Combustion Variability Research Articles

Experimental study of combustion and cyclic variations in a CRDI engine fueled with heptanol/iso-propanol/butanol and diesel blends

The present study experimentally investigates main combustion, fuel injection, and cycle-by-cycle variations in a CRDI diesel engine fueled with blends of heptanol/iso-propanol/butanol and diesel. Two percentages of diesel and higher alcohol blends, denoted as D85HIB15 (85% diesel, 5% heptanol, 5% iso-propanol, 5% butanol) and D70HIB30 (70% diesel, 10% heptanol, 10% iso-propanol, 10% butanol), were utilized in the engine at different BMEPs (3.4, 5.2, and 6.9 bar). With increasing ratio of the alcohol blends in diesel, it was founded lower CPmax, PRRmax, and IMEP, prolonged ignition delay, earlier injection timing and combustion center, and also higher injection pressure compared to diesel fuel. Based on the standard deviation and coefficient of variation for 200 consecutive combustion data, diesel-HIB blends showed lower cyclic variations than conventional diesel under all test cases. Notable fluctuations in cycle-by-cycle injection pressure highlighted to cyclic combustion fluctuations. Finally, the relationship between main combustion parameters showed that the highest correlation was around 0.8 between CPmax and PRRmax for diesel-HIB blends at low load, and for pure diesel and D85HIB15 at medium load, indicating that there was a well linear relationship.

ANALYSIS OF IN-CYLINDER FLOW FIELDS USING PROPER ORTHOGONAL DECOMPOSITION-BASED QUADRUPLE DECOMPOSITION

In order to meet increasingly stringent emission norms coupled with a heightened requirement of performance, there has been an unabated effort toward improvement in the combustion process of modern internal combustion engines. One of the major impediments of enhanced combustion in spark-ignited port fueled engines are combustion variations. These variations are especially dominant at low-load, low-speed operations. Cycle-to-cycle variation (CCV) in in-cylinder flow fields is one of the major contributors of such combustion variations. Therefore, in this work, CCV of in-cylinder flow fields of an optical port fuel injection engine was analyzed at part load (50% throttle opening) and low speed (1200 rpm) with the help of proper orthogonal decomposition. Flow fields were subsequently decomposed into four components, namely, mean, coherent, transition, and turbulent parts. CCV of flow fields was studied using several metrics based on kinetic energy and the relevance index. It was found that the share of mean energy is a better metric for CCV quantification based on kinetic energy. Interestingly, it was observed that the mean part, though consistent in its flow structure for various cycles, has a lot of variation in kinetic energy at early compression stroke. Also, a weak mean flow coupled with a strong coherent flow structure opposing the mean flow produces the largest deviation in a flow field from its corresponding ensemble-averaged field. Furthermore, even though the coherent and transition parts are comprised of comparable energy, it was the coherent part that showed large variations in kinetic energy. Hence, the mean and coherent parts are mainly responsible for CCV in flow fields.

Cyclic Combustion Variability of Dimethyl-Ether-Fueled Agricultural Tractor Engine

Abstract Combustion in dimethyl-ether (DME)-fueled engines needs to be assessed carefully for its widespread acceptability from a drivability viewpoint. Since the test engine used in an off-highway segment, it was tested in a steady-state cycle for engine performance, combustion, emissions, and their cyclic variations, which were the only parameters to assess the drivability. This study investigated and analyzed the cyclic variations of a 100% DME-fueled engine equipped with modified mechanical fuel injection equipment. It was compared with baseline diesel to understand its positive and negative aspects. Experiments were conducted at different engine speeds (1200,1600, and 2000 rpm) and loads (No Load, 1.29, 2.59, 3.88, 5.18, and 6.47 bar brake mean effective pressure (BMEP)) . In-cylinder pressure was recorded for 250 consecutive engine cycles, and many combustion parameters were comparatively analyzed for diesel and DME fuelings. The coefficient of variation (COV) of maximum in-cylinder pressure (Pmax) was lower for DME than diesel at 1600 rpm and comparable at the other remaining engine speeds (1200 and 2000 rpm). Variations in COV of Pmax were higher at low loads and negligible at high loads for both test fuels. At 2000 rpm, the crank angle positions at which Pmax occurred were distributed in a narrow range for DME, representing higher combustion stability than baseline diesel. Variations in the maximum rate of pressure rise (RoPRmax) were lower for DME at 3.88 and 6.47 bar BMEP, while these were higher at 1.29 bar BMEP than baseline diesel. COV of indicated mean effective pressure (COVIMEP) decreased from lower to higher loads for diesel and DME fueling at 1600 and 2000 rpm engine speeds. The differences in COVIMEP between diesel and DME were negligible at higher loads, representing engine stability similar to baseline diesel. Combustion parameters assessed indicated that DME fueling led to lower cyclic variations than baseline diesel as the engine operated from lower to higher loads. At lower loads, DME fueling showed higher cyclic variations than baseline diesel.

