Low Temperature Combustion Engine Research Articles

Machine learning approaches for identification of heat release shapes in a low temperature combustion engine for control applications

This paper presents the application of machine learning classification algorithms to identify and classify different heat release rate (HRR) shapes to control the combustion for an optimal multi-mode low-temperature combustion (LTC) engine operation. Low-temperature combustion engine produces low nitrogen oxides (NOx) and soot emissions and offers high thermal efficiency. But high in-cylinder pressure rise rates limit the operating range of the LTC engine. Therefore, it is imperative to control combustion in the LTC engine for safe operation. To this end, the HRR traces for over six hundred engine operating conditions are classified using supervised (i.e., Decision Tree, K-Nearest Neighbors (KNN), and Support Vector Machines (SVM)) and unsupervised (i.e., Kmeans clustering) machine learning approaches to segregate different combustion regimes based on HRR shape. Kmeans clustering was not successful in classifying the HRR shapes. Among different supervised machine learning techniques, SVM has proved to be the best method, having an overall classifier prediction accuracy of 92.4% for identifying the distinct shapes using normalized HRR data. In addition, three classifiers have been trained based on the combustion parameters and control inputs. These classifiers are then used as scheduling variables to develop predictive models. A model predictive control (MPC) framework is developed to control multi-mode LTC engine on cycle-to-cycle basis. The MPC framework achieved the simultaneous reference tracking of combustion phasing (CA50) and indicated mean effective pressure (IMEP) while constraining maximum pressure rise rate (MPRR) below 8 bar/CAD.

Fuel control strategy for robust low-load gasoline low temperature combustion

To achieve robust low-load LTC (Low Temperature combustion), precise metering of fuel is required since the combustion is very sensitive to the variation of the injected fuel quantity, which could range from 1 to 3 mg per injection pulse. Open-loop calibration of individual injectors is simply not a practical option and therefore a fuel control strategy has been developed to ensure robust low-load LTC combustion and validated through experiments on a 2.2 L 4-cylinder LTC engine at two different coolant temperatures. The results show that the fuel control strategy significantly improves low-load LTC combustion stability by reducing cylinder-to-cylinder variation in delivered fuel masses due to different injector characteristics even when engine operating conditions are changed.

Injection strategy of methanol for high loads and low NOx emissions in a neat methanol LTC engine

Methanol is a low carbon and clean burning renewable fuel. Though low temperature combustion (LTC) of neat methanol results in almost no smoke with ultra-low NOx, the extremely low cetane number poses challenges. This experimental study demonstrates LTC of neat methanol at full load by combining direct and port injection of this fuel with controlled intake air temperature (IAT). The effects of important variables including IAT and port (premixed) and direct-injected methanol shares on combustion, performance, regulated and unregulated emissions were investigated. The timing of the direct-injected methanol had to be retarded with an increase in the premixed methanol share and IAT in order to limit the pressure rise rate without affecting the ITE. At high IATs, the premixed methanol burned first, followed by the directly injected methanol, at low IATs, these phases merged, resulting in a high rate of heat release. Employing the lowest possible IAT and the highest possible premixed methanol share led to high ITE. Increase in the MDIP to 450 bar was advantageous due to better fuel evaporation and enhanced combustion. Negligible smoke, very low NOx of 2.7 g/kWh, high ITE of 45% and unburned HC and methanol emissions lesser than 3 g/kWh could be achieved.

Experimental study of triple fuel physiognomies on LDRCCI diesel engine combustion

Environmental deterioration and the current energy crisis are the driving factors for better combustion technologies and renewable, clean energy sources. To improve engine combustion efficiency and reduce emissions, numerous low-temperature combustion techniques have been investigated. Among all low-temperature combustion engines, the reactivity-control compression ignition (RCCI) engine is the most recent and preferred one to reduce PM and NOx emissions to govern the ignition and combustion processes. However, it has not yet revealed the optimal solutions. The port injection is used for the secondary fuel system to manage emissions, in-cylinder charge reactivity, and combustion phasing during RCCI operation. A triple-fuel RCCI engine that burns a port-injected blend and direct-injected diesel fuel has been experimentally investigated in this work. The G5E15-RCCI engine was observed to run at a maximum cylinder pressure and HRR of 90.76 bar, and 63.02J/deg respectively at 3000 rpm while for the baseline fuel they are much lower at 58.69 bar and 11.8J/deg respectively with the speed being 2500 rpm. The NOx and CO2 emissions were at their lowest levels with the engine running on G5E15, whereas they were at their highest for the engine running on baseline mode. Under G5E15-RCCI engine operation, CO and UHC increase as usual while G10E10-RCCI emits a minimum that can be taken as a novel finding in which CO and HC emission reduction was demonstrated with RCCI in this study. The brake power in all experiment cases was observed as approximately the same with slight increases for G10E10 at speeds greater than 2400 rpm. The maximum engine brake torque occurred in the speed range of 2000-2600 rpm for G10E10 and in the narrower range of 2200- 2400 rpm for the G5E15 port-injected blend. Better brake thermal efficiency was noted for the engine running on baseline fuel in the speed range of 2200-2600 rpm while being higher for the engine running on G5E15 RCCI mode at 2800 and 3000 rpm as such.

