火花点火发动机准维湍流卷吸燃烧模型的适用性研究（二）

本文利用作者提出的火花点火发动机准维湍流卷吸燃烧模型，对压缩比为１０和１２的火球形燃烧室以及压缩比为１０的碗形燃烧室变工况进行了计算，将计算得到的示功图、质量燃烧率等与实验值进行了对比对分析。结果表明，合理选取与燃烧室结构相对应的四个经验常数，准维湍流卷吸燃烧模型完全适用于火花点火发动机变工况及不同燃烧室结构工作过程的计算，能够正确反映火花点火发动机结构参数和运转参数对燃烧过程的影响。     

火花点火发动机准维湍流卷吸燃烧模型的适用性研究（1）

本文在分析火花点火发动机湍流涡结构及缸内湍流特性参数的基础上，提出了适用于火花点火发动机燃烧计算的准维湍流卷吸模型，通过建立相应的子模型及求解方程，实现了燃烧过程的计算；对压缩比为１０的紧凑型燃烧室，在改变发动机转速、负荷、空燃比以及点火正时的情况下，计算得到的压力示功图、质量燃烧率等与实测值一致，从而证实了该模型的合理性。     

Characteristics of cyclic heat release variability in the transition from spark ignition to HCCI in a gasoline engine

We study selected examples of previously published cyclic heat-release measurements from a single-cylinder gasoline engine as stepwise valve timing adjustments were made to shift from spark ignited (SI) combustion to homogeneous charge compression ignition (HCCI). Wavelet analysis of the time series, combined with conventional statistics and multifractal analysis, revealed previously undocumented features in the combustion variability as the shift occurred. In the spark-ignition combustion mode, the heat-release variations were very small in amplitude and exhibited more persistent low-frequency oscillations with intermittent high-frequency bursts. In the HCCI combustion mode, the amplitude of the heat-release variations again was small and involved mainly low-frequency oscillations. At intermediate states between SI and HCCI, a wide range of very large-amplitude oscillations occurred, including both persistent low-frequency periodicities and intermittent high-frequency bursts. It appears from these results that real-time wavelet decomposition of engine cylinder pressure measurements may be useful for on-board tracking of SI–HCCI combustion regime shifts.     

多火花塞点火实现快速燃烧的试验研究

使用快速压缩-膨胀机改装的多火花塞点火试验台架,研究了火花塞数目对指示功大小、最高燃烧压力和最大压升率、燃料放热速率及爆震特性的影响。得到结果如下:液压源压力及混合气浓度相同,点火相位从上止点前5~35mm逐渐增大时,指示功先增大后减少,即存在最佳点火相位;随着火花数目的增加,最佳点火时刻后移;多火花塞点火的放热速率、最高燃烧压力和压升率、指示功均比单火花塞点火有明显提升,提升幅度和火花塞数目并不成线性关系;在混合气稀薄时,多火花塞点火对燃烧速率及指示功的提升作用更加明显;随着液压源压力的增大,相同点火相位时,多火花塞比单火花塞点火爆震倾向更加严重。     

关于火花点火发动机预混燃烧若干问题的研究进展

围绕降低火花点火发动机的有害排放和提高其经济性，内燃机工作者对火花点发动机的燃烧进行了大量的基础研究工作。本文对其中若干问题的研究现状与动态进行了综述，以期对火花点火发动机预混燃烧的基础研究有一个最基本的了解。     

火花点火对缸内直喷汽油机HCCI燃烧的影响

实现汽油机均质混合气压燃(HCCI)的难点是着火控制。在缸内直喷汽油机上实现了HCCI燃烧,研究了火花点火对HCCI燃烧特性的影响。结果表明,HCCI燃烧方式较火花点火(SI)火焰传播燃烧方式放热速率快,热效率高,NOx大幅度降低。在HCCI临界状态时,火花点火有助于提高燃烧稳定性,抑制失火和爆燃,降低循环波动;当火花点火时缸内温度远超过临界着火温度时,火花点火对HCCI燃烧影响不大。火花点火在SI／HCCI燃烧模式切换工况时,能提高瞬态过渡平顺性。     

Evaluation of a spark ignition engine cycle using first and second law analysis techniques

