Engine Combustion Modes Research Articles

Engine behavior analysis on a conventional diesel engine combustion mode powered by low viscous cedarwood oil/waste cooking oil biodiesel/diesel fuel mixture – An experimental study

Binary biofuel is the best alternative source that completely replaces petroleum-based fuel. In this study, we have experimented with the waste cooking oil and cedarwood oil as biofuel in a DI CI engine for various proportions and related its combustion, emission, and performance characteristics to those of base diesel. This study aims to eliminate the utilization of fossil fuel in a diesel engine by introducing green binary fuel (low viscous fuel resulting from the blending of cedarwood oil with WCO biodiesel) successfully. The objective of the study is to convert cedarwood – WCO into green binary fuel and investigate its performance, emission, and combustion properties. The transesterification process is utilized for the enhancement of WCO as biodiesel. It occasioned a reduction in brake thermal efficiency as the addition of waste cooking oil in the blend increased. At the same time, the maximum value of BTE of 27.8% was attained for B10C90 (10% transesterified waste cooking oil and 90% cedarwood oil in volume), whereas it was 28.1% for diesel at maximum load conditions. The BSEC was 15.4 MJ/kW-hr for B10C90 and 12.8 MJ/kWhr for diesel. The emission characteristics, CO, HC, NOx, CO2, and smoke for B10C90 were 17.93 g/kWhr, 0.55 g/kWhr., 20.09 g/kWhr, 2210.9 g/kWhr, and 25.55%. Combustion features such as NHRR, burn duration, MPRR, combustion efficiency, Ignition delay, and coefficient of variance for B10C90 were 53.74 bar, 29.38 CAD, 4.71 bar/CAD, 99.7%, 7.01 CAD, and 4.73% respectively. It showed that B10C90 had comparable performance (BTE) and combustion values to mineral diesel with better emission characteristics.

Impact of exhaust gas recirculation and nitric oxide on the autoignition of an oxygenated gasoline: Experiments and kinetic modelling

Exhaust gas recirculation (EGR) and NOx affect the autoignition of gasoline in internal combustion engines. In this work, ignition delay times of an oxygenated gasoline (Euro 6 E10) are investigated with EGR and NOx addition. The experimental data are of interest for gasoline surrogate modeling and for predicting fuel ignition behavior in various engine combustion modes. We studied Euro 6 E10 reactivity with EGR additions of 20 % and 40 % (by mass) doped, in select cases, with high levels of NOx (874, 1501, 3174, and 5568 ppm, by mol%). Experiments were performed in two high-pressure shock tubes (HPSTs) and two rapid compression machines (RCMs) over a wide range of temperature (658–1610 K), equivalence ratio (0.5, 1.0) and at pressures of 20 and 30 bar. Results show that EGR addition inhibits Euro 6 E10 gasoline reactivity in the intermediate- and low-temperature regimes, while it is minimally affected at high-temperatures. In contrast, a strong reactivity-promoting effect of NOx is observed at temperatures greater than 825 K for all equivalence ratios investigated, while an inhibiting effect is seen at lower temperatures with a high doping of NOx (1501 ppm). For fuel-lean cases, where Euro 6/EGR mixtures are sensitized with 3174 – 5568 ppm NOx, a significant reactivity-promoting effect is observed across the entire range of conditions investigated, except at temperatures below 830 K, where the NOx-inhibiting effect dominates. A gasoline surrogate model is developed by combining a detailed gasoline surrogate mechanism with appropriate sub-models and making minor updates. The proposed model captures well the influence of EGR and EGR/NOx on Euro 6 E10 autoignition over the wide range of conditions studied here. Finally, sensitivity analyses were conducted to identify key reactions contributing to the perturbative effects of EGR and EGR/NOx on oxygenated gasoline ignition.

