Low Temperature Combustion Engine Research Articles

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.

Performance and pollutant emission of the reforming-controlled compression ignition engine – Experimental study

The reforming-controlled compression ignition (RefCCI) is an innovative concept integrating the benefits of the low-temperature combustion engine and the High-Pressure Thermochemical Recuperation. This combination enables achieving high thermal efficiency in a wide operating range while mitigating pollutant emissions. This work reports for the first time on results of the RefCCI concept experimental prove and investigation. The experiment findings confirm the results of the previous numerical studies. In addition, new important knowledge was gained on engine performance and emissions dependence on the injection timing of the primary and reformate fuels, as well as on the fuel mixture reactivity. The results show the thermal efficiency improvement by 4–9% (relative) compared to the same engine operation in diesel mode. In the RefCCI mode, the CO emission is lowered with the increase of load, contrary to the trend in the diesel mode. As expected, NOx and total particle number emissions are significantly lower than with the diesel counterpart. The emission of nucleation mode particles is fairly similar to diesel, but the number of accumulation mode particles is reduced by the order of magnitude.

Effects of n-heptane/toluene/ethanol ternary fuel blends on combustion, operating range and emissions in premixed low temperature combustion

Low temperature combustion engines are a new combustion model that the reduction of nitrogen oxide emissions and the increasing of the thermal efficiency can be observed simultaneously. In addition, the problem of misfire at low engine loads and knocking at high engine loads occurs. The fuels have low octane number can be used to eliminate the misfire problem at low engine loads, and the fuels have high octane number can be used to eliminate knocking problem at high engine loads. In this study, the operating ranges of low and high reactivity fuel mixtures with different chemical properties were experimentally investigated in a low temperature combustion engine. While high reactivity n-heptane, T10 and E10 fuels were used, it was seen to be suitable for HCCI strategy in wider and leaner mixing conditions, while low reactivity E20 and E30 showed good performance at high engine loads close to the knocking zone. The highest brake thermal efficiency was obtained as 44.5% with E30 fuel under extremely lean mixture conditions (ʎ = 2.95). While E20 fuel shows a good performance like E30, the fact that most of the combustion takes place before TDC in the use of high reactivity fuel caused low efficiency due to knock and heat losses. It can be stated that ethanol has low reactivity needs high inlet air temperature, high compression ratio or combustion improving additives such as n-heptane and toluene to be used in HCCl applications. The results obtained support the idea of fuel flex vehicles for the current engine.

Effect of piston bowl geometry and compression ratio on in-cylinder combustion and engine performance in a gasoline direct-injection compression ignition engine under different injection conditions

Low temperature combustion (LTC) of high-octane number fuels in compression ignition engines offers an opportunity to simultaneously achieve high engine thermal efficiency and low emissions of NOx and particulate matter without using expensive after-treatment technologies. LTC engines are known to be sensitive to the operation conditions and combustor geometry. It is important to understand the fundamental flow and combustion physics in order to develop the technology further for commercial application. A joint numerical and experimental investigation was conducted in a heavy-duty compression ignition engine using a primary reference fuel with an octane number of 81 to investigate the effects of injection timing, piston geometry, and compression ratio (CR) on the fuel/air mixing and combustion covering different regimes of LTC engines, homogeneous charge compression ignition (HCCI), partially premixed combustion (PPC), and the transition regime from HCCI to PPC. The results show that with the same combustion timing, a higher CR leads to a lower NOx, but a higher emission of UHC and CO. The piston geometry shows a significant impact on the combustion and emission process in the transition regime while it has minor influence in the HCCI and PPC regimes. It is found that high engine efficiency and low emissions of NOx, CO and UHC can be achieved in the earlier PPC regime and later transition regime. The fundamental reason behind this is the stratification of the mixture in composition, temperature and reactivity, which is dictated by the interaction between the spray and the cylinder/piston walls.

