inlet pressure of 101 kPa.     

Theoretical limits of scaling-down internal combustion engines

Small-scale energy conversion devices are being developed for a variety of applications; these include propulsion units for micro aerial vehicles (MAV). The high specific energy of hydrocarbon and hydrogen fuels, as compared to other energy storing means, like batteries, elastic elements, flywheels and pneumatics, appears to be an important advantage, and favors the ICE as a candidate. In addition, the specific power (power per mass of unit) of the ICE seems to be much higher than that of other candidates.However, micro ICE engines are not simply smaller versions of full-size engines. Physical processes such as combustion and gas exchange, are performed in regimes different from those that occur in full-size engines. Consequently, engine design principles are different at a fundamental level and have to be re-considered before they are applied to micro-engines. When a spark-ignition (SI) cycle is considered, part of the energy that is released during combustion is used to heat up the mixture in the quenching volume, and therefore the flame-zone temperature is lower and in some cases can theoretically fall below the self-sustained combustion temperature. Flame quenching thus seems to limit the minimum dimensions of a SI engine. This limit becomes irrelevant when a homogeneous-charge compression-ignition (HCCI) cycle is considered. In this case friction losses and charge leakage through the cylinder-piston gap become dominant, constrain the engine size and impose minimum engine speed limits.In the present work a phenomenological model has been developed to consider the relevant processes inside the cylinder of a homogeneous-charge compression-ignition (HCCI) engine. An approximated analytical solution is proposed to yield the lower possible limits of scaling-down HCCI cycle engines. We present a simple algebraic equation that shows the inter-relationships between the pertinent parameters and constitutes the lower possible miniaturization limits of IC engines.     

Performance and exhaust emission characteristics of a spark ignition engine using ethanol and ethanol-reformed gas

Since ethanol is a renewable source of energy and has lower carbon dioxide (CO₂) emissions than gasoline, ethanol produced from biomass is expected to be used more frequently as an alternative fuel. It is recognized that for spark ignition (SI) engines, ethanol has the advantages of high octane and high combustion speed and the disadvantage of ignition difficulties at low temperatures. An additional disadvantage is that ethanol may cause extra wear and corrosion of electric fuel pumps. On-board hydrogen production out of ethanol is an alternative plan.Ethanol has been used in Brazil as a passenger vehicle fuel since 1979, and more than six million vehicles on US highways are flexible fuel vehicles (FFVs). These vehicles can operate on E85 - a blend of 85% ethanol and 15% gasoline.This paper investigates the influence of ethanol fuel on SI engine performance, thermal efficiency and emissions. The combustion characteristics of hydrogen enriched gaseous fuel made from ethanol are also examined.Ethanol has excellent anti-knock qualities due to its high octane number and a high latent heat of evaporation, which makes the temperature of the intake manifold lower. In addition to the effect of latent heat of evaporation, the difference in combustion products compared with gasoline further decreases combustion temperature, thereby reducing cooling heat loss. Reductions in CO₂, nitrogen oxide (NOx), and total hydrocarbons (THC) combustion products for ethanol vs. gasoline are described.     

Recent advances in high temperature catalytic combustion

Catalytic combustion of methane has been investigated for the application to gas turbines. As the combustion is operated at high temperatures and high space velocity, heterogeneous reaction and surface-initiated gas phase reaction proceed concurrently. Thermal resistance to maintain large surface area is, therefore, requested to attain high combustion efficiency above 1000°C. Hexaaluminate compounds were effective in maintaining large surface area. On the other hand, palladium catalysts were generally employed for the combustion of methane below 1000°C. The prototype catalyst combustors were successfully tested with their high combustion efficiency and low NO_x emission by using Pd based- and/or hexaaluminate catalysts.     

Experimental investigation on the time resolved THC emission characteristics of liquid phase LPG injection (LPLi) engine during cold start

This work investigates the total hydrocarbon (THC) emission characteristics in a liquid phase LPG injection (LPLi) engines during cold start operation. To clarify the THC formation mechanism of the LPLi engines, the effect of various spark timings during cold start was investigated using a fast response THC analyzer and combustion analyzer. A cycle-to-cycle combustion analysis showed that the majority of THC emissions are emitted within the first few seconds after engine start. The emission results for vehicle test indicated that exhausted THC during phase 1 of FTP-75 mode decreased by 23% at top dead center (TDC) spark timing and by 31% at after top dead center (ATDC) 10° crank angle (CA) compared to that with a conventional spark timing of before top dead center 10° CA. In addition, catalyst light off times were shortened by 7 and 10 s in case of TDC and ATDC 10° CA spark timings, respectively. Consequently, it was founded that the control strategy of retarding spark timing during cold start in the LPLi vehicle was a very effective method to reduce THC emissions.     

The use of pure methanol as fuel at high compression ratio in a single cylinder gasoline engine

The methanol has greater resistance to knock and it emits lower emissions than neat gasoline. As single cylinder small engines have low compression ratio (CR), and they run with slightly rich mixture, their power are low and emission values are high. The performance can be increased at high CR if these engines are run with fuels which have high octane number. In this study, methanol was used at high CR to increase performance and decrease emissions of a single-cylinder engine. Initially, the engine whose CR was 6/1 was tested with gasoline and methanol at full load and various speeds. Then, the CR was raised from 6/1 to 8/1and 10/1, gradually. The knock was not observed at the CRs of 8/1 and 10/1 when using methanol while the knock was observed at the CR of 8/1 when using gasoline. The knock was determined from the cylinder pressure-time curves. The results showed that some decreases were obtained in CO, CO₂ and NO_x emissions without any noticeable power loss when using methanol at the CR of 6/1. By increasing the CR from 6/1 to 10/1 with methanol, the engine power and brake thermal efficiency increased by up to 14% and 36%, respectively. Moreover, CO, CO₂ and NO_x emissions were reduced by about 37%, 30% and 22%, respectively.     

乏风瓦斯流向变换催化燃烧试验研究

为实现低浓度瓦斯气体的高转化率,满足实际工程低温排气的要求,设计制作一套新型流向变换蓄热催化燃烧反应器,并利用模拟气体进行催化燃烧实验研究。结果表明,气体流量为70 L·min^-1、燃烧反应温度控制在500 ℃和甲烷体积分数为0.2%时,甲烷催化燃烧转化率超过80%,出口气体温度低于60 ℃。该系统能满足工程低温排气要求。