Unconventional gasoline spray injection events: Compared evolution of experimental data and numerical simulations

The current homologation standards in the automotive field impose the manufacturers to develop very efficient and clean engines. Low-Temperature Combustion engines have the potential to simultaneously reduce all the pollutants released while maintaining high efficiency. Among them, in Gasoline Compression Ignition (GCI) combustion technology, multiple injections allow to generate a tailored stratified charge which can auto ignite limiting the rough Pressure Rise Rate (PRR) and heat release rate typical of GCI. Therefore, the three-dimensional local distribution of the mixture becomes the key-point which the engine performance depends on. Due to emphasis on the multi-dimensional and local nature of the mixture formation phenomenon, three-dimensional CFD simulations are a promising and attractive method aiming at the design of the injection event features (timing, pattern, etc.). This paper deals with both experimental and CFD campaign on the evolution of a gasoline spray at ultra high-pressure multiple injection as well as high backpressure, typical of Gasoline Compression Ignition engines. The experimental tests have been conducted on a reference Diesel Common-Rail injector which shots in a constant-volume chamber. The hydraulic behaviour of the injector was characterized by means of the Bosch Tube principle whilst the Mie-scattering technique was used to capture the spray images. The numerical methodology is required to predict the Liquid Length Penetration and the jet morphology features (shape, area). Both experiments and simulations were conducted at different values of injection pressure (350, 500, 700 bar), back pressure (1–8 bar), energizing time (350, 600 µs), according to the operations of a real reference GCI test engine. Furthermore, a dedicated sub-model which takes into consideration the effect of the spray dynamics during the injection transient opening stage has been validated. The importance of this approach when dealing with short energizing time (e.g. 350 μs) is shown.Comparing both the experimental and numerical results, the model has proven to efficiently reproduce the spray penetration and morphology features, also under the hypothesis of injector ballistic phase operations, whose determination is crucial in the early development and sustainability of such combustion concept.

Experimental and kinetic modeling study of low-temperature oxidation of n-pentane

Attractiveness in advanced low-temperature combustion engines drives a constantly updated understanding of low-temperature oxidation chemistry. In this work, the low-temperature oxidation chemistry of n-pentane in two jet-stirred reactors at atmospheric pressure and in the temperature range of 500–825 K was investigated using combined analysis methods of synchrotron vacuum ultraviolet photoionization mass spectrometry, gas chromatography, and Fourier transform infrared spectroscopy. Furthermore, the gaseous mixture from JSR was collected in acetonitrile for subsequent product characterization using flow injection analysis, high-pressure and ultra-high-pressure liquid chromatography coupled to a Thermo Scientific™ Orbitrap® Q-Exactive high-resolution mass spectrometry. Numerous intermediate species were identified by these analytical methods, which contributed to unraveling the low-temperature oxidation reaction network of n-pentane. A detailed n-pentane model was tentatively developed to reduce deviations between experimental measurements and model predictions by updating the rate constants of C5 keto-hydroperoxide decomposition, C5 hydroperoxy cyclic ether decomposition, and Korcek reactions of C5 keto-hydroperoxide, and by introducing pressure-dependent rate constants for the reaction classes of Q˙OOH + O2, Q˙OOH decompositions, concerted HȮ2-elimination of RȮ2, C5 keto-hydroperoxide decomposition, C5 hydroperoxy cyclic ether decomposition, and Korcek reactions of C5 keto-hydroperoxide, and by adding more detailed sub-mechanisms for C5 cyclic ethers and C5 keto-hydroperoxides. This updated model was validated against a set of available experimental data, including jet-stirred reactor species data and ignition delay times. These exploratory updates of the kinetic model reveal the considerable influence of the rate constants of hydroperoxide decomposition and the pressure-dependent rate constants of key reaction classes on the kinetic model predictions, highlighting the future demands for high-precision quantum chemistry calculations of the pressure-dependent rate constants of the aforementioned reaction classes to reduce mechanism uncertainties and to develop accurate and robust chemical kinetic models.