Species, abundance, time of appearance of fly larvas in white rats (Rattus norvegicus Berkenhout 1769) carcass with different burnt times

The use of insects in determining PMI is still little. The flies during the period of laying eggs and forming larvae can estimate the time of death. This study aims to determine the type, abundance, and time of appearance of fly larvae on white rat carcasses that were treated with burning. The experiment was conducted on 12 female white rats of the wistar strain, aged 2-3 months, healthy, and weighing 150-200 g. The research was experimental which consisted of 4 treatments with 3 repetitions of each treatment. The treatment was given by first anesthetizing the rats using 10% ether, then dislocating the cervical spine. After being sacrificed, the rats were burned using stainless tongs over a fire with variations in burning time, namely A (10 minutes), B (20 minutes), and C (30 minutes). The carcasses of each treatment were placed in an open field with a distance of 2.5 meters between the carcasses. Observations were made for 5 days until the carcass underwent complete decomposition. Larvae were taken from each carcass using tweezers, then put into vials containing 70% alcohol. The larvae were then identified morphologically in the laboratory. There were types of fly larvae found in the burnt treated white rat carcasses, namely Sarcophaga argyrostoma and S. haemorrhoidalis, while the controls were Chrysomya albiceps, C. megacephala, and C. bezziana. S. argyrostoma was found with the highest abundance in the treatment (39.9 individuals), while C. albiceps was found in the control (346.2 individuals). The first fly larvae that appeared in the burning treatment were S. argyrostoma (31 hours) and those of the control C. megacephala (31 hours). The conclusion of this study is that the variation of combustion has or does not affect the type, abundance, and time of appearance of fly larvae on the carcass.

Investigating the Origins of Cyclic Variability in Internal Combustion Engines Using Wall-Resolved Large Eddy Simulations

Abstract Modern internal combustion engines (ICE) operate at the ragged edge of stable operation characterized by high cycle-to-cycle variations (CCV). A key scientific challenge for ICE is the understanding, modeling, and control of CCV in engine performance, which can contribute to partial burns, misfire, and knock. The objective of this study is to use high-fidelity numerical simulations to improve the understanding of the causes of CCV. Nek5000, a leading high-order spectral element, open source code, is used to simulate the turbulent flow in the engine combustion chamber. Multicycle, wall-resolved large-eddy simulations (LESs) are performed for the General Motors (GM), Transparent Combustion Chamber (TCC-III) optical engine under motored operating conditions. The mean and root-mean-square (rms) of the in-cylinder flow fields at various piston positions are validated using particle image velocimetry (PIV) measurements during the intake and compression strokes. The large-scale flow structures, including the swirl and tumble flow patterns, are analyzed in detail and the causes for cyclic variabilities in these flow features are explained. The energy distribution across the different scales of the flow are quantified using one-dimensional (1D) energy spectra, and the effect of the tumble breakdown process on the energy distribution is examined. The insights from this study can help us develop improved engine designs with reduced cyclic variabilities in the in-cylinder flow leading to enhanced engine performance.