Effects of intake conditions on a dual-fuel spark-assisted compression ignition engine with polyoxymethylene dimethyl ether and methanol as fuels

Dual-fuel spark-assisted compression ignition (DF-SACI) is an advanced engine combustion mode. The use of polyoxymethylene dimethyl ether (PODE) and methanol as fuel can reduce the carbon emissions of the DF-SACI engine. To improve the combustion continuity and minimize the knocking and emissions of DF-SACI engines, the effects of intake heating and boosting were investigated. The results showed that the combination of intake heating and delayed spark ignition promoted fuel diffusion and prevented multi-peak heat release. Intake boosting promoted the transformation of compression ignition into flame propagation ignition. Intake heating and boosting allowed engine combustion optimization. The brake thermal efficiency was 41.4 % and 44 % when the brake mean effective pressure was 0.6 and 0.8 MPa, respectively, and the maximum pressure rise rate, coefficient of cyclic variation in the indicated mean effective pressure, and emissions were within reasonable ranges. A high intake air temperature combined with delayed spark ignition reduced the enrichment of PODE, thereby reducing the self-ignition probability of the fuel mixture, which can reduce knocking. When intake boosting was applied, the adoption of an excess air coefficient (λ) of 1.8 eliminated knocking under most conditions. Intake heating improved fuel reactivity and increased the ratio of compression ignition, to allow for the simultaneous reduction of hydrocarbon (HC) and NOx emissions. The effects of intake boosting on NOx and HC emissions were related to the energy ratio of PODE. As the energy ratio of PODE is between 47 % and 68 %, the appropriate increase in λ reduced both HC and NOx emissions. The results are conducive to the development of low-carbon engines and can provide a new direction for engine research.

Characterization of in-cylinder spatiotemporal flame and solid particle emissions for ethanol-gasoline blended in gasoline direct injection engines

Stricter regulations for internal combustion engines have necessitated the inclusion of eco-friendly fuels with conventional ones to reduce gas and solid emissions. Gasoline direct injection (GDI) engines, however, have been found to produce more particle number and mass emissions than port fuel injection engines. To address this, bioethanol fuel has been selected as an additive eco-friendly fuel for gasoline, with the aim of reducing particle emissions. In this study, we quantitatively characterize in-cylinder spatiotemporal flame to feature combustion performance and particle emissions for ethanol fuel in the GDI combustion chamber. We examined three engine combustion modes differed in equivalence ratio and injection strategy to produce various combustion results to quantify combustion performance and particle emission characteristics. Using an eight-channel non-intrusive flame luminosity sensor in one cylinder, we measured the flame front and its propagation direction. At the tailpipe, we measured particulate emissions using an engine exhaust particle sizer and a micro soot sensor coupled with a catalytic stripper that removed semi-volatile compounds. Our study found that increasing ethanol fuel content for different combustion modes resulted in distinct combustion and flame development. The particle size distribution also showed different patterns at each combustion mode, depending on the ethanol content. Lean combustion modes yielded high diffusion flame intensity compared to stoichiometric combustion mode, which resulted in a larger amount of particle formation. The physical properties of ethanol fuel were found to predominantly determine the fuel-air mixture quality, combustion process, and flame development at each combustion mode. An increase in ethanol fuel content at lean-homogeneous mode resulted in higher diffusion flame intensity and larger particle emissions. Our comparative study of flame and solid particles for ethanol fuel content improves the understanding of in-cylinder combustion processes and their correlations.

Development of a reduced oxidation mechanism with low-temperature chemistry for real biodiesel methyl esters