Additive-Mixing Fuel Injection (AMFI): A device for robust control and improved performance of high-efficiency LTGC engines

Low-temperature gasoline combustion (LTGC) engines can provide high efficiencies with very low NOx and particulate emissions. Despite these major advantages, methods for controlling LTGC combustion timing, achieving robust autoignition, and good low-load performance have challenged the development of practical LTGC engines. A key reason is that the ideal reactivity of the fuel varies with operating conditions, with low-reactivity fuels working well at high loads and higher-reactivity fuels working better at low loads. This article introduces a new technique called Additive Mixing Fuel Injection (AMFI) that adjusts the reactivity of the gasoline to obtain good performance over the operating map. Moreover, AMFI can provide robust combustion-timing control because it precisely meters very small amounts (0.01–0.6 mm3) of an ignition-enhancing additive into the fuel each engine cycle. The additive used was 2-ethylhexyl nitrate (EHN), a common, inexpensive diesel-fuel ignition improver, but other additives could be used. Because additive amounts are so small, a 2-gal reservoir would be sufficient for medium-duty applications with refilling only at service intervals of about 8000 mi. The AMFI system has been installed on a single-cylinder LTGC research engine and demonstrated to provide robust combustion-timing control over wide ranges of combustion phasing, fueling rate, intake boost, engine speed, and intake temperature. AMFI also increases the fuel’s reactivity sufficiently to greatly reduce or eliminate the need for charge heating, simplifying engine design and significantly increasing thermal efficiency and the maximum load at low-boost conditions. The nitrogen in the EHN produced a modest increase in NOx, but it was mitigated by lower intake temperatures, and NOx emissions remained very low. Finally, the additive increases the sensitivity of autoignition reactions to variations in the local fuel/air mixture within the charge. This allows the use of controlled fuel stratification for improved LTGC-engine performance, and its potential to improve low-load operation was demonstrated.

Performance of octane index in LTGC engines from beyond MON to beyond RON

This work analyzes the inability of the Octane Index (OI) to characterize the autoignition resistance of gasoline-like fuels in a Low-Temperature Gasoline Combustion (LTGC) engine. Experimental studies in the Sandia LTGC engine at naturally aspirated ‘beyond-MON’ and high-boost ‘beyond-RON’ conditions showed a poor correlation between OI and autoignition reactivity. These experiments were successfully replicated in CHEMKIN, allowing detailed studies of the factors affecting the OI correlation. Systematic investigations were conducted to determine why the OI performs less well for LTGC combustion compared to end-gas autoignition (i.e. knock) in spark-ignition (SI) engines. A pseudo-MON condition that follows the pressure–temperature (P-T) trajectory of the real MON test was tested numerically, using 10 different fuels, leading to the conclusion that the OI correlation performs very well for an SI engine running at close-to-MON conditions. The effects of each difference between SI and LTGC combustion were then analyzed for four P-T trajectories: ‘beyond-MON’, ‘MON test’, ‘between RON-MON’, and ‘beyond-RON’ conditions. These differences included changes in: equivalence ratio, engine speed, and residence-time history along the P-T trajectory for piston-only compression, as used for LTGC, compared to compression by the piston plus flame propagation for SI combustion. For LTGC combustion, the OI correlation did not characterize the autoignition quality of gasoline-like fuels well for any P-T trajectory, but the factors causing this poor performance varied with conditions. For example, at naturally aspirated LTGC conditions (beyond-MON), changes in equivalence ratio were the primary cause, followed by differences in the P-T trajectory and changes in residence time. Whereas, for intake-boosted beyond-RON conditions, differences in the P-T trajectory had the largest effect, followed by changes in residence time. Finally, the parameter K that characterizes the OI correlation showed values that contradict the OI theory under realistic LTGC conditions, suggesting that K might be meaningless for LTGC engines.