Cycle-based LQG knock control using identified exhaust temperature model

Spark ignition engines are often desired to be operated close to their knock borderline when MBT (maximum brake torque) cannot be achieved for optimizing combustion efficiency. Under this circumstance, a calibrated baseline spark timing, along with other control parameters such as intake and exhaust valve timings, is found for the engine control system to maximize fuel economy, and a stochastic scheme can be used for the control based on a large number of history data. However, cycle-to-cycle combustion variations still exist, resulting in a relatively conservative baseline control. To reduce cycle-to-cycle combustion variations, a real-time cycle-wised knock compensation is required. The correlation between exhaust temperature at the current cycle and knock intensity at the next cycle was found in our earlier research. In this paper, a cycle-to-cycle spark timing compensation scheme is developed based on the measured exhaust temperature when the engine is operated close to its knock borderline. To make model-based control possible, [Formula: see text]-Markov COVER (COVariance Equivalent Realization) system identification was used to obtain a linearized engine exhaust system model from incremental spark timing to associated exhaust temperature and knock intensity. Accordingly, a Linear–Quadratic–Gaussian (LQG) controller is designed, based on the identified model, to minimize the knock intensity fluctuations based on incremental exhaust temperature variation. The LQG control strategy was integrated with the existing entire knock control architecture, where the baseline spark timing is generated based on the offline machine training with an online updating scheme developed earlier, and demonstrated experimentally. Note that the cycle-based compensation only adds incremental spark timing to the baseline control so that knock combustion variations can be reduced. Three test scenarios are used to demonstrate the effectiveness of the proposed cycle-to-cycle compensation scheme when the engine is knock-limited. With the help of cycle-to-cycle based compensation, it was demonstrated that engine spark timing can be further advanced about one crank degree while maintaining the same knock intensity up-limit due to reduced knock combustion variations. Note that this is corresponding to 0.5%–1.0% fuel economy for this engine when it is operated under knock condition.

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.

Analysis of performance, emissions, and lubrication in a spark-ignition engine fueled with hydrogen gas mixtures

Hydrogen is one of the main alternative fuels with the greatest potential to replace fossil fuels due to its renewable and environmentally friendly nature. Due to this, the present investigation aims to evaluate the combustion characteristics, performance parameters, emissions, and variations in the characteristics of the lubricating oil. The investigation was conducted in a spark-ignition engine fueled by gasoline and hydrogen gas. Four engine load conditions (25%, 50%, 75%, and 100%) and three hydrogen gas mass concentration conditions (3%, 6%, and 9%) were defined for the study. The investigation results allowed to demonstrate that the injection of hydrogen gas in the gasoline engine causes an increase of 3.2% and 4.0% in the maximum values of combustion pressure and heat release rates. Additionally, hydrogen causes a 2.9% increase in engine BTE. Hydrogen’s more efficient combustion process allowed for reducing CO, HC, and smoke opacity emissions. However, hydrogen gas causes an additional increase of 14.5% and 30.4% in reducing the kinematic viscosity and the total base number of the lubricating oil. In addition, there was evidence of an increase in the concentration of wear debris, such as Fe and Cu, which implies higher rates of wear in the engine’s internal components.

Effect of ammonia energy fractions on combustion stability and engine characteristics of gaseous (ammonia/methane) fuelled spark ignition engine

Non-carbon nature and higher hydrogen energy density of ammonia have gained a lot of interest as an energy asset and green fuel. In this work, the effects of ammonia fuel share and engine operating load on the combustion stability and engine characteristics (combustion and performance) of gaseous (NH3/CH4) fuelled SI engine have been reported. The lower heating value and flame propagation speed of fuel mixture reduce with the increase in ammonia share (0–60% at 8 Nm engine load) and thus results in detrimental engine performance and higher cycle-to-cycle combustion variations (1.36%–14.9% COV of IMEP). A rise in operating load from 8 Nm to 16 Nm increases the flame propagation speed of the fuel mixture (60% ammonia share) and improves engine performance and combustion stability (14.9%–4.3% COV of IMEP). The results of this study indicate that the substitution of methane with ammonia could be maximized at higher engine operating loads to get the benefit of clean fuel utilization.