In the present work, a simulation model of the actual processes occurring during the thermodynamic cycle of a real spark ignition engine is developed. The model incorporates such important features as heat exchange of the cylinder gases with the chamber walls (during all phases), real spark ignition timings, real valve opening and closing timings, accurate simulation of the spherical flame front movement issuing from the spark plug and calculation of eight chemical species concentration during combustion, at every engine degree crank angle. The results from this first law analysis of the real cycle (for example pressure indicator diagrams, efficiencies) are compared favourably with the relevant experimental results obtained from a flexible, variable compression ratio, Ricardo E-6 spark ignition engine, located at the author's laboratory, forming thus a sound basis for moving towards a second law evaluation of this cycle. The thermodynamic state points, determined from the first law analysis, are used to determine the availability (second law analysis) at each engine crank angle and so lead to the effectiveness computation, as well as to the revelation of the magnitude of the work-potential lost during the various processes in a much more realistic way than the first law analysis can. The second law analysis results, for the actual engine in hand, are compared with the up-to-now existing ideal cycle Otto engine results. Also, a second law parametric investigation is performed over a wide range of design and operation conditions (compression ratio, fuel-air ratio, ignition advance), providing useful information for the cycle processes performance assessment by bringing state degradations and thermodynamic losses into perspective.     

火花点火发动机燃烧循环变动的理论研究

本文改进了一个火花点火发动机的准维计算模型，并对燃烧的循环变动进行了理论计算研究。这个模型包括点火时刻火花塞附近气流平均速度、湍流强度、气缸内残余废气系数以及缸内总的混合气质量等的循环变动的影响。将计算结果和试验结果进行了比较，证实了用这个模型可以较精确地预测燃烧的循环变动。另外，运用这个模型分别讨论了湍流强度、火焰中心位置在缸内的移动，以及残余废气系数的循环变动对不同燃烧阶段循环变动的影响程度，从而得出了一些有益的结论。     

Experimental investigation on effects of knocking on backfire and its control in a hydrogen fueled spark ignition engine

The experimental study was carried out on a multi-cylinder spark ignition engine fueled with hydrogen for analyzing the effect of knocking on backfire and its control by varying operating parameters. The experimental tests were conducted with constant speed at varied equivalence ratio. The equivalence ratio of 0.82 was identified as backfire occurring equivalence ratio (BOER). The backfire was identified by high pitched sound and rise in in-cylinder pressure during suction stroke. In order to analyze backfire at equivalence ratio of 0.82, the combustion analysis was carried out on cyclic basis. Based on the severity of in-cylinder pressure during suction stroke, the backfire can be divided into two categories namely low intensity backfire (LIB) and high intensity backfire (HIB). From this study, it is observed that there is frequent LIB in hydrogen fueled spark ignition engine during suction stroke, which promotes instable combustion and thus knocking at the end of compression stroke. This knocking creates high temperature sources in the combustion chamber and thus causes HIB to occur in the subsequent cycle. A notable salient point emerged from this study is that combustion with knocking can be linked with backfire as probability of backfire occurrence decreases with reduction in chances of knocking. Retarding spark timing and delaying injection timing of hydrogen were found to reduce the chances of backfire occurrence. The backfire limiting spark timing (BLST) and backfire limiting injection timing (BLIT) were found as 12 ⁰bTDC and 40 ⁰aTDC respectively.     

火花点火对CAI燃烧过程的影响

CAI燃烧具有高效节能和低NOx的优点,但CAI燃烧也存在燃烧始点和放热率难以控制的难点。通过添加火花点火的方法,在缸内制造热点,产生有助于CAI燃烧的着火条件,从而达到了控制CAI燃烧始点的目的。试验表明,在添加火花点火后,着火滞燃期明显缩短,CAI着火及燃烧更稳定,并对经济性有一定改善。火化辅助点火也有利于CAI运行范围向更低负荷方向拓展。因此,火花点火可以作为控制CAI燃烧的一种辅助手段。     

Study of the cycle-to-cycle variations of an internal combustion engine fuelled with natural gas/hydrogen blends from the diagnosis of combustion pressure