Prospective fuels for diesel low temperature combustion engine applications: A critical review

Low Temperature Combustion (LTC) strategies are most promising to simultaneously reduce oxides of nitrogen (NOx) and soot emissions from diesel engines along with offering higher thermal efficiency. Commercial wide spread implementation of diesel LTC strategies requires several challenges to be addressed, including lack of precise ignition timing control, widening the narrow operating load ranges and reducing high unburned fuel emissions. These challenges can be addressed through modifications in the engine or fuel design or both. The timing and rate of combustion in several LTC strategies are controlled primarily by the chemical kinetics of the fuel. Since, diesel fuel reactivity and volatility are tailor-made to perform well under conventional diesel combustion conditions, its application in LTC poses several problems, as highlighted in this paper. Hence, it is important to identify suitable alternative fuels for the different diesel LTC strategies. The published literature on LTC over the past 25 years is critically analyzed to discuss the evolution of the different diesel LTC strategies, their operability limits, the challenges and the controlling parameters for each strategy. This is followed by in-depth analysis of the role of the fuel and the fuel requirements for each strategy. Further, the importance of adopting a hybrid surrogate modeling approach to enable numerical simulation of diesel LTC is highlighted. A novel attempt of relating various diesel low temperature combustion (LTC) strategies based on the approach followed to achieve positive ignition dwell through different injection strategies, utilizing high exhaust gas recirculation (EGR), and dual fuels is presented. The need for replacing diesel with alternative liquid fuels in LTC strategies is presented by highlighting the fundamental problems associated with diesel fuel characteristics. The review concludes by suggesting potential alternative fuels for various diesel LTC strategies and provides directions for future work to address the challenges facing compression ignition LTC operation.

A Computational Investigation of the Impact of Multiple Injection Strategies on Combustion Efficiency in Diesel–Natural Gas Dual-Fuel Low-Temperature Combustion Engines

AbstractDual-fuel diesel–methane low-temperature combustion (LTC) has been investigated by various research groups, showing high potential for emissions reduction (especially oxides of nitrogen oxide (NOx) and particulate matter (PM)) without adversely affecting fuel conversion efficiency in comparison with conventional diesel combustion. However, when operated at low load conditions, dual-fuel LTC typically exhibits poor combustion efficiencies. This behavior is mainly due to low bulk gas temperatures under lean conditions, resulting in unacceptably high carbon monoxide (CO) and unburned hydrocarbon (UHC) emissions. A feasible and rather innovative solution may be to split the pilot injection of liquid fuel into two injection pulses, with the second pilot injection supporting CO and UHC oxidation once combustion is initiated by the first one. In this study, diesel–methane dual-fuel LTC is investigated numerically in a single-cylinder heavy-duty engine operating at 5 bar brake mean effective pressure (BMEP) at 85% and 75% percentage of energy substitution (PES) by methane (taken as a natural gas (NG) surrogate). A multidimensional model is first validated in comparison with the experimental data obtained on the same single-cylinder engine for early single pilot diesel injection at 310 crank angle degrees (CAD) and 500 bar rail pressure. With the single pilot injection case as baseline, the effects of multiple pilot injections and different rail pressures on combustion and emissions are investigated, again showing good agreement with the experimental data. Apparent heat release rate and cylinder pressure histories as well as combustion efficiency trends are correctly captured by the numerical model. Results prove that higher rail pressures yield reductions of HC and CO by 90% and 75%, respectively, at the expense of NOx emissions, which increase by ∼30% from baseline still remaining at very low level (under 1 g/kWh). Furthermore, it is shown that postinjection during the expansion stroke does not support the stable development of the combustion front as the combustion process is confined close to the diesel spray core.

Experimental and kinetic modeling studies on the auto-ignition of methyl crotonate at high pressures and intermediate temperatures

Biofuels, including biodiesel have the potential to partially replace the conventional diesel fuels for low-temperature combustion engine applications to reduce the CO2 emission. Due to the long chain lengths and high molecular weights of the biodiesel components, it is quite challenging to study the biodiesel combustion experimentally and computationally. Methyl crotonate, a short unsaturated fatty acid methyl ester (FAME) is chosen for this chemical kinetic study as it is considered as a model biodiesel fuel. Auto-ignition experiments were performed in a rapid compression machine (RCM) at pressures of 20 and 40 bar under diluted conditions over a temperature range between 900 and 1074 K, and at different equivalence ratios (ϕ = 0.25, 0.5 and 1.0). A chemical kinetic mechanism is chosen from literature (Gaïl et al. 2008) and is modified to incorporate the low-temperature pathways. The mechanism is validated against existing shock tube data (Bennadji et al. 2009) and the present RCM data. The updated mechanism shows satisfactory agreement with the experimental data with significant improvements in low-temperature ignition behavior. The key reactions at various combustion conditions and the improved reactivity of the modified mechanism are analyzed by performing sensitivity and path flux analysis. This study depicts the importance of low-temperature pathways in predicting the ignition behavior of methyl crotonate at intermediate and low temperatures.