Hydrogen-diesel dual-fuel direct-injection (H2DDI) combustion under compression-ignition engine conditions

This study investigates the ignition and combustion characteristics of interacting diesel-pilot and hydrogen (H2) jets under simulated compression-ignition engine conditions. Two converging single-hole injectors were used to inject H2 and diesel-pilot jets into an optically accessible constant-volume combustion chamber (CVCC). The parameters varied include fuel injection sequence, timing between injections, and ambient temperature (780–890 K). The results indicate that when diesel-pilot is injected before H2, with increasing time separation, the burnt diesel products mix and cool down, requiring longer jet-jet interaction to ignite the H2 jet. When H2 is injected before diesel-pilot, the H2-air mixing amount prior to pilot-fuel igniting impacts the combustion spreading through the H2 jet. If ignition of the H2 jet occurs beyond its end-of-injection (EOI), the H2 mixture zone where the pilot-diesel interacts with becomes too lean for combustion. At lower ambient temperatures, the combustion variability increases, attributed to the diesel-pilot lean out.

Multi-scale dynamics for a lean-burn spark ignition natural gas engine under low load conditions

This work investigates the multi-scale dynamics of the combustion system in a lean-burn spark ignition natural gas engine using different gas injection timings (GIT). The in-cylinder pressure time series are measured, and the indicated mean effective pressure (IMEP) time series are calculated. The influence of GIT on the combustion system is investigated through wavelet analysis, multi-resolution analysis, and the return maps with the GIT covering from 0 to 90°CA after top dead center at the intake stage. Results show that the combustion system has multi-scale chaotic characteristics, and it is sensitive to the change of GIT. The unreasonable GIT will result in serious combustion variations. Meanwhile, the combustion instability of the engine evolves on multiple time scales, showing evident multi-scale oscillation characteristics. All the wavelet power spectrums (WPS) present the characteristics of intermittent short-time periodic oscillations and persistent large-scale periodic oscillations concealed inside the IMEP time series. When the GIT approaches the medium value, the persistence of large-scale periodic oscillations is weakened, while the characteristics of high-frequency intermittent oscillations are enhanced. Under all working conditions, the contribution rate of high-frequency signal D1 decomposed by the IMEP time series to the overall time series fluctuation is about 40% or even higher. The contribution rate of the signal D1 also increases with the aggravation of combustion instability. The return map structures of high-frequency signals D1 and D2 show bifurcation structures, and the bifurcation characteristics of the signal D1 are more evident under medium GIT conditions, indicating a certain correlation between the 2–8 engine cycles, and the correlation between the adjacent engine cycles is stronger. The deterministic relationship between the multiple engine cycles found can help in developing a more reasonable and efficient combustion control strategy, which provides a theoretical basis for improving the stability of a natural gas engine.

Understanding the combustion mode transition from CDC to RCCI and RCCI to CDC – An experimental approach

This article presents an experimental understanding of combustion mode transition from conventional diesel combustion (CDC) mode to reactivity-controlled compression ignition (RCCI) combustion mode. In the current study the variations in combustion, performance, and emissions during the mode transition were investigated and accordingly a dual fuel control algorithm for achieving smooth transition between CDC and RCCI combustion modes was developed. Experimental data are presented for CDC with diesel and RCCI with Gasoline/Diesel at 1600 rev/min, 25 N.m torque only, considering the data size and ease of understanding the mode transition. Nine steps have been adopted to switch from CDC to RCCI combustion mode. The operating variables such as number of diesel injections, injected diesel mass between the injections, gasoline energy fraction, diesel start of injection, and exhaust gas recirculation (EGR) flow rate have been altered to switch from CDC to RCCI. Changes in combustion, performance, and emissions have been recorded and analyzed at each operating variable to determine the optimal path for smooth combustion mode transition. A similar approach has been extended to medium and high loads to obtain the optimal path. Finally, all the optimal paths have been collated to develop calibrated maps for operating the chosen test engine from CDC to RCCI and RCCI to CDC modes smoothly.