RESEARCH ON NUMERICAL SIMULATION OF PCCI ENGINE: A REVIEW

The global environment is being affected by the use of fossil fuels to provide energy for internal combustion engines (ICE) due to a large amount of CO2 emission. Specific toxic substances are NOx, and CO, soot, particulate matter that exists in the environment at high densities while having a global impact. The automotive industry of countries worldwide is constantly changing and evolving to discover new solutions that reduce fuel use while developing cleaner and more advanced combustion methods, which as a low-temperature combustion engine (LTC). This study uses computational fluid dynamics (CFD) to understand partial pre-mixed compression combustion (PPCI), with HCCI and RCCI being advanced low-temperature combustion concepts. Lowering the average combustion temperature is an advantage of PCCI; it optimizes CO and NOx emission rates while maintaining high thermal efficiency. Investigate the intake pattern, including flame length, mixing pulse, and intake air volume, to determine the importance of that factor for oxidation using the LES. Studies have been performed using RANS and LES models to stimulate mixing and combustion.

Study on cool flame radical index and oxygen concentration dependence of oxygenated fuels

The growing utilization of alternative fuels has sparked an interest in understanding the combustion characteristics of oxygenated fuels at low temperature. Cool flame extinction limits provide direct measures of the low-temperature reactivity of fuels and critical information for advanced low-temperature combustion engine design. This paper investigates the effects of fuel and oxygen concentrations on the extinction limits of diffusion cool flames for oxygenated fuels, including dimethyl ether, methyl decanoate, and 1-dodecanol in an atmospheric counterflow burner. The cool flame radical indexes of these oxygenated fuels are developed by isolating the thermal and transport effects from the chemical contribution to diffusion cool flame extinction. The results show that the ranking of low-temperature reactivities of long carbon chain oxygenated fuels, compared with n-alkane, is ether > n-alkane > alcohol > ester for a similar carbon number. Furthermore, due to the critical role of multiple oxygen addition reactions in the low-temperature chemistry, the relationship between the cool flame extinction limit and the oxygen concentration is also explored. The results show that the cool flame extinction limits of the oxygenated fuels are proportional to a nth power of the oxygen concentration, [O2]n, due to the combined effects of multiple oxygen addition reactions and the negative temperature coefficient in low-temperature chemistry. Additionally, the measured n number of 1-dodecanol is found to be larger than 2, which suggests the existence of the third oxygen addition reactions in low-temperature chemistry for large alcohols.

Replicating HCCI-like autoignition behavior: What gasoline surrogate fidelity is needed?

This work seeks to characterize the fidelity needed in a gasoline surrogate with the intent to replicate the complex autoignition behavior exhibited within advanced combustion engines, and specifically Homogeneous Charge Compression Ignition (HCCI). A low-temperature gasoline combustion (LGTC) engine operating in HCCI mode and a rapid compression machine (RCM) are utilized to experimentally quantify fuel reactivity, through autoignition and preliminary heat release characteristics. Fuels considered include a research grade E10 U.S. gasoline (RD5-87), three multi-component surrogates (PACE-1, PACE-8, PACE-20), and a binary surrogate (PRF88.4). Each fuel was studied at lean/HCCI-like conditions covering a wide range of temperatures and pressures that are representative of naturally aspirated to high boost engine operation. Detailed chemical kinetic modeling is also undertaken using a recently updated gasoline surrogate kinetic model to simulate the RCM experiments and to provide chemical insight into surrogate-to-surrogate differences.The LGTC engine experiments demonstrate nearly identical reactivity between PACE-20 and RD5-87 across studied conditions, while faster phasing is seen for both PACE-1 and PACE-8 due to their stronger intermediate- and low-temperature heat release (ITHR/LTHR) at naturally aspirated and boosted conditions, respectively. The RCM experiments reveal typical low-temperature, negative temperature coefficient (NTC) and intermediate-temperature autoignition behaviors at all pressure conditions for RD5-87, which are qualitatively reproduced by all surrogates. Quantitative discrepancies in both autoignition and preliminary heat release are observed for all surrogates, while their ability to replicate RD5-87 autoignition behavior follows the order of PACE-20 > PACE-1 > PACE-8 > PRF88.4. Excellent mapping is obtained between the LGTC engine and the RCM, where the engine pressure-time trajectories can be characterized by the regimes represented by the RCM autoignition isopleths. The kinetic model performs commendably when simulating both autoignition and preliminary heat release of PACE-20, while typically overpredicting ignition delay times for PACE-1, PACE-8 and PRF88.4 at high-pressure and low-temperature/NTC conditions. Sensitivity and rate of production (ROP) analyses highlight surrogate-to-surrogate differences in the governing chemical kinetics where n-pentane initiates rapid OH branching at a faster rate and an earlier timing for PACE-20 than iso-pentane does for PACE-1 and PACE-8, making it computationally more reactive than the other surrogates. The current study highlights the need to include non-standardized properties, such as the lean/HCCI-like autoignition characteristics, in addition to ASTM properties (e.g., RON, MON) as metrics of fuel reactivity and targets to be matched when formulating high-fidelity surrogates that fully capture gasoline advanced combustion behavior such as HCCI-like autoignition.