Accompanied with the development of advanced engine combustion modes, biodiesel as an important biorenewable fuel has the potential to be a regular engine fuel due to its advantages in carbon neutrality and reducing the emission of major pollutants. In the present study, a compact biodiesel oxidation mechanism for the numerical study of low-temperature biodiesel combustion is developed by reducing a comprehensive mechanism based on five major biodiesel methyl esters. For the mechanism reduction, a method based on direct and indirect species interactions is developed and proven to have improved effectiveness in reducing large complex mechanisms compared to existing methods. The method is preceded by reaction path analysis and followed by isomer lumping and sensitivity analysis, and the overall reduction process finally leads to a compact biodiesel mechanism with 187 species and 689 reactions. The fidelity of the reduced biodiesel mechanism is first demonstrated by simulating the auto-ignition of homogeneous biodiesel-air mixtures from various initial conditions. Predicted ignition delay data show discrepancies in the order of milliseconds, compared to those predicted using the original mechanism and experimental data. Agreement is also found in the instantaneous mole fraction of major species and mixture temperature, indicating that the reduced mechanism preserves the key reaction paths of the original mechanism. A further validation of the reduced mechanism is also accomplished by simulating the low-temperature oxidation of saturated and unsaturated biodiesel methyl esters in a jet-stirred reactor, and reasonable agreement is observed between predicted mole fraction of major product species and the corresponding experimental data at different temperatures.

Technological and environmental advantages of a new engine combustion mode: Dual Biofuel Intelligent Charge Compression Ignition

With the rapid development of the world economy, the demand for energy will inevitably increase the resource shortage and environmental pollution problems. Therefore, the coordinated development of energy and environment is an important way to achieve the United Nations (UN) Sustainable Development Goals (SDGs). Here, the dual biofuel intelligent charge compression ignition (ICCI) mode fuelled with butanol and biodiesel was demonstrated to achieve a high-efficiency and ultra-low emissions, which will have global real-world energy influence. The maximum thermal efficiency of the butanol/biodiesel ICCI mode is 3.5% higher than the absolute efficiency of the conventional mode, and the nitrogen oxide emissions decreased by 76.69% to 99.47%. The butanol/biodiesel ICCI mode has the potential to achieve carbon neutrality in the road transport sector and mitigate the greenhouse effect. Hence, direct air pollutants would be eliminated. Meanwhile, with the increasing production of biofuels worldwide, this work not only improves the environmental pollution and relieves the energy crisis, but also provides a method to deal with the mutual restraint between energy, environmental and technology.

Assessment of performance, combustion and emissions characteristics of methanol-diesel dual-fuel compression ignition engine: A review

The energy security concern and rapidly diminishing fossil fuel resources demand the development of renewable and economically attractive fuel for reciprocating engines. Methanol is a promising renewable alternative fuel. Numerous studies have been carried out to explore the various aspects of the utilization of methanol in compression ignition (CI) engine. This review paper presents a detailed analysis of the effect of methanol on performance, combustion, and emission (NOx, CO, HC, and soot) characteristics of conventional CI-engine along with dual-fuel combustion mode. This study focuses on methanol utilization in dual-fuel mode, which is an advanced engine combustion mode. First, methanol production and solubility issues of methanol in diesel are briefly discussed. This study discusses the soot and nano-particle emission from the methanol fueled CI-engine, which is one of the main concerns in the current emission legislation. It was found that the utilization of methanol in CI-engine has the potential to improve the performance and simultaneously with a significant reduction in NOx, CO, soot, and nano-particle emissions in comparison to neat diesel operation. However, unburnt HC emission reduces for methanol-diesel blended fuel operation whereas HC emissions are higher for methanol-diesel dual-fuel operation.

A reduced mechanism for the combustion of gasoline-ethanol blend on advanced engine combustion modes