Effects of direct injection and mixture enleament on the combustion of hydrous ethanol and an ethanol-gasoline blend in an optical engine

Ethanol is a renewable fuel and can be used in electric hybrid vehicles concepts, especially for countries capable of producing such fuel in a sustainable way. A strategy to enhance these concepts is the use of lean-burn combustion, which is an effective way to improve the fuel economy from spark-ignition engines, while obtaining low pollutant emissions. However, these improvements are complicated to achieve in a practical way because lean combustion has low rates of reaction, extinction, and misfire cycles, leading to cyclical variability for the engine operation. The drawback becomes even greater when lean combustion is associated with commercial ethanol fuels and direct injection. Therefore, the objective of the present work is to provide an experimental analysis of spray guided direct injection with commercial fuels used in a consolidated market for the use of ethanol such as the Brazilian one, in particular hydrous ethanol (E95W05) and ethanol-gasoline blends (E27G73). The experiments were conducted in an optically accessible spark-ignition engine and the lean combustion effects on engine cycle variability, performance, flame morphology, and exhaust emissions were assessed. In general, the results indicated that combustion instabilities can be correlated from thermodynamic and optical analyses. Flame instabilities for E95W05 were associated with the lower flame propagation speed caused by the temperature reduction during lean combustion. Additionally, exhaust emissions contained the presence of unburned ethanol which increased when combustion became leaner. Moreover, the lower flame propagation speed was one of the factors responsible for reducing engine performance and increasing combustion variability. The results indicated that vaporization was a relevant phenomenon affecting ethanol combustion in the direct injection mode. The cooling effect of fuel vaporization presented itself as a powerful means for the reduction of NOx and aldehydes, even for the lean operation. Higher emissions of CO and THC were also observed for the engine operating with E95W05 when compared to E27G73. The results of the present work showed that special attention must be paid to the use of commercial fuel with a high ethanol content in spray-guided direct injection engines, especially during lean-burn combustion, in order to not compromise the performance nor increase pollutant emissions.

Effects of intake charge temperature and relative air-fuel ratio on the deterministic characteristics of cyclic combustion dynamics of a HCCI engine

Homogenous charge compression ignition (HCCI) combustion can significantly reduce automotive pollution and increase the thermal efficiency of the engine. However, combustion phasing control is a major challenge in HCCI engines due to severe cyclic combustion variations. This study investigates the cyclic combustion dynamics of the HCCI engine using nonlinear dynamic methods such as return maps, recurrence plots (RPs), and recurrence quantitative analysis (RQA). Combustion stability and cyclic variations of HCCI combustion parameters were investigated on a modified four-stroke diesel engine. The experiments were conducted by varying relative air-fuel ratios ([Formula: see text]) and intake air temperatures ([Formula: see text]) at two engine speeds. In-cylinder pressure data of 2000 consecutive engine combustion cycles is logged for each test condition. In this study, deterministic characteristics of combustion phasing (CA50) and crank angle position of maximum cylinder pressure ([Formula: see text]) are investigated and compared by employing nonlinear dynamical methods. Return maps revealed that [Formula: see text] is having distinct and more frequently observed deterministic characteristics in comparison to CA50. Patterns in RPs showed a more persistent and sudden change in the combustion dynamics at higher engine speeds. Recurrence plot-based analysis found the existence of deterministic features in the combustion dynamics irrespective of the operating conditions. It was found using RQA parameters that the deterministic nature becomes stronger with a decrease in [Formula: see text] and any deviation in intermediate values of [Formula: see text]. Additionally, RQA measures advocate that CA50 has more deterministic characteristics at higher engine speed while [Formula: see text] at lower engine speed. Strong coupling and synchronization between [Formula: see text] and CA50 is indicated by cross-recurrence plots and CPR index when engine operated with a comparatively richer mixture.

Modelling Study of Cycle-To-Cycle Variations (CCV) in Spark Ignition (SI)-Controlled Auto-Ignition (CAI) Hybrid Combustion Engine by Using Reynolds-Averaged Navier–Stokes (RANS) and Large Eddy Simulation (LES)