Experimental investigation on the effect of EGR rate variation on emissions in optimized PCCI-DI diesel engine

Combustion in diesel engines is focusing towards unexplored combustion concepts where innovative combustion ideas are being developed following several engine control factors. Advanced low temperature combustion engines for automotive applications are one of the improvements in this regard. The test was conducted on a single cylinder, four stroke and air cooled diesel engine. The scope of this study is to investigate the impact of EGR rate variation (25%, 35% and 45 % EGR rates) on emission reductions in PCCI-DI diesel combustion approach showing a reduction of NOx–soot trade-offs than the conventional diesel combustion approach. The PCCI-DI diesel combustion in this setup is optimized applying the algorithm of grey relational analysis together with Taguchi method. This investigational setup used a methanol port injection and advanced injection timing for PCCI formation. Emission results from different EGR settings in the optimized PCCI-DI combustion scheme were analyzed and compared using surface and contour plots. From the experiment higher EGR rate resulted a decrease in NOx productions but an increase in HC, CO and smoke due to the combustion mode of the experimental setup. The study indicated that excess EGR application should be avoided to have an optimum PCCI-DI combustion having lower emission results.

Towards fossil-free fuels in sustainable powertrain; alcohol-fueled low-temperature combustion (LTC)

Low-temperature combustion (LTC) engines are able to reduce nitrogen oxides (NOx) and particulate matter (PM) emissions, simultaneously. LTC engines suffer from higher amounts of unburned hydrocarbon (uHC) and carbon monoxide (CO) emissions, particularly in low-load operating conditions of the engine. The existence of oxygen molecules in the alcohol fuels not only results in more combustion completeness but also leads to lower CO and uHC emissions.

Critical Review on Effects of Alcohols and Nanoadditives on Performance and Emission in Low-Temperature Combustion Engines: Advances and Perspectives

Critical Review on Effects of Alcohols and Nanoadditives on Performance and Emission in Low-Temperature Combustion Engines: Advances and Perspectives

Study on control-oriented emission predictions of PPCI diesel engine with two-stage fuel injection

Model predictive control (MPC) is an effective technology used to improve the control accuracy of low temperature combustion engines. The main purpose of this study is to establish a control-oriented emission prediction model based on fuel injection parameters, which provides the basis for the development of MPC controller for PPCI engines. In this study, the combustion model and backpropagation (BP) neural network emission prediction model of a partially premixed compression ignition (PPCI) diesel engine were established, through which the real-time combustion and emissions can be realized by inputting two-stage fuel injection parameters. The Wiebe function linearization method was proposed for the combustion model to achieve high-precision reconstruction of combustion at different fuel injection parameters. The nitrogen oxide (NOx) and particulate matter (PM) emissions were predicted using the combustion characteristics calculated by the combustion model. The results show that the established combustion model can accurately reconstruct the heat release rate and cylinder pressure of PPCI combustion, and the maximum error between the calculated and test values of the combustion parameters is less than 9%. The three-layer BP neural network can achieve high-precision predictions of NOx and PM emissions, with a prediction accuracy greater than 95%. Under the 300th continuous transient seconds, the cumulative prediction error of NOx was 2%, and the cumulative prediction error of PM was 4.9%, indicating high accuracy. This provides the basis for developing MPC controllers for PPCI engines.

