High Cyclic Variability Research Articles

Determination of cyclic air-fuel ratio and analysis of low and high-frequency variations in dual-fuel RCCI engine

Higher cyclic variations (CVs) in the engine affect the performance, emissions and drivability of the vehicle. Higher CVs are one of the challenges in dual-fuel reactivity-controlled compression ignition (RCCI) engines, mainly at lower loads. Cyclic disparities in the charge preparation, such as air-fuel ratio (AFR), result in CVs in the combustion parameters. The pressure moment method (PMM) is employed in the gasoline/methanol-diesel RCCI engine to estimate cyclic disparities in AFR. The logged cyclic in-cylinder pressure is used to calculate the cyclic AFR. After determining the cyclic AFR, statistical analysis and return maps are applied for the analyses of variations in the AFR, CA10, CA50, pmax and IMEP. For examining the low and high-frequency disparities in cyclic [Formula: see text] and its relationship with CA10, Wavelet transform (WT) is further applied. A good relationship is found between the estimated mean AFR and the experimental mean AFR. Return maps signify that for the earlier start of injection (SOI), the data points of AFR are more scattered correspondingly, the data points for CA10, CA50, pmax and IMEP are more scattered. WT analysis shows that both high-frequency and low-frequency variations are present in dual-fuel RCCI combustion. It is found that high-frequency discrepancies in the AFR are consistent throughout the engine cycles for all the tested injection timings. Wavelet results confirm that high-frequency fluctuations in AFR result in disparities in CA10 and IMEP.

Cyclic Variability Analysis of an Engine Fueled With Gasoline/Natural Gas Using Return Maps and Symbol Sequences

Abstract The present work investigates the cyclic variability of a single-cylinder spark ignition engine fueled with gasoline/natural gas. Return maps and symbol sequence analysis are used to analyze the cycle dynamics at different engine loads and mixture strength. Cycle dynamics is found to be stochastic in nature at high engine loads with low cyclic variability. The frequency of deterministic patterns with close coupling between consecutive cycles is found to be high at low loads with high cyclic variability. In comparison to gasoline, the deterministic effects are found to be more predominant for natural gas fueled engine. The paper also demonstrates that the identification of deterministic patterns and omitting them through an efficient engine management system brings the engine to a stable state from unstable state. The research provides an estimate of how much better engine performance could be achieved with the knowledge of determinism in the system and the subsequent application of this knowledge for efficient engine control.

Effects of split diesel injection strategies on combustion, knocking, cyclic variations and emissions of a natural gas-diesel dual fuel medium speed engine

Accelerated by the harms and depletion risk of fossil fuels, transition to low-carbon or renewable fuels have become an urgent need for combustion engines to decarbonize transport sectors. Natural gas-diesel dual-fuel combustion is a promising method to achieve these goals by allowing the usage of natural gas in diesel engines. However, this concept has drawbacks of low combustion efficiency, high unburned hydrocarbon (HC) emissions and high cyclic variations at low engine loads. These drawbacks hinder the benefits of dual-fuel such as low NOx and soot emissions. To find solutions to these drawbacks, split diesel injections with variable injection timings and mass split ratios (ratio of first injection diesel mass to total diesel mass) were investigated experimentally and numerically on a medium speed marine engine at low load using constant natural gas and diesel amounts.Experimental results of the split injection were compared to single injection dual-fuel and conventional diesel operation. Single injection case resulted in slightly lower HC emissions and cyclic variations and higher NOx emissions than split cases in a narrow injection timing interval. Apart from that, split injections increased combustion efficiency and decreased cyclic variations in a broader timing interval. For split cases, early first injection timing prevented high premixed heat release peak, suppressed NOx emissions and knocking. Especially, using 70% split ratio with retarded second injections increased combustion efficiency, decreased knocking level and provided simultaneous reduction of HC and NOx emissions compared to lower split ratio cases. In short, despite not giving the minimum values at all conditions, split injection showed potential to find a remedy to high HC emissions and cyclic variations issues by keeping robust operation in a wider injection timing interval.The numerical results support the experiments in which better combustion and decreased HC emissions are attained using sufficiently early diesel injections. Simulations show that, compared to late single injection, early single injection dual-fuel case enables more homogeneous temperature distribution and better oxidization of methane near the cylinder wall and central region above the piston crown. Besides, split injection shows improved methane oxidation near the cylinder wall and inside top-land crevice volume.