An Investigation on the Performance of an Oxidation Catalyst Using Two-dimensional Simulation with Detailed Reaction Mechanism

Abstract The advent of stricter emission standards has increased the importance of aftertreatment devices and the role of numerical simulations in the evolution of better catalytic converters in order to satisfy these emission regulations. In this paper, a 2-D numerical simulation of a single channel of the monolith catalytic converter is presented by using detailed surface reaction kinetics aiming to investigate the chemical behaviour inside the converter. The model has been developed to study the conversion of carbon monoxide (CO) in the presence of propene (C3H6) for low-temperature combustion (LTC) engine application. The inhibition effect of C3H6 over a wide range of CO inlet concentrations is investigated. Considering both low and high levels of CO concentration at the inlet, the 2-D model predicted better results than their corresponding 1-D counterparts when compared with the experimental data from literature. It was also observed that C3H6 inhibition at high temperatures was significant, particularly for high concentrations of CO compared to low concentrations of CO at the inlet.

Experimental Evaluation of a Custom Gasoline-Like Blend Designed to Simultaneously Improve ϕ-Sensitivity, RON and Octane Sensitivity

<div class="section abstract"><div class="htmlview paragraph">ϕ-sensitivity is a fuel characteristic that has important benefits for the operation and control of low-temperature gasoline combustion (LTGC) engines. However, regular gasoline is not very ϕ-sensitive at low-pressure conditions, meaning that intake boosting (typically P<sub>in</sub> ≥ 1.3 bar) is required to take advantage of this property. Thus, there is strong motivation to design a gasoline-like fuel that simultaneously improves ϕ-sensitivity, RON and octane sensitivity, to make an improved fuel suitable for both LTGC and modern SI engines. In a previous study [SAE 2019-01-0961], a 5-component regulation-compliant fuel blend (CB#1) was computationally designed; and simulations showed promising results when it was compared to a regular E10 gasoline (RD5-87). The current study experimentally evaluates CB#1 in the Sandia LTGC engine and compares the results with those of RD5-87. The RON and octane sensitivity were improved 1.3 and 3.6 units by CB#1, respectively. Similar amounts of intake heat are required to achieve autoignition of CB#1 and RD5-87 at premixed, naturally aspirated conditions, ensuring that CB#1 can operate under HCCI mode as easily as regular gasoline. Furthermore, similar maximum engine loads can be reached with both CB#1 and RD5-87 under premixed, high-boost conditions. The ϕ-sensitivity was evaluated using two metrics. First, starting from well-mixed conditions, the change in CA10 with a specific amount of fuel stratification provides a metric of how the ϕ-sensitivity advances the ignition. Second, the amount of CA50 advancement without knock that is achievable with stratification provides a metric of how the ϕ-sensitivity spreads the heat release. Both metrics showed that CB#1 has a greater ϕ-sensitivity than RD5-87. Additionally, CB#1 has a lower peak heat release rate than RD5-87 for stratified operation with the same combustion phasing because of the larger spread of heat release, leading to lower combustion noise and lower knock propensity. Finally, CB#1 was found to be a more suitable fuel to work with ignition enhancers, such as EHN, compared to RD5-87.</div></div>

