HCCI Combustion Process Research Articles

Availability analysis of n-heptane/iso-octane blends during low-temperature engine combustion using a single-zone combustion model

A zero-dimensional single-zone combustion and an availability balance model for low temperature combustion (LTC) engines have been developed combined with skeleton mechanism of primary reference fuel and the first and second law of thermodynamics. The variation of system availability is analyzed, and the effects of nine major species (OH, CH2O, H2O2, C3H6, C8H18, C7H16, CO, CO2, H2O) on availability conversion are studied. The influences of fuel octane number on the availability of LTC process are studied to investigate the effects of fuel characteristics on availability destruction of HCCI combustion process. The irreversibility increases and heat transfer availability decreases with the rise of iso-octane volume fraction in primary reference fuels (PRFs).

Global Reduced Model for Conventional and Alternative Jet and Diesel Fuel Autoignition

A global reduced model for the autoignition of conventional petroleum-derived and alternative, hydroprocessed and Fischer–Tropsch, jet and diesel fuels is presented. The model is based on a seven-step model from the literature (Zheng, J.; Miller, D. L.; Cernansky, N. P. A Global Reaction Model for the HCCI Combustion Process, SAE Paper 2004-01-2950, 2004) and includes steps to predict oxidation and autoignition in the three temperature regimes of interest to engine applications, the high-, low-, and negative-temperature-coefficient (NTC) regimes. Here we have included dependence of reaction rate parameters on the derived cetane number (DCN) to predict the influence of fuel variability on autoignition and optimized the reduced model to best fit target shock tube ignition delay time data for jet and diesel fuels. The standard deviation between model predictions for ignition delay and the target shock tube data set is ±21% and the model captures all experimental trends for ignition delay variation with DCN, temperature, pressure, and fuel–air equivalence ratio in all temperature regimes. Comparisons to experimental ignition delay time data not contained in the target data set show model–experiment deviation similar to the comparisons with the target data, with global standard deviation of ±20–30% and differences of at most a factor of 2. The model comparisons with shock tube data suggest that the model is suitable for autoignition prediction for fuels containing large quantities of aliphatic compounds with DCN = 30–80 for 650–1300 K, 8–80 atm, and fuel–air equivalence ratios of 0.25–1.5.

EGR および過給がHCCI 燃焼過程におよぼす影響 ― n-Heptane を対象にした素反応数値計算 ―

EGR および過給がHCCI 燃焼過程におよぼす影響 ― n-Heptane を対象にした素反応数値計算 ―

A Study of HCCI Combustion Using In-Cylinder Flame Visualization and Ultraviolet Absorption Spectroscopy (Understanding the Rapid HCCI Combustion by Observing the In-Cylinder Flame Behavior)

This study investigated the characteristics of the HCCI combustion process in detail by means of in-cylinder visualization of the entire bore area and ultraviolet absorption spectroscopic measurement in the combustion chamber. Special attention was focused on the influence of the equivalence ratio and ignition timing on the degree of local dispersion of autoignition and resultant rapid combustion. The results made clear the relationship between the production/consumption of formaldehyde (HCHO) in the autoignition process and flame development behavior in the combustion chamber. Additionally, it was found that changes in the equivalence ratio and/or ignition timing significantly influenced the degree of local dispersion of the autoignited flame in the combustion chamber. As a result, some cases showed rapid combustion accompanied by in-cylinder pressure oscillations.

MD2-5 An Investigation of DME HCCI Combustion Using Spectroscopic Analysis(MD: Measurement and Diagnostics,General Session Papers)

In order to control the ignition timing and overall combustion rate of HCCI, it is important to have a firm understanding of the chemical reactions of fuel because HCCI can be characterized as controlled chemical auto-ignition process. One technique that can be employed to gain a better understanding of the HCCI combustion process is chemiluminescence, which is the light emission from the excited state of intermediates or radicals. The objective of this study is to experimentally investigate the correlation between chemiluminescence of the active species, which play important role in the ignition, and HCCI combustion characteristics for providing the way to control auto-ignition process. In addition, a combination of experimental and computational results is employed. The experiments were conducted using optical accessible engine, photo-multiplier and band-pass filters. Senkin application of the CHEMKIN-II kinetics rate code was used for computation. As the result, there was a precise correlation between the rate of heat release and chemiluminescence intensity of OH (307.4 nm) and all band (350-700 nm) by tracing the in-cylinder mass-averaged. The start timing of emitting luminescence in OH coincided with H_2O_2 dissociation, and the peak timing of emitting luminescence in all band corresponded to the CO-O recombination spectrum.