Shock tube experimental studies on the ignition delay of n-heptane/ethanol fuel blends with acetaldehyde (CH3CHO) and oxynitride (NO/NO2) additives

In recent studies around low-temperature combustion (LTC) engines, it has been found that the incomplete oxidation products (IOP) within exhaust gas recirculation (EGR) presents non-negligible chemical effects. However, IOP generally has complex ingredients, and little literature available conducts quantitative and comparative studies on the effects of these ingredients. In this paper, CH3CHO, which is considerably abundant, and NO, which is most active, are selected as typical ingredients of IOP, and their effects on ignition delay times of n-heptane/ethanol fuel blends are studied experimentally in a shock tube covering the equivalence ratios of 0.5, 1, 1.5, temperature range of 900–1200 K, and pressure of 10 atm. Experimental results show that both CH3CHO and NO/NO2 (part of NO is inevitably converted to NO2) promote ignition, and the promoting effect of NO/NO2 is stronger than CH3CHO . It is consistent for both CH3CHO and NO/NO2 that the higher the concentration or, the lower the equivalence ratio, the greater the promoting effect. The difference is that the promoting effect of CH3CHO weakens with temperature increasing, while the promoting effect of NO/NO2 strengthens. Besides, the promoting effect of NO2 is weaker than that of NO, and NO2 even begins to inhibit ignition at temperatures below 960 K. In addition, it follows chemical kinetic analysis that both CH3CHO and NO/NO2 accelerate the decomposition of fuel by producing more OH radicals during the ignition stage. Although the additives are in trace amounts, the OH produced by their early involvement in reactions can effectively accelerate the ignition, which indicates the non-negligible chemical effects of IOP in EGR.

Thermo-kinetic multi-zone modelling of low temperature combustion engines

Many researchers believe multi-zone (MZ), chemical kinetics–based models are proven, essential toolchains for development of low-temperature combustion (LTC) engines. However, such models are specific to the research groups that developed them and are not widely available on a commercial nor open-source basis. Consequently, their governing assumptions vary, resulting in differences in autonomy, accuracy and simulation speed, all of which affect their applicability. Knowledge of the models´ individual characteristics is scattered over the research groups´ publications, making it extremely difficult to see the bigger picture. This combination of disparities and dispersed information hinders the engine research community that wants to harness the capability of multi-zone modelling.This work aims to overcome these hurdles. It is a comprehensive review of over 120 works directly related to MZ modelling of LTC extended with an insight to primary sources covering individual submodels. It covers 16 distinctive modelling approaches, three different combustion concepts and over 60 different fuel/kinetic mechanism combination. Over 38 identified applications ranging from fundamental-level studies to control development. The work aims to provide sufficient detail of individual model design choices to facilitate creation of improved, more open multi-zone toolchains and inspire new applications. It also provides a high-level vision of how multi-zone models can evolve.The review identifies a state-of-the-art multi-zone model as an onion-skin model with 10–15 zones; phenomenological heat and mass transfer submodels with predictive in-cylinder turbulence; and semi-detailed reaction kinetics encapsulating 53-199 species. Together with submodels for heat loss, fuel injection and gas exchange, this modelling approach predicts in-cylinder pressure within cycle-to-cycle variation for a handful of combustion concepts, from homogeneous/premixed charge to reactivity-controlled compression ignition (HCCI, PCCI, RCCI). Single-core simulation time is around 30 minutes for implementations focused on accuracy: there are direct time-reduction strategies for control applications. Major tasks include a fast and predictive means to determine in-cylinder fuel stratification, and extending applicability and predictivity by coupling with commercial one-dimensional engine-modelling toolchains. There is also significant room for simulation speed-up by incorporating techniques such as tabulated chemistry and employing new solving algorithms that reduce cost of jacobian construction.

Comparison of efficiency and emission characteristics in a direct-injection compression ignition engine fuelled with iso-octane and methanol under low temperature combustion conditions

Gasoline and methanol are highly recommended for low temperature combustion (LTC) engines due to their high research octane number. However, engines fuelled with these fuels suffer from high unburned hydrocarbon (UHC) and carbon monoxide (CO) emissions at low loads, which can be improved by controlling the level of mixture stratification. This paper reports on the experimental and numerical comparison of the emission characteristics and engine performance of methanol and iso-octane in a heavy-duty direct-injection compression ignition engine operating in HCCI and PPC regimes. Overall, methanol requires a higher intake temperature, compared with iso-octane, to counter the high heat of vaporization. The onset of ignition is from the relatively fuel-lean regions resulting in lower CO emissions. This is due to the methanol ignition delay times being less sensitive to the fuel/air mixture and the larger temperature gradient of the equivalence ratio. Methanol achieves lower charge stratification because of its low stoichiometric A/F ratio, which extends the SOI window with ultra-low NOx emissions. However, methanol suffers from higher UHC emissions in the HCCI regime due to fuel trapped in the crevice region. Three cases include HCCI, PPC with low and high mixture stratification were detailed investigated. Of these cases, PPC with low mixture stratification case shows the highest engine thermal efficiency and the lowest emissions. Methanol has more advantages operating in the PPC regime in the aspect of emissions.