The spark ignition (SI)-controlled auto-ignition (CAI) hybrid combustion is characterized by early flame propagation combustion and subsequent auto-ignition combustion. The application of combined SI–CAI hybrid combustion can be used to effectively extend the operating range of CAI combustion and achieve smooth transitions between SI and CAI combustion modes. However, SI–CAI hybrid combustion can produce significant cycle-to-cycle variations (CCV). In order to better understand the sources of CCV and minimize its occurrence, the large eddy simulation (LES) and Reynolds-averaged Navier–Stokes (RANS) approaches were employed in this study to model and understand the cyclic phenomenon of SI–CAI hybrid combustion. Both the multi-cycle LES and RANS simulations were analyzed against the experimental measurements in a single cylinder engine at 1500 rpm and a 5.43 bar average indicated the mean effective pressure (IMEP). The detailed analysis of the in-cylinder pressure traces, IMEP, in-cylinder peak pressure (PP), peak pressure rise rate (PPRR) and the crank angles with fuel mass burned fraction at 10%, 50%, 90% and mode transition was performed. The results indicate that overall, the adopted LES simulations could effectively predict the cyclic variations in the hybrid combustion observed in the experiments, while the RANS simulations failed to reproduce the cyclic characteristics at the chosen engine operating conditions. Based on the LES results, the correlation and visualization studies indicate that the cyclic variations in the local velocity around the spark plug lead to the variations in the early flame propagation, which in turn produce temperature fluctuations among the cycles and result in greater variations in the subsequent auto-ignition combustion events.

A New Simple Function for Combustion and Cyclic Variation Modeling in Supercharged Spark Ignition Engines

Research in the field of Internal Combustion (IC) engines focuses on the drastic reduction of both pollutant and greenhouse gas emissions. A promising alternative to gasoline and diesel fuel is represented by the use of gaseous fuels, above all green hydrogen but also Natural Gas (NG). In previous works, the authors investigated the performance, efficiency, and emissions of a supercharged Spark Ignition (SI) engine fueled with mixtures of gasoline and natural gas; a detailed research involving the combustion process of this kind of fuel mixture has been previously performed and a lot of experimental data have been collected. Combustion modeling is a fundamental tool in the design and optimization process of an IC engine. A simple way to simulate the combustion evolution is to implement a mathematical function that reproduces the mass fraction burned (MFB) profile; the most used for this purpose is the Wiebe function. In a previous work, the authors proposed an innovative mathematical model, the Hill function, that allowed a better interpolation of experimental MFB profiles when compared to the Wiebe function. In the research work presented here, both the traditional Wiebe and the innovative Hill function have been calibrated using experimental MFB profiles obtained from a supercharged SI engine fueled with mixtures of gasoline and natural gas in different proportions; the two calibrated functions have been implemented in a zero-dimensional (0-D) SI engine model and compared in terms of both Indicated Mean Effective Pressure (IMEP) and cyclic pressure variation prediction reliability. It was found that the Hill function allows a better IMEP prediction for all the operating conditions tested (several engine speeds, supercharging pressures, and fuel mixtures), with a maximum prediction error of 2.7% compared to 4.3% of the Wiebe function. A further analysis was also performed regarding the cyclic pressure variation that affects all the IC engines during combustion and may lead to irregular engine operation; in this case, the Hill function proved to better predict the cyclic pressure variation with respect to the Wiebe function.

Understanding the effect of turbulent flow on the combustion cyclic variation in a spark ignition engine using Large-Eddy simulation

At the present, emission regulations have been tightened around the world in an effort to reduce emissions from internal combustion engine (ICE) vehicles. The one of the issues in the development of eco-friendly spark ignition (SI) internal combustion engines is a cycle-to-cycle variation (CCV) of combustion. Therefore, research on the CCV is also being actively carried out. Because the causes that affect the cycle deviation are various and complex, it is difficult to conduct detailed research on the source of the CCV through experimental studies. Therefore, the 3D simulation, especially large-eddy simulation (LES) approach is actively carried out.In the present study, the Lagrangian ignition model developed for LES is introduced. The Lagrangian particles were employed to realize the ignition channel and the secondary electric circuit model was implemented to predict the spark energy and the end of ignition time. And 30 LES cycles were performed to identify the cause of the CCV and validated against the experimental data. The vortex produced by wall flow on the secondary tumble plane was identified as an important factor. A new piston shape was designed to strengthen the vortex formation by wall flow. The result of new piston case showed the reduced combustion CCV than the base case. This research provides the guide how to investigate the sources of the combustion CCV and how to reduce the combustion CCV for the future engine development.