Experimental analysis of low temperature combustion mode with diesel and biodiesel fuels: A method for reducing NOx and soot emissions

One of the main advantages of biodiesel fuels is that almost eliminate carbon dioxide emissions based on the CO2 consumption during plant growth. However it is accepted for most researchers that when burned in diesel engines there is an increase of the NOx emissions when these are compared to the NOx emissions produced by mineral diesel fuel.HCCI with diesel fuel is being considered as an alternative combustion process in the internal combustion engine, mainly because of the huge potential for simultaneous reduction of NOx and soot emissions while fuel conversion efficiency is not compromised, in fact, it is usually increased.The HCCI combustion process can accept a variety of fuel types, like biodiesel and mixtures with mineral diesel fuel. The main reason for burning biodiesel fuel in HCCI combustion mode is that it enables the simultaneous reduction of NOx and soot emissions to current standard requirements, as well as the elimination of CO2.This paper shows a methodology for HCCI combustion mode of biodiesel mixtures based on a high swirl ratio and EGR rate combined with late injection where HRR, NOx, CO, HC and soot emissions have been analyzed. This strategy has reduced fuel wall impingement encountered when early injection is used. Bowl in piston geometry has been designed with a dedicated swirling flow model and a NOx emission of biodiesel fuel has been reduced.

Effects of temperature inhomogeneities on the HCCI combustion in an optical engine

Abstract This work investigated the influence of temperature inhomogeneities on the HCCI combustion process through an optically accessible engine. Temperature inhomogeneities were formed by changes in piston bowl geometries, intake temperatures, coolant temperatures. Results showed that combustion chamber geometry could play an important role in HCCI combustion. The autoignition for the reentrant bowl (A-type) combustion chamber always occurred at the center of the combustion chamber even with different intake temperatures and coolant temperatures. However, the autoignition for salient bowl (V-type) combustion chamber was more dispersive and closer to the chamber wall compared to A-type. For the V-type combustion chamber, the peak value of the heat release rate and the pressure rise rate was the highest and the combustion duration was the shortest among three cases, because of the piston bowl forming a lower turbulence intensity; while A-type combustion chamber induced a higher turbulence intensity, which enhanced the temperature inhomogeneities in the piston bowl, leading to moderate pressure rise rate and heat release rate. Turbulence intensity control offered a potentially effective approach to modulating the combustion process in HCCI engines.

이차원발광화상계측에 의한 예혼합압축자기착화연소의 연소실내 혼합기의 불균질성에 관한 연구

HCCI엔진에는 농도성층화와 열적성층화가 존재하고, 이것들은 착화와 연소과정에 영향을 미치고 있다. 본 연구에서는 예혼합기의 불균질성이 HCCI연소과정에 미치는 영향에 대해서 조사하였다. 우선 4행정광학엔진을 이용하여 잔류가스가 있는 경우와 급속압축장치를 이용하여 잔류가스가 없는 경우의 예혼합기의 불균질성에 대하여 비교분석하였다. DME를 연료로 이용하고 프래밍카메라를 사용하여 2차원화학발광이미지를 취득하였다. 그 결과, 잔류가스가 있는 불균질 한 경우에 4행정엔진실험에서는 연소현상이 공간적으로 연소현상의 시간차이가 발생하였다. 잔류가스가 없는 급속압축장치의 실험에서는 4행정기관의 결과에 비해서 더 적은 공간적인 변화가 존재하는 것을 알 수 있었다.

HC2-3: A Study of Autoignition in an HCCI Engine by using Light Absorption and Emission Spectroscopy(HC: HCCI Combustion,General Session Papers)

This research examined the effect of the residual gas condition on the HCCI combustion process, about which there have been many unclear points heretofore. Specifically, the influence of the residual gas condition on low-temperature reactions, ignition and the combustion state following ignition was investigated. A spectroscopic measurement technique was used to investigate the effect on low-temperature reactions. By analyzing the emission and absorption spectra, the formation behavior and wavelength bands of the chemical species produced during low-temperature reactions were made clear. In other words, the use of emission and absorption spectroscopic measurements provides a method for ascertaining the activity level of low-temperature reactions.