Computational Modeling of Diesel Spray Combustion with Multiple Injections

<div class="section abstract"><div class="htmlview paragraph">Multiple injection strategies are commonly used in conventional Diesel engines due to the flexibility for optimizing heat-release timing with a consequent improvement in fuel economy and engine-out emissions. This is also desirable in low-temperature combustion (LTC) engines since it offers the potential to reduce unburned hydrocarbon and CO emissions. To better utilize these benefits and find optimal calibrations of split injection strategies, it is imperative that the fundamental processes of multiple injection combustion are understood and computational fluid dynamics models accurately describe the flow dynamics and combustion characteristics between different injection events. To this end, this work is dedicated to the identification of suitable methodologies to predict the multiple injection combustion process. Two different approaches: Representative Interactive Flamelet model (RIF) and Tabulated Flamelet Progress Variable (TFPV) are compared and multiple n-dodecane Spray A injections from the Engine Combustion Network are simulated using the RANS methods with both standard <i>k</i> − <i>ε</i> and <i>k</i> − <i>ω</i> SST models. Evaluations of different turbulence and combustion models are carried out by comparing computed and measured data in terms of the mixing, penetration, first- and second-stage ignition characteristics, flame structures and soot formation.</div></div>

Diesel and diesel-gasoline fuelled premixed low temperature combustion (LTC) engine mode for clean combustion

A premixed Low Temperature Combustion (LTC) engine is demonstrated for clean combustion and improved efficiency. The change in fuel injection timing and pressure along with the addition of charge dilution (by hot EGR) allows obtaining the clean combustion with diesel and diesel-gasoline (D-G with gasoline 25% by volume) blend. The engine operation shows a lower rate of pressure rise, fuel consumption, near-zero NOx-soot emissions, and improved engine thermal efficiency. Compared to diesel, D-G shows improved engine characteristics for broad fuel injection timing. The improved air-fuel mixing by early fuel injection and stratification by hot exhaust gas retards the start of ignition and hence, heat release and pressure rise rates. The engine load-carrying capacity can be extended without decreasing the engine performance by using a combination of low and high reactivity fuel.

An experimental examination of the effects of n-hexane and n-heptane fuel blends on combustion, performance and emissions characteristics in a HCCI engine

Homogenous charge compression ignition (HCCI) engines are low-temperature combustion engines with high thermal efficiency. The operation range of HCCI engines, which are not directly controlled on combustion, is limited by the problems of knocking and misfiring. At this point, it is aimed to eliminate the problem of knocking at the high engine loads by the charge mixture composition and various operating parameters. In this study, the experiments were performed in a single cylinder, four stroke, port injection HCCI gasoline engine to investigate the effects of n-hexane, n-heptane and n-hexane/n-heptane blends. Combustion characteristics, engine performance and exhaust emissions were determined at different engine speeds (800–1800 rpm), lambda (λ = 1.5–3.0) and inlet air temperatures (60 and 80 °C). Operating range of the HCCI engine was determined by using both pure n-hexane and pure n-heptane fuels. The experiments showed that n-hexane, which has higher octane number than that of n-heptane, has more resistance to knocking. In-cylinder pressure decreased with the increase of lambda for all test fuels. Thermal efficiency increased about 28% by using n-hexane compared to n-heptane at constant lambda (λ = 2.35). The results showed that H75N25 provided larger operating range compared with other test fuels.

Experimental Understanding of Ozone Decomposition inside a Low Temperature Combustion Engine

ABSTRACT Low-temperature combustion engines have the potential to meet pollutant requirements and reduce fuel consumption. The present study, based on an ultraviolet light absorption diagnostic, investigates ozone decomposition inside a single-cylinder compression ignition engine. Experiments were performed under HCCI conditions for non-reactive and reactive cases. Experimental results showed that intake parameters, pressure and temperature, and intake flow composition have a significant impact on ozone decomposition timing. In this study H2O vapor and Isooctane seem to have the most significant impact on ozone decomposition.

An experimental investigation of the injection timing effect on the combustion phasing and emissions in reactivity-controlled compression ignition (RCCI) engine