Chemical Effect of DME on the Combustion and Heat Release of SI-CAI Hybrid Combustion Based on Micro Flame Ignition Strategy

ABSTRACT Gasoline SI-CAI combustion has shown its advantages in expanding the operating range of high-efficiency combustion. However, the high cyclic variation occurs since the presence of exhaust gas limits the spark ignition and its controllability by auto-ignition. To further improve the stability and reliability of hybrid combustion, MFI (Micro Flame Ignition) strategy has been proposed. Although the phenomenon of MFI hybrid combustion was learned before, the chemical effect of high-activity fuel DME (Dimethyl Ether) and its inter-reaction with gasoline to the combustion process has yet to be studied. In this paper, the carbon tracer method was used to separate the reaction of DME and gasoline in CFD (Computational Fluid Dynamics) simulation, and chemical reaction kinetic analysis was carried out. The congregate DME could produce formaldehyde by 2-step oxidation of DME spontaneously, which led to a high flame speed than the spark ignition. The discrete MFI strategy showed a two-times flame speed ignited by the spark plug, which led to the mid-product of gasoline enhancing the first step of DME oxidation. Although the discrete DME showed high chemical activity in the whole cylinder, the high temperature and pressure caused by DME’s auto-ignition led to a shorter ignition delay for the auto-ignition process in the congregate MFI strategy.

Experimental investigation into the effects of Argemone biodiesel/diesel blends on cyclic variations in a multi-cylinder CRDI engine

Abstract Internal combustion engines suffer from high cyclic variations that result in higher emissions, lower efficiency, higher fuel consumption and poor drivability. The purpose of this study is to investigate how Argemone mexicana biodiesel (AGB)/diesel blended fuels affect the cyclic variability of combustion parameters such as maximum cylinder pressure (Pmax) and indicated mean effective pressure (IMEP) in a four-cylinder turbocharged intercooled common-rail direct injection engine under various engine loading conditions. The chemical and physical properties of AGB produced from A. mexicana oil were measured and compared according to the ASTM D6751 standards. In various volumetric ratios, AGB and diesel fuel were blended as D100, AB10 (10% AGB + 90% D100), AB20 (20% AGB + 80% D100) and AB30 (30% AGB + 70% D100). The IMEP and Pmax time-series data were collected over 200 consecutive cycles at low, partial and high engine loads at a constant engine speed of 2000 rpm. The coefficients of variation (COV) of combustion parameters (Pmax and IMEP) were measured for different AGB/diesel blends and found to be within acceptable limits. The results show that COVPmax and COVIMEP decrease as the engine load increases. It was observed that at low load, AB10 has the lowest COV (Pmax, IMEP), and at partial and high load, AB20 has the lowest COV (Pmax, IMEP) among all the blends.

Effect of coil charge duration on combustion variability and flame morphology in a GDI engine working in lean burn conditions

Spark ignition (SI) and subsequent flame front development exert a significant influence on cyclic variability of internal combustion engines (ICEs). The increasing exploitation of lean air-fuel mixtures in SI engines to lower fuel consumption and CO2 emissions is driving the scientific community towards the search for innovative combustion strategies. Moreover, although lean combustion has been widely investigated and an important number of studies is already present in literature, the high cyclic variability typical of this combustion process still represents a major hinder to its exploitation. This study aims to investigate the effects of increasing ignition energy on combustion characteristics of lean mixtures. Tests were performed on an optically accessible gasoline direct injection (GDI) engine that allowed to investigate the correlation between the thermodynamic results and spark arc-flame morphology. Engine speed was fixed at 2000 rpm, a relative air fuel ratio (AFRrel) of about 1.3 was selected and ignition timing was set at 12 crank angle degrees (CAD) bTDC. Coil charge duration was swept from 10 to 40 CAD. Two intake pressure levels were investigated, the first corresponding to wide open throttle under naturally aspirated operating mode, the second with an intake pressure of 1.2 bar, thus corresponding to a boosted operating condition. Two dedicated scripts built using NI Vision were employed for image processing, allowing the evaluation of temporal and spatial evolution of the early stages of combustion. Arc elongation and flame front contour were used as correlation parameters that characterize flame kernel inception and development. The results confirm that, as expected, the increase of the coil charge duration tends to reduce cyclic variability in terms of engine output. The optical investigations revealed that for both examined cases the standard deviation related to the wrinkling effect on flame edge at CA5 decreased as the coil charge duration increased.