Investigation of a high efficient Free Piston Linear Generator with variable Stroke and variable Compression Ratio A new Approach for Free Piston Engines

Chemical energy can be converted to electricity with very high efficiencies by means of a free piston linear generator allowing a variable stroke and a variable compression ratio. Therefore online-downsizing in part-load is possible by reducing the stroke. As a result throttling, wall and friction losses are reduced. The paper describes the concept of the free piston linear generator, which is well suited for the HCCI-combustion process. It is expected that emissions and the fuel-consumption can be noticeable reduced. Calculations based on the NEDC indicate significant fuel savings for a mid-class car. Because of the non-existing mechanical coupling, cylinder cut-off can be realized very easily reducing the consumption of high power cars especially in urban drive cycles. The components linear generator and the gas spring have been built up and tested successfully. Examinations of the combustion process have begun on a fully variable electromagnetic valve-train test stand. A sophisticated adaptive control scheme is presented providing solid controls for the free-piston system. The paper describes the current status of the hardware development.

Numerical study on the chemical reaction kinetics of n-heptane for HCCI combustion process

The combustion mechanism of n-heptane have been investigated using a zero-dimensional thermodynamic model coupled with a detailed kinetic model. At low temperature reaction, the main initial reactions are NC 7H 16 + O 2 = C 7H 15-2 + HO 2 and NC 7H 16 + O 2 = C 7H 15-3 + HO 2. H-atom abstraction from n-heptane occurs primarily by OH and HO 2. The first O 2 addition and the second O 2 addition are the most important paths for the low temperature branching. High temperature reaction includes two stages: blue-flame reaction and hot-flame reaction. Blue-flame reaction which is controlled by H 2O 2 decomposition is mainly the process of the conversion of CH 2O to CO by reactions CH 2O + OH = HCO + H 2O and HCO + O 2 = CO + HO 2. Hot-flame reaction which is dominated by reaction H + O 2 = O + OH is mainly the process of the oxidization of CO to CO 2 by reaction CO + OH = CO 2 + H. There are four regions for HCCI combustion including: I complete combustion region; II high CO emissions region where low-temperature reaction and blue-flame reaction occur; III high CH 2O emissions region where only low-temperature reaction occurs and IV misfire region.

Analysis of the Effect of Charge Inhomogeneity of Fuel Distribution on the Ignition and Combustion in HCCI Engine by Chemiluminescence Measurement

In HCCI Engine, inhomogeneity of fuel distribution and temperature in pre-mixture microscopically exists and has possibility to affect the ignition and combustion process. In this study, the effect of charge inhomogeneity of fuel distribution on the HCCI combustion process was investigated. Pressure profiles were measured and two dimensional chemiluminescence images were captured by using a framing camera with a 4-stroke optical access engine. DME was used as the test fuel. Changing the way of mixing air and fuel in the intake manifold, inhomogeneity of fuel distribution in the pre-mixture was varied. The result showed that luminescence started and stopped at the same instant in whole the combustion chamber on the homogeneous condition. On the other hand, on the inhomogeneous condition luminescence started with a spatial variation in the combustion chamber. However local luminescence duration was almost the same on both conditions. It is clarified that a time lag appears spatially in combustion in the chamber on the inhomogeneous condition.

The effects of non-uniform temperature distribution on the ignition of a lean homogeneous hydrogen–air mixture

To characterize the ignition process in homogeneous charge compression ignition engines, high fidelity simulations are performed to study the effects of different initial temperature distributions on the autoignition of a turbulent homogeneous mixture at high pressure. The effects of the initial temperature distribution on the ignition and subsequent heat release are studied by comparison of simulations with three initial random temperature fields having different skewness. It is found that the scalar mixing and turbulence have a significant influence on the initial location and further evolution of the ignition kernels. A comparison of the integrated heat release rates shows that the presence of a hot core leads to early ignition and increased duration of burning, while a cold core leads to a dormant end gas, which is consumed by slow combustion. The extent of flame fronts is quantified by a temperature gradient cut-off, revealing distinct behavior in the appearance of flame fronts for the three cases. Finally, two distinct ignition regimes, namely the spontaneous propagation and the deflagration regimes, are identified, and a predictive criterion is defined based on the spontaneous propagation speed and deflagration speed at the local mixture conditions. The predictions are found to be consistent with the observed results, suggesting a potential strategy in the modeling of HCCI combustion process.