A reduced mechanism composed of 144 species and 653 reactions is developed in the present study for simulating the combustion and soot emission of gasoline-ethanol blends on advanced engine combustion modes. The sub mechanism for gasoline combustion is reduced from a detailed mechanism based on the surrogate mixture of n-heptane, iso-octane, toluene, and 1-hexene. A composite approach composed of the path flux analysis and sensitivity analysis is used to perform the reduction. The reduced gasoline mechanism is comprehensively validated against the original detailed mechanism by predicting ignition day, instantaneous temperature, and species mole fraction during the homogeneous auto-ignition and the temperature profiles of perfectly stirred reactor, especially under low-temperature combustion conditions. A reduced ethanol mechanism is also obtained using the same reduction approach and then combined with the reduced gasoline mechanism. By further implementing elementary reactions related to the formation of polycyclic aromatic hydrocarbons (PAHs), the resulting combined mechanism can be used to simulate the ignition, combustion, and PAHs formation of gasoline-ethanol blends with different ratios. The fidelity of the present combined mechanism is comprehensively examined by predicting ignition delay, laminar burning velocity, and PAHs formation of various blends of gasoline surrogates and ethanol. Good agreement is obtained between the predicted properties and the corresponding experimental data.

The impact of hybridization, engine combustion method, and energy management system connectivity on heavy-duty vehicle operation

A wide range of strategies for reducing energy consumption from heavy-duty vehicles have been explored from vehicle electrification to real-time vehicle energy management based on vehicle-to-vehicle and vehicle-to-infrastructure communication. Full electrification of heavy-duty vehicles can be challenging due to current limitations on battery energy density. However, hybridization and the implementation of high efficiency engines present other potential near-term solutions. In contrast to many prior studies that have explored the use of one or two of these techniques, this work discusses the combined influence of hybridization level, engine combustion mode, and connected energy management on fuel efficiency in heavy-duty applications. The impact of hybridization in different driving conditions is quantified and the effectiveness of hybrid powertrain structures with different engine combustion strategies is also explored. Utilizing an alternative combustion strategy can improve fuel efficiency by 5% in conventional and mild hybrids but was found to have a more minimal impact in full hybrids. An additional layer of complexity is also introduced when vehicles have some degree of connectivity and this influence on the energy management method is investigated by comparing control approaches which leverage current and future vehicle speed information. Connectivity and the ability to optimize energy production in real-time was found to be essential in uncertain cases and enable improvements in fuel consumption of up to 12% over baseline cases.

Gas-phase autoignition of diesel/gasoline blends over wide temperature and pressure in heated shock tube and rapid compression machine

Diesel/gasoline blended fuel, also named as dieseline, has attracted worldwide interests in varied advanced engine combustion modes dominated by mixing time scale and chemical reaction time scale. However, the research on ignition properties and chemical reaction mechanism of diesel/gasoline blends over wide operating conditions is still lacking. In current study, ignition delay time measurement of diesel/gasoline blends with different diesel proportion (30%, 50%, and 70% by volume) were conducted in a heated shock tube and a heated rapid compression machine (RCM) covering a broad range of temperatures between 636 and 1317 K at pressures between 6 and 20 bar for gas-phase dieseline/O2/N2 mixture at varying equivalence ratios from 0.5 to 1.5. The experimental results revealed different dependence of ignition delay time on pressure, equivalence ratio and composition at different temperatures and varying negative-coefficient (NTC) behaviors were also observed at intermediate-temperature regime. The increase in proportion of diesel led to shorter ignition delay times under all conditions, though the ignition data at high temperature only showed marginal discrepancies. Besides, a crossover of ignition data occurred at the highest temperature for varying equivalence ratios. A tertiary surrogate for diesel and a tertiary surrogate for gasoline were chosen to calculate conditions after reflected shock in shock tube and compression in RCM. Then, simulations of ignition delay time for diesel/gasoline blends were conducted using a detailed model. Finally, kinetic analyses were performed to gain insight into the ignition characteristic of diesel/gasoline blends.

Chemical/Physical Features of Particles Emitted from a Modern Automotive Dual-Fuel Methane–Diesel Engine

The dual-fuel (DF) diesel–natural gas (NG) combustion concept for automotive engine applications has received increased attention in the recent years. The reasons of such interest lie in the need to identify energy sources alternative to fossil oil fuels, valid and competitive from an environmental point of view. Gaseous fuels, such as NG and methane, are very promising and highly attractive to this aim because of their easy availability, widespread distribution infrastructure, low cost, and clean-burning qualities. With respect to conventional diesel fuel, in fact, NG and methane permit a significant reduction of CO2 and are less prone to soot formation. Notwithstanding that the significant soot reduction offered by the DF engine combustion mode is a consolidated result, the compliance with future stringent regulations on engine particulate emissions will still require the adoption of after-treatment devices, such as the diesel particulate filter (DPF). Therefore, a complete characterization of the parti...