In-cylinder pressure statistical analysis and digital signal processing methods for studying the combustion of a natural gas/diesel heavy-duty engine at low load conditions

In-cylinder pressure analysis is one of the most important tools for combustion diagnosis. The dual-fuel compression ignition engines present a different in-cylinder pressure evolution for consecutive cycles due to the high cyclic variability. One source of the cyclic variability is a long ignition delay caused by a low-temperature combustion chamber (at low load conditions) and this effect led to lower efficiency, higher emissions, and driveability problems. In the present study, a six-cylinder turbocharged heavy-duty diesel engine (6.7 L) was used to acquire the in-cylinder pressure signal at low-load operating conditions. Then a statistical methodology is proposed to process the experimental pressure signal for a combustion diagnosis approach obtained at different loads for diesel mode and dual fuel mode. First, a representative sample number of consecutive thermodynamic cycles is determined, and then the cut-off frequencies for in-cylinder pressure signal digital filtering are selected by the analysis of the Fourier Transform spectrum for the test engine using only diesel fuel and natural gas/diesel mode. The results show an effective high-frequency noise diminish (related to the resonance combustion chamber) on the filtered pressure signals. Therefore, a high-quality curve of the heat release rate can be reached, which allows identifying the combustion process at low-loads operating conditions.

A study on the effect of qualitative control coupling variable engine speed on the hydrogen-fueled Wankel rotary engine at wide-open throttle

Hydrogen-fueled Wankel rotary engine, with few available research currently, has excellent power and emission characteristics, however, with lower efficiency. With increasing attention to low-carbon emission, it is of great significance to explore methods to improve the efficiency of hydrogen-fueled Wankel rotary engines. This work aims to study the effect of qualitative control coupling variable engine speeds at the wide-open throttle on the power control. The comparative effect of qualitative control coupling engine speeds from 1000 r/min to 1500 r/min under the wide-open throttle and quantitative control at 1500 r/min on the combustion and emission characteristic of hydrogen-fueled Wankel rotary engine is investigated. The results show that compared with quantitative control, qualitative control coupling variable engine speed can achieve excellent performance. The brake thermal efficiency can be maximally increased by 43.5%, an absolute increase of 6.22%, as well the volumetric efficiency with a maximal 105% improvement. The thermal load and risk of knock can be greatly reduced. Moreover, NO emission also can be reduced by more than an order of magnitude or even by zero. Although there is an increase in cyclic variation, the value is no more than 4%. In addition, qualitative control coupling variable engine speed allows flexible matching of appropriate engine speed and excess air ratio based on the actual requirements of efficiency, stability, durability and emission. • The power control method of the hydrogen Wankel rotary engine is investigated. • Qualitative control achieves better engine performance than quantitative control. • Qualitative control coupling engine speed meets the power and high-efficiency demand. • Lower thermal load, knock tendency and NO emission can be obtained. • Much high excess air ratio isn't recommended due to high cyclic variation.