A methodology is presented for studying the influence of using alternative fuels on the cycle-to-cycle variations of a spark ignition engine which has been fuelled with mixtures of natural gas and hydrogen in different proportions (0–100%). The experimental facility consists of a single-cylindrical spark ignition engine coupled to an asynchronous machine with a constant engine rotation speed of 1500 rpm. A thermodynamic combustion diagnostic model based on genetic algorithms is used to evaluate the combustion chamber pressure data experimentally obtained in the mentioned engine. The model is used to make the pressure diagnosis of series of 830 consecutive engine cycles automatically, with a high grade of objectivity of the combustion analysis, since the relevant adjustment parameters (i.e. pressure offset, effective compression ratio, top dead center angular position, heat transfer coefficients) are calculated by the genetic algorithm. Results indicate that the combustion process is dominated by the turbulence inside the combustion chamber (generated during intake and compression), showing little dependency of combustion variation on the mixture composition. This becomes more evident when relevant combustion variables are plotted versus the Mass Fraction Burned of each mixture. The only exception is the case of 100% hydrogen, due to the inherent higher laminar speed of hydrogen that causes combustion acceleration and thus turbulence generation.     

Characterisation of laser ignition in hydrogen–air mixtures in a combustion bomb

Laser-induced spark ignition of lean hydrogen–air mixtures was experimentally investigated using nanosecond pulses generated by Q-switched Nd:YAG laser (wavelength 1064 nm) at initial pressure of 3 MPa and temperature 323 K in a constant volume combustion chamber. Laser ignition has several advantages over conventional ignition systems especially in internal combustion engines, hence it is necessary to characterise the combustion phenomena from start of plasma formation to end of combustion. In the present experimental investigation, the formation of laser plasma by spontaneous emission technique and subsequently developing flame kernel was measured. Initially, the plasma propagates towards the incoming laser. This backward moving plasma (towards the focusing lens) grows much faster than the forward moving plasma (along the direction of laser). A piezoelectric pressure transducer was used to measure the pressure rise in the combustion chamber. Hydrogen–air mixtures were also ignited using a spark plug under identical experimental conditions and results are compared with the laser ignition ones.     

Availability analysis of a coke oven gas fueled spark ignition engine

The current work investigates a coke oven gas fueled spark ignition (SI) engine from the perspective of the first and second laws in order to understand the energy conversion performance of fuels and achieve highly efficient utilization. A detailed energy and exergy analysis is applied to a quasi-dimensional two-zone spark ignition engine model which combines turbulence flame propagation speed model at 1500 rpm by changing gas fuel types, compression ratio, load and ignition timing. It was found that the irreversibility of methane is the maximum and that of syngas is the minimum among the three different fuels. The irreversibility in the combustion process of a coke oven gas fueled SI engine is reduced when the compression ratio or the throttle valve opening angle is increased and the ignition timing is delayed. Increasing the compression ratio and delaying the ignition timing can improve the first and second law efficiency and reduce the brake specific fuel consumption (BSFC). The power performance and fuel economy are good and the energy is also used effectively when the compression ratio is 11, the throttle angle is 90% and the ignition time is ?10° CA ATDC respectively.     

一种高效率的内燃机燃烧模式

本文探讨了以双燃料发动机为代表的预混合和扩散燃烧共存的复合燃烧模式。认为这种燃烧模式兼有预混合燃烧和扩散燃烧的优点，而且有比传统的燃烧模式更高的热效率。实验证明，采用这种燃烧模式工作的发动机可以有比火花点火式发动机更高的压缩比，有比压燃式发动机更高的燃烧速率。最后对这种发动机的燃烧特性及获得较高热效率的原因进行了分析。     

A computational study and correlation of premixed isooctane–air laminar reaction front properties under spark ignited and spark assisted compression ignition engine conditions

To address the need for reliable premixed laminar burning velocity and thickness information within the spark assisted compression ignition (SACI) combustion regime, a large dataset of simulated reaction fronts has been generated in this work. A transient one dimensional premixed laminar flame simulation was applied to isooctane–air mixtures using a 215 species chemical kinetic mechanism. The simulation was exercised over fuel–air equivalence ratios, unburned gas temperatures and pressures ranging from 0.1 to 1.0, 298 to 1000 K and 1 to 250 bar, respectively, a range that extends beyond that of previous researchers. Steady reaction fronts with burning velocities in excess of 5 cm/s could not be established under all of these conditions, especially when burned gas temperatures were below 1500 K and/or when characteristic reaction front times were on the order of the unburned gas ignition delay. Steady premixed laminar burning velocities were correlated using a modified two-equation form based upon the asymptotic structure of a laminar flame, which produced an average error of 2.5% between the simulated and correlated laminar burning velocities, with a standard deviation of 3.0%. Additional correlations were constructed for reaction front thickness and adiabatic flame temperature. The resulting premixed laminar burning velocity correlation showed good agreement with experiments and existing correlations within the spark-ignited (SI) regime. Analysis of the simulated characteristic reaction front times and ignition delays suggests that homogeneous SACI combustion is most useful under medium and high load operating conditions.     