A parametric modeling study of thermal barrier coatings in low-temperature combustion engines

• Low-temperature combustions are more favorable with the thick coating configurations. • In-cylinder thick thermal barrier coating improves the indicated thermal efficiency by 4.6%. • Thick thermal barrier coating increases the volumetric efficiency due to the lower IVC temperature. • Thick thermal barrier coating increases the exhaust enthalpy and reduces intake temperature requirement. In-cylinder thermal barrier coatings (TBCs) reduce heat transfer losses and increase thermal efficiency. It has been shown that thick TBCs negatively impact the performance of conventional combustion modes by degrading volumetric efficiency and increasing the propensity for end-gas knock. Low-temperature combustion (LTC) is an advanced combustion strategy that offers high efficiencies and low emissions. Due to the nature of kinetics-driven autoignition, LTC is fundamentally different from the conventional combustion modes, where the benefits and tradeoffs of thick TBCs need to be re-evaluated. Previous experimental studies showed the feasibility and the efficiency gains associated with a 2 mm thick TBC applied to the piston surface, as well as the reduction in the required intake temperature with no observable deterioration on the high load limit. However, the effects of TBCs and their independent thermophysical properties on LTC have not been systematically explored. It is necessary to perform a comprehensive study on the effects of TBC on LTCs from a fundamental thermodynamic perspective, which serves as the motivation for the current study. This study couples a 0D engine thermodynamic model to a 1D transient heat transfer model of the coating and piston. The model was first validated against the metal piston baseline, followed by validation against experimental data of the TBC cases at different engine loads. With confidence established in the model’s fidelity, three parameters are investigated independently: thermal conductivity ( k ), coating thickness, and volumetric heat capacity ( s ). The results revealed that the volumetric efficiency actually increases by 7.4 percentage points with a thicker coating due to a reduction in heat transfer during the compression stroke, which allows for a lower intake temperature requirement to reach autoignition. However, there is a thickness limit before the intake temperature becomes impractically low. The results show that elevating surface temperature is directly proportional to higher efficiency. Therefore, the optimal coating configuration for kinetically-controlled LTC is a combination of the lowest k , thickest coating before reaching the limit, and the lowest s , where the low k and high thickness contribute the most thermal efficiency gains (4.1 percentage points) and increased exhaust enthalpy (5.7%).

Energy management optimization for a power-split hybrid in a dual-mode RCCI-CDC engine

The electrification of propulsion systems in light passenger vehicles is essential to reach the objectives set by the different organizations that protect the environment. However, due to various aspects such as politician decisions, bad press, high powertrain production costs and a moderate reduction in energy consumption, purely electric vehicles are being a priority for several car manufacturers as well as for governments instead of hybrid vehicles. This article shows how hybrid electrification, using a low temperature combustion engine, is capable of reducing the energy consumption while drastically minimizing the particle matter (mainly soot) and NOx emissions, in a power split propulsion system. This is possible by means of a precise control of the operating conditions of the engine. To operate in the hybrid powertrain efficiently and with low emissions, several energy managements controller strategies are studied. In this work, adaptive Equivalent Minimization Control Strategy (ECMS) and Rule-Based Control (RBC) are used as online controller, and the dynamic programming optimal control is used to size the powertrain. In this sense, the electric machine maximum power, battery energy content, power split device gear ratio as well as the control parameter are studied. Both emissions and fuel consumption are included in the optimization function. The results show that it is possible to reduce the fuel consumption by 17.5% with an energy minimization-oriented strategy. In addition, ECMS is more effective to control both emissions and fuel economy. If a double target is applied, the fuel consumption is reduced to 5% while achieving Euro 6 emissions levels without the need for NOx and particulate matter aftertreatment systems. This strongly reduces the total cost of the propulsion system compared to a conventional vehicle, thus compensating the cost increase due to the hybridization without considering the fuel saving costs.