Machine Learning-based Classification of Combustion Events in an RCCI Engine Using Heat Release Rate Shapes

Reactivity controlled compression ignition (RCCI) mode offers high thermal efficiency and low nitrogen oxides (NOx) and soot emissions. However, high cyclic variability at low engine load and high pressure rise rates at high loads limit RCCI operation. Therefore, it is important to control the combustion event in an RCCI engines to prevent abnormal engine combustion. To this end, combustion in RCCI mode was studied by analyzing the heat release rates calculated from the in-cylinder pressure data at 798 different operating conditions. Five distinct heat release shapes are identified. These different heat release traces were characterized based on start of combustion, burn duration, combustion phasing, maximum pressure rise rate, maximum amount of heat release, maximum in-cylinder gas temperature and pressure. Both supervised and unsupervised machine learning approaches are used to classify different types of heat release rates. K-means clustering, an unsupervised algorithm, could not cluster the heat release traces distinctly. Convolution neural network (CNN) and decision trees, supervised classification algorithms, were designed to classify the heat release rates. The CNN algorithm showed 70% accuracy in predicting the shapes of heat release rates while decision tree resulted in 74.5% accuracy in predicting different heat release rate traces.

Cycle-to-cycle variability in spark-assisted compression ignition engines near optimal mean combustion phasing

Stoichiometric spark-assisted compression ignition (SACI) combustion with exhaust gas recirculation (EGR) dilution has demonstrated higher part-load thermal efficiencies compared to spark-ignited engines, while maintaining ultra-low tailpipe emissions. However, SACI is often characterized by high cyclic variability in heat release or torque output, which poses a challenge to its implementation in light-duty vehicles. This paper presents an experimental investigation of cyclic variability in stoichiometric SACI combustion under EGR-dilute conditions, while maintaining mean combustion phasing (θ50) near optimal timing for thermal efficiency. The present work focuses on SACI conditions where the flame-based heat release fraction is between approximately 10% and 40% of the overall heat release, and therefore contributes significantly to the combustion process. For the SACI conditions examined, the variability in θ50 was driven by variability in autoignition timing, which in turn correlated with the start of measurable heat release (θ02). High variability in θ50 caused unstable work output due to very late combustion with poor or no end-gas autoignition. The use of a high ignition energy dual-coil offset ignition system had negligible impact in reducing θ50 variability. Analysis of experimental data from close to 1000 operating conditions showed that the magnitude of θ50 variability correlates with the flame-based heat release fraction ([Formula: see text]), for a large range of intake pressures, spark timings and exhaust gas recirculation levels. For the SACI conditions examined, combustion phasing variability was largely determined by flame-based combustion and particularly the initial flame formation (θIGN-02), and minimally by the end-gas autoignition heat release. The analysis also demonstrated that θ50 variability is amplified as the contribution of the flame to the overall heat release increases.

The Application of Flame Image Velocimetry to After-injection Effects on Flow Fields in a Small-Bore Diesel Engine

This study implements Flame Image Velocimetry (FIV), a diagnostic technique based on post-processing of high-speed soot luminosity images, to show the in-flame flow field development impacted by after-injection in a single-cylinder, small-bore optical diesel engine. Two after-injection cases with different dwell times between the main injection and after-injection, namely, close-coupled and long-dwell, as well as a main-injection-only case are compared regarding flow fields, flow vector magnitude, and turbulence intensity distribution. For each case, high-speed soot luminosity movies from 100 individual combustion cycles are recorded at a high frame rate of 45 kHz for FIV processing. The Reynolds decomposition using a spatial filtering method is applied to the obtained flow vectors so that bulk flow structures and turbulence intensity distributions can be discussed. The results show significant after-injection-induced flow structures as a group of vectors travelling back toward the center of the combustion chamber upon the jet impingement on the piston bowl wall and then jet-to-jet collision. Despite higher cyclic variations caused by the after-injection, increased bulk flow magnitude and turbulence intensity upon the after-injection event suggests locally enhanced mixing. Compared to the long-dwell after-injection, the close-coupled after-injection shows more significant turbulence enhancements.

An avant garde study on design and analysis of honey comb structured piston

Weight reduction of the engine is one of the methods that affect lower fuel consumption reduction. The piston is one of the primary parts in an automobile engine and the performance of the piston has a direct impact on performance of the engine. It is also subjected to high thermal load, mechanical load and cyclic variation which affect the fatigue life of the piston. Honeycomb structure is artificial structure having similar geometry of natural honeycomb. This particular structure enables minimization of material consumption there by reducing the weight and also the cost. The honeycomb structure will be a hexagonal in shape and provides relatively higher compression properties and load bearing capacity. To reduce the fuel consumption by means of weight reduction and to achieve the same level of loading capacity, the honeycomb structure is very opt one. In this paper, the geometric model and analysis of piston was developed using Dassault systems solid works corporation by considering generative structural analysis. In the present work aims an avant garde study on design and analysis of honeycomb structured piston for commercial vehicle TVS scooty pep model of Indian automotive vehicle.