Advancing lean combustion of hydrogen-air mixtures by laser-induced spark ignition

We investigate how ignition through laser-induced plasma can improve the application of lean combustion, in particular in environmental conditions relevant to hydrogen internal combustion engines (ICE). Major design goals when developing combustion engines are increasing thermal efficiency and decreasing combustion emissions. High compression ratios, lean combustion and precise ignition timings are contributing factors in ICE optimization. In our studies, several gains from laser spark ignition are investigated. The high energy content of laser-induced ignition kernels are shown to speed up the development of the early flame kernels. These extended ignition kernels transfer into self propagating flames even in lean mixtures. Leaner mixtures are ignited in our experiments using laser spark ignition in comparison to conventional electrical spark plugs. Precise ignition timing is realized. Multi-point ignitions are synchronized on the timescale of microseconds to enhance the progress of combustion. We modified the locus of ignition in a mixture flow to decrease the temporal extent of flame contact with the wall. Therefore, burning duration and heat loss can be reduced.     

一种新的燃烧方式——均匀充量压缩着火的研究进展

本文分析了均质充量压缩着火的特点，国外将均质充理压缩着火方式应用于往复式发动机中的研究现状，阐述了燃料系统的设计，并探讨了在我国开展均质充量压缩着火研究工作的必要性和方案。     

Evaluation of acetylene as a spark ignition engine fuel

In spite of its known shortcomings as a fuel for spark ignition engines, acetylene has been suggested as a possible alternative to petroleum-based fuels since it can be produced from non-petroleum resources (coal, limestone and water). Therefore, acetylene was evaluated in a single-cylinder engine to investigate performance and emission characteristics with special emphasis on lean operation for NO_x control. Testing was carried out at constant speed, constant airflow and MBT spark timing. Equivalence ratio and compression ratio were the primary variables. The engine operated much leaner when fuelled with acetylene than with gasoline. With acetylene, the engine operated at equivalence ratios as lean as 0·53 and 0·43 for compression ratios of 4 and 6, respectively. However, the operating range was very limited. Knock-induced preignition occurred either with compression ratios above 6 or with mixtures richer than 0·69 equivalence ratio. Both the indicated thermal efficiency and power output were less for acetylene fuelling than for gasoline. Acetylene combustion occurred at sufficiently lean equivalence ratios to produce very low NO_x and CO emissions. However, when the low NO_x levels were achieved hydrocarbon control was not improved over that with gasoline. Despite the potential for NO_x control demonstrated in this study of acetylene fuelling, difficulties encountered with engine knock and preignition plus well-known safety problems (wide flammability limits and explosive decomposition) associated with acetylene render this fuel impractical for spark ignition engines.     

一种新的燃烧方式——均匀充量压缩着火的研究进展

分析均质充量压缩着火的特点,国外将均质充量压缩着火方式应用于往复式发动机中的研究现状,阐述燃料系统的设计,并探讨在我国开展均质充量压缩着火研究工作的必要性和方案。     

Numerical investigation of a large bore,direct injection,spark ignition,hydrogen-fuelled engine

This paper presents Unsteady Reynolds Averaged Navier Stokes (URANS) simulations of a large bore, hydrogen-fuelled direct injection spark ignition (DISI) engine at different spark and start of injection (SOI) timings. Six cases are simulated, including three with various spark timings at a low boost level and three with advanced to late injection timings at a higher boost level. The numerical simulations are validated with experimental data for four out of six cases, while the other two are considered blind computational fluid dynamics (CFD) simulations. It is shown that the autoignition occurs with advanced spark timing due to high in-cylinder pressure and unburnt temperature. For different SOIs, it is demonstrated that flame propagation involves a spark-initiated flame combined with an autoignition generated flame. The case with the late injection timing features poor mixing and slower combustion due to the presence of lean mixtures near the spark plug. As a result, this case features the lowest thermal efficiency when SOI is varied. In all cases, both mixture and temperature stratification are present. Simulations of zero-dimensional chemical reactors demonstrate that this stratification must be correctly captured for accurate prediction of autoignition timing.