Hydrocarbon impact on NO to NO2 conversion in a compression ignition engine under low-temperature combustion

Compression ignition engines can employ high rates of exhaust gas recirculation to realize low-temperature combustion in order to reduce the NOx emissions. However, a substantial increase in NO2 contribution to the NOx emissions is also observed. The relationship between this NO to NO2 conversion is also affected by the hydrocarbons originating mainly from the fuel. This can have important consequences for the design of the exhaust after-treatment system. Therefore, this article presents an empirical investigation of the impact of hydrocarbon emissions on the in-cylinder NO–NO2 conversion process. First, engine motoring tests are performed with propane and NO gases dosed into the engine intake manifold. Engines with different compression ratios are employed to study the effect of in-cylinder temperature and intake HC–NO ratio on the NO–NO2 conversion process. Next, the hydrocarbon impact on the NOx survivability at different engine combustion modes is investigated using a common-rail diesel engine test platform with independent control of exhaust gas recirculation, intake boost, and exhaust back pressure. Results show that the existence of hydrocarbon has a strong promotion effect of converting NO to NO2. During compression test, NO–NO2 conversion rate can reach 95% under certain intake HC–NO concentration ratio, and the minimum HC–NO concentration ratio to sustain a high NO–NO2 conversion rate is sensitive to peak in-cylinder temperature; engine combustion results also show that hydrocarbon not only can promote the in-cylinder NO–NO2 conversion process, but also has the potential of decreasing the total NOx emissions under low-temperature combustion mode.

Simulation and experiments of advanced gasoline engine combustion modes from spark ignition to compression ignition

Simulation and experiments of advanced gasoline engine combustion modes from spark ignition to compression ignition

Simulation and experiments of advanced gasoline engine combustion modes from spark ignition to compression ignition

This paper reviews some advanced gasoline engine combustion modes, including direct injection spark ignition (DISI), homogeneous charge compression ignition (HCCI), stratified charge compression ignition (SCCI), and multiple premixed compression ignition (MPCI). To reveal the engine knock mechanism of DISI combustion, the flame propagation and pressure oscillation in a boosted gasoline engine were numerically analysed. To further improve thermal efficiency and reduce emissions, the effects of injection strategies on fuel economy, emissions, and heat release in HCCI combustion were studied. To solve the challenges of ignition control and rapid combustion of HCCI, SCCI and MPCI combustion modes were adopted to achieve high efficiency, low emissions, and low acoustic noise simultaneously.

Experimental study on partially premixed compression ignition combustion fueled with a low octane number primary reference fuel using two-stage fuel supplying

An experimental study of partially premixed compression ignition combustion with low octane fuel was conducted on a single-cylinder engine. The effects of the external exhaust gas recirculation and intake boost on this partially premixed compression ignition combustion and emissions were investigated. During the experiments, a trade-off relationship between the NOx and smoke emissions was observed in this partially premixed compression ignition combustion. However, heavy exhaust gas recirculation usage has the potential to decrease NOx and soot emissions simultaneously at the expense of the fuel economy. It is determined that at an increased intake port pressure, the maximum in-cylinder pressure increases, and the ignition timing of the high-temperature combustion is retarded. Also, the peak value of the low-temperature combustion is slightly depressed, the peak value of the high-temperature heat release decreases significantly, and the maximum value of the diffusing burn increases to some extent. Compared to natural aspirated condition, the partially premixed compression ignition combustion with intake boost has the capability of simultaneously reducing NOx and soot emissions to ultra-low levels, that is, the intake boost could be an important strategy for the combustion and emission improvement in this advanced engine combustion mode.