Homogeneous charge compression ignition combustion stability improvement using a rapid ignition system

When compared to traditional engines, homogeneous charge compression ignition has the potential to significantly reduce NO x raw emissions, while maintaining a high fuel efficiency. Homogeneous charge compression ignition is characterized by compression-induced autoignition of a lean homogeneous air–fuel mixture. Since homogeneous charge compression ignition does not utilize direct ignition control, it is strongly dependent on the state of the cylinder charge and can suffer from high cyclic variability. With spark-assisted compression ignition, it has been demonstrated that misfires can be reduced, while preserving the high thermal efficiency of homogeneous charge compression ignition as a result of the more favorable physical mixture properties due to dilution. However, spark-assisted compression ignition reduces the NO x benefits of homogeneous charge compression ignition, as it increases the local combustion temperatures. To merge the advantages of the homogeneous charge compression ignition and the spark-assisted compression ignition combustion processes, a field-programmable gate array for detailed simulation of the physical gas exchange is combined with a rapid spark system. The low latency and computational speed of the field-programmable gate array allows the simulation process to be implemented in real time. When combined with the rapid reaction time of the high-frequency current-based rapid ignition system, a feedforward controller based on the cylinder pressure or heat release is realized. The developed model-based controller determines if a spark is required to assist the homogeneous charge compression ignition combustion process. The use of the field-programmable gate array and rapid ignition system allows for the calculation of combustion properties and controller output within 0.1 °CA. This article presents the development and experimental validation of the developed controller on a single-cylinder research engine. The combustion stability has been significantly improved as reflected in an improved standard deviation of the indicated mean effective pressure and a reduction of the combustion phasing variations. Furthermore, compared to a traditional homogeneous charge compression ignition system, the hydrocarbon emissions can be reduced, while maintaining low NO x emissions.

Impact of methane energy fraction on emissions, performance and cyclic variability in low-load dual fuel combustion at early injection timings

This work experimentally examines the effect of methane (a natural gas surrogate) substitution on early injection dual fuel combustion at representative low loads of 3.3 and 5.0 bar BMEPs in a single-cylinder compression ignition engine. Gaseous methane fumigated into the intake manifold at various methane energy fractions was ignited using a high-pressure diesel pilot injection at 310 °CA. For the 3.3 bar BMEP, methane energy fraction sweeps from 50% to 90% were performed; while at 5.0 bar BMEP, methane energy fraction sweeps from 70% to 90% were performed. It is observed that minimum methane energy fraction is limited by maximum pressure rise rate leading to knock and maximum methane energy fraction is limited by a high coefficient of variation in netIMEP, which leads to high cyclic variations. For 3.3 bar BMEP, maximum pressure rise rate is 8 bar/°CA at 50% methane energy fraction while at 5 bar BMEP, it is 12 bar/°CA at 70% methane energy fraction. For 3.3 bar BMEP, engine-out NOx emissions decrease by 43 times when methane energy fraction increases from 50% to 90%, and it decreases by nearly 46 times when methane energy fraction increases from 70% to 90% at 5 bar BMEP. Engine-out unburned hydrocarbon emissions increase by nearly 9 times when methane energy fraction increases from 50% to 90% at 3.3 bar BMEP, and it increases by nearly 5 times when methane energy fraction increases from 70% to 90% at 5.0 bar BMEP. Engine-out carbon monoxide emissions increase by nearly 7 times when methane energy fraction increases from 50% to 90% at 3.3 bar BMEP and by nearly 5 times when methane energy fraction increases from 70% to 90% at 5.0 bar BMEP. In addition, cyclic combustion variations at both loads were analyzed to obtain further insights into the combustion process and identify opportunities to further improve fuel conversion efficiencies at low load operation.