Nowadays, due to the environmental problems caused by pollution and high fossil fuels prices, the study on the internal combustion engines have attracted many researchers. Investigations show that low-temperature combustion engines play a very effective role in increasing efficiency and reducing emissions. In this research, the effects of diesel fuel injection timing on the performance characteristics of the engine and reducing its emissions were experimentally studied. To do so, a single-cylinder engine equipped with a common rail injection system for controlling the pressure was used. Gasoline fuel was injected through the injector installed in the inlet manifold. The gasoline entered the cylinder as a low-reactivity fuel with inlet air, while the diesel fuel was injected into the cylinder as a high-reactivity fuel by a common rail system and high-pressure injector. Diesel fuel was injected into the cylinder at − 50°, − 40°, − 20°, and − 10° before top dead center (bTDC). The results show that the engine minimum and maximum brake power and efficiency output were observed in the fuel injection timings of − 10 and − 40 bTDC, respectively. Also, it was found that advancing the injection timing increases the ignition delay and plays a very important role in the combustion phasing quality. Besides, findings show that advancing fuel injection timing has a significant effect on NOx and particulate matter (PM) emissions. The lowest and maximum amount NOx emissions occur at the injection timings of − 50° and − 10°, respectively, while for PM emission these values are − 40 and − 50, respectively. According to the results, the injection timing could be one of the most important parameters for controlling the engine that will increase efficiency and reduce emissions.

Autoignition behavior of a full boiling-range gasoline: Observations in RCM and GCI engine environments

The understanding of, and capability to modulate fuel autoignition behavior are important aspects towards the development of advanced, low temperature combustion (LTC) engine concepts, which have potential to significantly increase engine efficiency while at the same time addressing emissions concerns. Proper combustion phasing and control of heat release rates via, for instance, multiple injections and exhaust gas recirculation, are significant challenges that can vary with fuel composition. Overall reactivity, which is a strong function of the in-cylinder temperature and pressure, is a prime driver for regulating combustion timing, while preliminary exothermicity, in the form of low- and intermediate-temperature heat release (LTHR, ITHR) can inhibit, or facilitate operational success, e.g., control combustion phasing. There are still gaps in understanding these features and how they interact with needs of advanced combustion engines, and how practical fuels can be rated for the new challenges of LTC engines.This work utilizes a rapid compression machine (RCM) and gasoline compression ignition (GCI) engine to probe the autoignition behavior of a California Reformulated Gasoline Blendstock for Oxygenate Blending (CARBOB) (RON = 86, MON = 81.4) under quasi- homogeneous charge compression ignition (qHCCI) operation. A wide range of thermodynamic conditions is explored (Tc = 700–1000 K, Pc = 15–90 bar) where ignition delay times and LTHR/ITHR are quantified. Both stoichiometric, dilute (11% O2) and lean (equivalence ratio (ϕ) = 0.23) fuel loading conditions are considered. The GCI engine is operated under fuel-lean conditions (ϕ = 0.23) using no external exhaust gas recirculation over a range of intake temperature (Tin = 30–70 °C), with the intake pressure adjusted (Pin = 1.2–1.3 bar) to achieve constant combustion phasing (CA50 = −4 °aTDC). Preliminary exothermicity is also quantified under these conditions.The stoichiometric, dilute RCM measurements reveal negative temperature coefficient (NTC) behavior for this fuel and indicate that rates and extents of LTHR and ITHR are both affected by the compressed conditions, with temperature imposing an inverse dependence, while increased pressure causes LTHR to increases, but ITHR to decrease. These are the first experimental quantifications of ITHR trends for a practical fuel under well-controlled, static conditions. When the lean RCM measurements are mapped to the in-cylinder conditions of the engine, it is found that under a constant combustion phasing scenario (as used in the engine), the fuel has little overall temperature sensitivity, while the starts of high temperature heat release (soHTHR) and top dead center (TDC) points seen along the engine compression trajectories correspond to isopleths of ignition delay times τRCM = 6 and 3 ms, respectively. In addition, the points of peak LTHR rate in the engine correspond to an isopleth of first-stage ignition τ1,RCM = 0.50–0.75 ms. Correlating the magnitudes of LTHR and ITHR measured in the RCM to the engine requires quantification of the preliminary exothermicity at the thermodynamic conditions of peat LTHR rate and soHTHR, respectively. The current measurements demonstrate how fundamental data from an RCM can be used to project expected trends in overall fuel reactivity to a qHCCI engine environment, and thus provide a possible avenue for characterizing fuels for LTC engines.