Fractionation of engine exhaust hydrocarbons using flame ionization detection with variable temperature sample conditioner

The flame ionization detector is a standard instrument for measuring total hydrocarbon concentration in engine exhaust. Engine combustion modes such as diesel low-temperature combustion are known to produce higher levels of total hydrocarbon than conventional combustion modes, and a need exists to estimate species that may nucleate into nanoparticles upon dilution in the atmosphere. Exhaust hydrocarbon fractionation is useful for gaining better understanding about engine combustion and for developing aftertreatment catalysts for reducing emissions. Methods capable of measuring individual hydrocarbon species such as gas chromatography and Fourier transform infrared spectrometry do not measure the full range of species present in engine exhaust and are expensive. In this work, a custom-designed variable temperature sample conditioner was developed for use with two fast-response flame ionization detectors to fractionate the hydrocarbons present in engine exhaust as a function of component volatility. A condensation model for fuel alkanes was also developed to be used in concert with the experimental data to determine the fraction of fuel-like hydrocarbons within the total hydrocarbon measurement. Our results indicate that the variable temperature flame ionization detector method yields similar unburned hydrocarbon fraction to reported literature values using more extensive speciation studies at similar engine conditions. We find that while low-temperature combustion engine operation emits higher concentrations of total hydrocarbon than conventional combustion modes, the fraction of less volatile hydrocarbon species is higher for lower engine load, regardless of the combustion mode.

Mixing and flame structures inferred from OH-PLIF for conventional and low-temperature diesel engine combustion

The structure of first- and second-stage combustion is investigated in a heavy-duty, single-cylinder optical engine using chemiluminescence imaging, Mie-scatter imaging of liquid-fuel, and OH planar laser-induced fluorescence (OH-PLIF) along with calculations of fluorescence quenching. Three different diesel combustion modes are studied: conventional non-diluted high-temperature combustion (HTC) with either (1) short or (2) long ignition delay, and (3) highly diluted low-temperature combustion (LTC) with early fuel injection. For the short ignition delay HTC condition, the OH fluorescence images show that second-stage combustion occurs mainly on the fuel jet periphery in a thickness of about 1 mm. For the long ignition delay HTC condition, the second-stage combustion zone on the jet periphery is thicker (5–6 mm). For the early-injection LTC condition, the second-stage combustion is even thicker (20–25 mm) and occurs only in the down-stream regions of the jet. The relationship between OH concentration and OH-PLIF intensity over a range of equivalence ratios is estimated from quenching calculations using collider species concentrations predicted by chemical kinetics simulations of combustion. The calculations show that both OH concentration and OH-PLIF intensity peak near stoichiometric mixtures and fall by an order of magnitude or more for equivalence ratios less than 0.2–0.4 and greater than 1.4–1.6. Using the OH fluorescence quenching predictions together with OH-PLIF images, quantitative boundaries for mixing are established for the three engine combustion modes.

Effects of Key Factors on the Engine Combustion Mode Switching Between HCCI and SI

A technical strategy for a rapid and smooth switching between spark ignition (SI) mode and homogeneous charge compression ignition (HCCI) mode on a gasoline direct injection engine has been proposed and investigated, which involves an electrohydraulic two-stage cam profile mechanism and special injection strategies. The key factors that affect the HCCI/SI mode switching processes were analyzed on the basis of transient engine tests in terms of combustion parameters and exhaust emissions. It is shown that special care should be taken on the engine functionalities during the mode switching from SI to HCCI, which appears to be more difficult, and simultaneous control of the key parameters such as injection mass, injection timing, and spark timing is required. Various strategies and their general criteria for the mode switching were discussed. An optimized combination of selected control strategies has been demonstrated with a satisfactory switching process completed in ten engine cycles, without any abnormal combustion cycles in between.