Investigation of cyclic variations in air-fuel ratio, cylinder wall temperature, and residual gas fraction of a dual fuel compression ignition engine

Dual fuel operation in compression ignition engines is an effective way to reduce the NOx emission. Within the certain range of fuel premixing ratio (PR), the dual fuel operation in CI-engines results in improved thermal efficiency. The dual fuel CI-engine has relatively higher cyclic variations in comparison to conventional CI-engine which limits the range of fuel premixing in dual fuel CI-engine. The cyclic variations in air-fuel ratio, cylinder wall temperature, and residual gas fraction are the major factors, which governs the variations in combustion parameters. The cyclic variations in combustion need to control for stable engine operation. The present study estimates the cyclic air-fuel ratio, cylinder wall temperature, and residual gas fraction from the measured in-cylinder pressure data of dual-fuel CI-engine. The experiments are performed on a modified single cylinder CI-engine equipped with a separate port fuel injector and its controller to operate an engine in dual fuel mode. In this study, 1500 consecutive engine cycles are recorded, and air-fuel ratio, cylinder wall temperature, and the residual gas fraction is estimated for each cycle. Pressure moment method is used to estimate the cyclic air-fuel ratio. The cyclic cylinder wall temperature is calculated by determining the inversion angle. The cyclic variations are analyzed using statistical methods.

Multi-point micro-flame ignited hybrid lean-burn combustion of gasoline with direct injection dimethyl ether

Lean-burn combustion is effective in reducing fuel consumption of gasoline engines because of the higher specific heat ratio of the fuel lean mixture and reduced heat loss from lower combustion temperature. However, its application to real engines is hampered by the unstable ignition, high cyclic variability, and partial-burn due to slower combustion, as well as the restricted maximum lean-burn air/fuel ratio limit and the insufficiently low nitrogen oxides emission. Multi-point micro-flame-ignited hybrid combustion has been proposed and applied to extend the lean burn limit of premixed gasoline and air mixture. To achieve micro-flame-ignited combustion in premixed lean gasoline mixture formed by port fuel injection, a small amount of dimethyl ether is injected directly into the cylinder of a four-stroke gasoline engine to control and accelerate the ignition and combustion process so that the engine could be operated with the overall excess air coefficient (Lambda) of 1.9. The results show that heat release processes can be grouped into three forms, that is, ramp type, double-peak type, and trapezoid type. Regardless of single or split injections, direct injection timing of dimethyl ether dominates the features of heat release. The ramp type occurs at early injection timing while the double-peak type takes place at late injection timing. Trapezoid type appears between the above two types. Dimethyl ether injection timing controls the ignition timing and has less effect on combustion duration. Single injection of dimethyl ether leads to much earlier ignition timing and slightly longer combustion duration, forming higher nitrogen oxides emissions than the split injections. Ultra-low nitrogen oxides emissions and higher thermal efficiency are achieved in the ramp type combustion compared to the other two types of combustion in both injection approaches.

Development and experimental validation of a field programmable gate array–based in-cycle direct water injection control strategy for homogeneous charge compression ignition combustion stability

Homogeneous charge compression ignition is a part-load combustion method, which can significantly reduce oxides of nitrogen (NO x) emissions compared to current lean-burn spark ignition engines. The challenge with homogeneous charge compression ignition combustion is the high cyclic variation due to the lack of direct ignition control. A fully variable electromagnetic valve train provides the internal exhaust gas recirculation through negative valve overlap which is required to obtain the necessary thermal energy to enable homogeneous charge compression ignition. This also increases the cyclic coupling as residual gas and unburnt fuel is transferred between cycles through exhaust gas recirculation. To improve combustion stability, an experimentally validated feed-forward water injection controller is presented. Utilizing the low latency and rapid calculation rate of a field programmable gate array, a real-time calculation of residual fuel mass is implemented on a prototyping engine controller. Using this field programmable gate array–based calculation, it is possible to calculate the amount of fuel and the required control interaction during an engine cycle. This controller prevents early rapid combustion following a late combustion cycle using direct water injection to cool the cylinder charge and counter the additional thermal energy from any residual fuel that is transferred between cycles. By cooling the trapped cylinder mass, the upcoming combustion phasing can be delayed to the desired setpoint. The controller was tested at several operating points and showed an improvement in the combustion stability as shown by a reduction in the standard deviation of combustion phasing and indicated mean effective pressure.