Effects of pre-mixed gas composition on combustion characteristics of micro pilot dual fuel (MPDF) in a heavy-duty dual fuel engine

The effects of premixed gas compositions on the combustion characteristics in micro pilot duel fuel (MPDF) conditions were investigated. Propane, hydrogen, and carbon dioxide gases were added to methane gas, and engine experiments were conducted under various premixed gas compositions. A single-cylinder heavy-duty engine with a combustion chamber volume of 1100 mm3 and compression ratio of 17.0 was used. A 55 kW DC dynamometer was used to operate the single-cylinder dual-fuel engine at a constant engine speed. At high propane mixture ratios, knocking combustion occurred, accompanied by intense engine vibrations, owing to the low octane number of propane. Knocking combustion led to an increase in the combustion variation and ringing intensity (which represents the knocking combustion intensity). In contrast, at high ratios of hydrogen, which has a high octane number, knocking combustion was suppressed, and the speed of combustion was lower than that in the case of high propane mixture ratios. The optimum conditions corresponded to a ringing intensity of 3–5 MW/m2. The addition of even a small amount of propane gas enhanced the engine performances in misfiring conditions. In contrast, a considerable amount of hydrogen gas was required to prevent abnormal combustion because of the low density of hydrogen gas. The presence of carbon dioxide effectively stabilized MPDF combustion by suppressing knocking combustion.

Impacts of Al<sub>2</sub>O<sub>3</sub> nano additive and waste cooking biodiesel on performance and emission characteristics of CI engine

The running down of fossil fuel resources and strict regulation on emission parameters, it is essential to search for improved diesel engine performance and cleaner combustion. Elective energizes are the up-and-comer powers of the present and what is to come. An ever increasing number of vehicles are exchanging over to elective energizes around the world, demonstrates a definite indication of their need. It is clear that without alternative fuels, mankind will not have sustained eco-mobility in the future. Using additives will play a very good role in improving the performance and emissions. The effect of waste cooking oil biodiesel and Al<sub>2</sub>O<sub>3</sub> nano additives on the performance and emission of diesel engines are clearly discussed in this article. In this article mainly focused on waste cooking oil and effect of nano additives. The different properties of this fuel are evaluated using ASTM test standard and compared in relation to that of conventional diesel oil. All experimentation carried out on TV2, Kirloskar, single acting, 4-stroke, water cooled diesel motor having an evaluated yield of 16HP at 1800 rpm and a pressure proportion of 17.5:1, with varied load 0% to 100% of full load with increment of 20%. Waste cooking oil biodiesel and Al<sub>2</sub>O<sub>3</sub> nano additives shows marginal variation in performance, combustion and emission characteristic like (UBHC, CO, NO<sub>x</sub>) have been evaluated and compared to diesel

Wavelet analysis for cyclic combustion dynamics of a multi-cylinder CRDI diesel engine fuelled with a blending of argemone biodiesel-diesel oil.

Higher cyclic variability in combustion adversely influences emissions, efficiency, and driveability of internal combustion engines. In this paper, we used wavelet transform techniques to investigate the dynamical characteristics of a combustion process in numerous combustion parameters of a 4-cylinder turbocharged common rail direct injection (CRDI) diesel engine fuelled with Argemone mexicana biodiesel (AGB)/diesel blended fuel. In addition, statistical analysis is described to validate the results of the wavelet spectrum methods for cyclic variation in the diesel engine. The results show that the cyclic variations in IMEP and Pmax are sensitive to the engine load and fuel properties. The coefficient of variation of both combustion parameters decreases as engine load increases for all tested fuels. Moreover, adding Argemone mexicana biodiesel (AGB) into diesel fuel up to 20% (AB20) reduces cyclic variations in combustion parameters at all tested engine loads. Furthermore, the global wavelet spectrum and wavelet power spectrum are utilized to identify the dominant oscillatory combustion modes. The cycle-to-cycle fluctuations in combustion parameters (i.e., IMEP and Pmax) exhibit multi-scale dynamics for all experimental conditions. Compared to long and intermediate oscillations in diesel fuel, AB10 and AB20 fuel showed short and intermittent period fluctuations. The findings of this experimental work will be helpful to optimize engine control strategies for AGB/diesel blended fueled multi-cylinder CRDI diesel engines.