Kinetic effects of n-propylbenzene on n-dodecane counterflow nonpremixed cool flames

The development of alternative drop-in fuels and fuel blends with petroleum-derived fuels necessitate an understanding of the kinetic interactions between aromatics and alkanes for the development of advanced low-temperature combustion engines. In the present study, the role of aromatic chemistry on n-alkane low-temperature chemistry is investigated by using nitrogen-diluted nonpremixed cool flames of n-dodecane/n-propylbenzene blends in an atmospheric counterflow burner. Effects of aromatic addition on n-alkane reactivity are examined by fixing the concentration of n-dodecane while varying the ratio of nitrogen/n-propylbenzene. The cool flame structure is probed using formaldehyde laser-induced fluorescence and thermocouple thermometry, and measurements of the cool flame and hot flame extinction limits are obtained. Fundamental differences between the response of cool flame and hot flame heat release and radical production to stretch are also discussed. The results show that, while the specific heat release rate characterizes the burning intensity of a hot flame, the same is not true for a cool flame due to the competition between reactant leakage and negative temperature coefficient reactivity. It is also found that, contrary to hot flames, in cool flames the addition of n-propylbenzene promotes n-dodecane cool flame extinction. Kinetic analysis reveals that aromatics act as a sink of hydroxyl and hydroperoxyl radicals in cool flames by forming stable oxygenated aromatics due to the low flame temperatures. As a result, the low-temperature reactivity of n-dodecane is significantly inhibited by the addition of aromatics, even relative to inert substitution. The present experimental results are valuable for comprehensive chemical kinetic model development and validation.

Intake charge temperature effect on performance characteristics of direct injection low-temperature combustion engines

The low-temperature combustion (LTC) concept presents solutions for simultaneous reduction in pollution and fuel consumption of internal combustion engines. However, the most important challenges of this concept are the lack of any direct combustion phasing control method and the limited operating range. Two LTC concepts, namely direct injection (DI) homogeneous charge compression ignition (HCCI) and partially premixed combustion, together with DI diesel can be combined to provide the desired performance for the whole load range. Although this combination provides the solution for the limited operating range, there still remains the problem with the method for combustion phasing control. Inlet temperature modulation may be used to regulate the combustion phasing. Therefore, this study investigates the effect of the intake charge temperature on the DI-HCCI combustion. The investigations are based on a novel two-stage combustion model. The combustion is predicted with the single-zone approach from the intake valve closing to the end of injection. Thereupon, it is predicted by the multi-zone approach. The results indicate that intake charge temperature has profound effects on in-cylinder charge pressure and temperature. It alters heat release rate magnitude and phasing, thus changing combustion timing. Moreover, this parameter affects indicated delivered power of the DI-HCCI combustion engine.

Effect of Ambient Pressure on Macroscopic Spray Characteristic of Various Biodiesel Fuels

This study deals with the experimental and the theoretical spray tip penetration characteristics of diesel and various biodiesel fuels for charge formation in low temperature combustion engines. A theoretical modified Roisman correlation is validated for far-field spray tip penetration of biodiesel spray based on fuel properties. The biodiesel viscosity is a dominant property affecting the spray characteristics in the model. The modified Roisman correlation is validated with experimental spray tip penetration characteristics for low to high ambient gas densities. The use of unsaturated biodiesel shows a high spray tip penetration even at high ambient gas density. The use of multiple fuel injection technique in low temperature combustion engines with unsaturated biodiesel can be helpful in achieving the optimum charge formation.

Study on the effects of intake conditions on the exergy destruction of low temperature combustion engine for a toluene reference fuel

Low temperature combustion (LTC) is a new mode for efficient and clean combustion in engines, and the process is mainly controlled by chemical reaction kinetics of fuel. In this paper, the numerical model of exergy analysis for LTC engine was established. The temperature, pressure and species concentration were obtained by using the homogeneous charge compression ignition (HCCI) engine model of Chemkin-Pro software with the simplified mechanism of toluene reference fuel (TRF). The exergy items were further calculated to explore the effect of different intake conditions on exergy destruction in LTC process. It was found that the irreversibility related to the combustion proceeding mainly happened in low temperature and high temperature reaction zones. With the increase of exhaust gas recirculation (EGR) rate, the proportion of working exergy increases but the irreversibility destruction of combustion decreases. Besides, N2 component concentration in EGR gas has the greatest influence on the distribution of exergy.