Evaluation of engine combustion and exhaust emissions characteristics using diesel/butanol blended fuel

Depletion of non-renewable fuel sources accompanied with never-ending engine exhaust emissions pollution from internal combustion lead to renewed interests in alternative energy resources. Alcohol fuel had emerged as one of the viable candidates as a fuel substitute to reduce the use of fossil fuels in diesel engine. The aim of the experimental investigation is to study the effects of engine fuel properties characteristics towards engine combustion and exhaust emissions characteristics. In this experimental study, the diesel engine was tested at butanol/diesel percentage volume ratios of 5:95 (DBu5), 10:90 (DBu10) and 15:85 (DBu15) of butanol-to-diesel, respectively. Combustion analysis results showed that butanol/diesel blends have a lower in-cylinder pressure, rate of pressure rise and rate of heat release. Moreover, the mass fraction burned analysis shows longer ignition delay and burn duration. Apart from that, the wavelet power spectrum analysis suggested that DBu15 possesses high engine cyclic variations. The engine exhaust emissions show generally a reduction of nitrogen oxides, carbon monoxides and unburned hydrocarbon.

Wavelet analysis of an SI engine cycle-to-cycle variations fuelled with the blending of gasoline -fusel oil at a various water content

Cycle to cycle variation of a spark ignition engine is analyzed utilising wavelet analysis technique based on the spectral-temporal approach to stabilizing high cyclic variations. The selected examples of previously published cyclic IMEP measurements from a DISI engine a different percentage of fusel oil blended with gasoline (FAWE10, FAWE20, FBWE10 and FBWE20) under 4500 rpm engine speed and 60% WOT are studied. The results reveal that the increase in spectral power is observed with increasing fusel oil up to 20% with both blends (FBWE20 and FAWE20). The indicates a pronounced influence of fusel oil ratio on the engine CCV of IMEP. However, the maximum peak in GWS observed for FBWE20 fuel blend with more uniform overall spectral power for FAWE20 fuel blend which indicates a noticeable enhancement in cyclic variations behaviour after water extraction. As an outcome, the fusel oil water content has acted negatively to restrict the combustion as the fusel oil increased as well as the cyclic variations affected despite the high oxygen content and octane number of fusel oil.

Load limits of an HCCI engine fueled with natural gas, ethanol, and methanol

Low Temperature combustion (LTC) engines are able to reduce NOx and particulate matter (PM) emissions, simultaneously. But, this combustion process generally leads to higher amounts of HC and CO emissions. Furthermore, higher cyclic variation (misfire) especially at low engine loads as well as high pressure rise rate (knock) at high loads situations, are the main obstacles to application of this concept. Therefore, fuels with good auto-ignition specification (i.e. lower octane numbers) are suitable for low load conditions, while for high load situations, fuels with higher octane numbers are required. In the current study, three fuels with different octane numbers (i.e. natural gas, ethanol and methanol) are experimentally investigated in a single cylinder engine to explore proper operating range for each fuel. Achievements suggested that natural gas is the proper fuel for HCCI strategy at higher intake temperatures and rich mixture conditions (i.e. high loads) while ethanol and methanol are good choices for lower intake temperatures and lean mixtures (i.e. low loads). Results revealed that for the mixtures with the equivalence ratios more than 0.3 (φ > 0.3) and intake temperatures higher than 430 K (Tivc > 430 K), natural gas is a suitable choice, while at this situation, ethanol and methanol lead to knock and also unacceptable level of NOx emission. Ethanol has good performance for 0.2 < φ < 0.3 and Tivc < 430 K, while methanol is applicable even for ultra-lean mixtures (φ ≈ 0.1). These results highlight the use of flex fuel vehicles (FFVs) idea for current engine.