Low Temperature Combustion Concepts Research Articles

The Experimental Investigation of the Effects on the Combustion, Performance, and Emission Characteristics of an RCCI Engine Using Methanol/Diesel Fuel

Reactivity-controlled compression ignition (RCCI) combustion is considered one of the most promising low-temperature combustion (LTC) concepts aimed at reducing greenhouse gases for the transportation and power generation sectors. RCCI combustion mode is achieved by combining different fuel types with low and high temperatures. The aim of this study is to investigate combustion characteristics and reduce nitrogen oxide (NOx) and carbon dioxide (CO2) emissions. In this experimental study, the effects of the RCCI strategy using methanol/diesel fuel on combustion characteristics (ignition delay, combustion duration), engine performance (brake-specific fuel consumption and brake-specific energy consumption), and emissions were examined in a four-cylinder, turbocharged, dual-fuel engine. The experiments were conducted at a constant speed of 1750 rpm at partial loads (40 Nm, 60 Nm, 80 Nm, and 100 Nm). The test results obtained with diesel fuel were compared with the test results obtained with methanol at different mass flow rates. When the results were examined, the minimum ignition delay (ID) occurred at 40 Nm torque, 5.63 crank angle (CA) with M12 fuel, while the maximum ID occurred with M26 fuel at 80 Nm torque, showing an increasing trend as engine load (EL) increased. The highest combustion time (CD) was achieved with M26 fuel at 100 Nm torque, whereas the lowest was achieved with the same fuel (M26) at 40 Nm. While the minimum brake-specific fuel consumption (bsfc) was 45.9 g/kWh for conventional diesel fuel at 40 Nm, the highest bsfc was 104.88 g/kWh for 100 Nm with M26 fuel. Generally, bsfc tends to increase with increasing load. Brake-specific energy consumption (bsec) had the lowest value of 1950.58 kJ/kWh with conventional diesel fuel at 40 Nm and the highest value of 4034.69 kJ/kWh with M26 fuel at 100 Nm. As the methanol content increased, significant improvements were observed in (NOx) and (CO2) emissions, while hydrocarbon (HC) and oxygen (O2) emissions increased as well. Smoke emissions decreased at low loads but tended to increase at high loads.

Effect of split injection strategy of diesel fuel on multi-stage heat release and performance of a RCCI engine fueled with diesel and natural gas

Reactivity controlled compression ignition (RCCI) combustion is a advanced low temperature combustion concept to reduce CO2 and brake the trade-off between NOx and PM emissions for next generation compression ignition (CI) engines. However, it leads to the more complex multi-stage heat release in diesel/natural gas (NG) dual fuel engines and is criticized for extra-high methane and carbon monoxide emissions. Using the existing methods, it is difficult to effectively quantify the contribution of the accumulated heat release (AHR) at each stage to the whole combustion process and to create their relevance to the performance and emissions in the RCCI engines.In this paper, experiments were conducted on a ship diesel/NG dual-fuel engine at a load of 25 %. A new identification and quantitative analysis method of multi-stage heat release is proposed, and the coupling effects of the diesel split injection parameters on the multi-stage heat release and performance in the RCCI engine were revealed. The results show that the new method is not only available for analyzing the combustion of traditional CI engines but also is more effective for identifying the multi-stage combustion in RCCI engines. For the increased pre-injection ratio (PR), as the start of first injection (SOI-I) and the start of second injection (SOI-II) advance, the AHR in Stage-I (Q-Stage-I) decreases, and the increased Q-Stage-III lead to the improved indicated thermal efficiency (ITE > 49 %). Meanwhile, methane (CH4), non-methane hydrocarbon (NMHC) and carbon monoxide (CO) emissions can be reduced by more than 50 %, while nitrogen oxides (NOx) emissions increase. The impact significance of SOI-II on Q-Stage-I and Q-Stage-III is higher, their values are + 65.88 % and −51.04 %, respectively, and the Q-Stage-II is mainly controlled by SOI-I. The impact significance of Q-Stage-III on ITE is the highest about + 69.43 %. Q-Stage-I shows a higher positive correlation with CH4, NMHC and CO emissions although the proportion of Q-Stage-I is far smaller than that of Q-Stage-II and Q-Stage-III. Therefore, the simultaneous reduction of incomplete combustion products and NOx emission can be achieved by reasonably adjusting split injection parameters.

Ultra-low emission power generation utilizing chemically stabilized waste plastics pyrolysis oil in RCCI combustion concept

Emission standards in European Union, designed to reduce the environmental impact of power generation, present a significant challenge for fast-response distributed power generation systems based on internal combustion engines. Regulated emissions, such as NOx and particulate matter present a major concern due to their adverse number of environmental and health effects. Simultaneously, European Union strives towards sustainable management of plastic waste and seeks the ways for its upcycling and production of new fuels and chemicals. As an answer to the presented challenges, the present experimental study addresses the potential for use of chemically stabilized Waste Plastics Oil (WPO), a product of pyrolysis process of waste plastics in a Reactivity Controlled Compression Ignition (RCCI) combustion concept. To establish a reactivity-controlled combustion, the study uses a combination of methane (a model fuel for biomethane) and WPO to a) simultaneously reduce NOx and particulate matter emissions due to low local combustion temperatures and a high degree of charge homogenization and b) address waste and carbon footprint reduction challenges. Through experiments, influence of direct injection timing and energy shares of utilized fuels to in-cylinder thermodynamic parameters and engine emission response were evaluated in engine operating points at constant indicated mean effective pressure. Acquired results were deeply investigated and benchmarked against compression ignition (CI) and RCCI operation with conventional diesel fuel to determine potential for WPO utilization in an advanced low-temperature combustion concept. Results show that chemically stabilized WPO can be efficiently utilized in RCCI combustion concept without adaptation of injection parameters and that with suitable control parameters, ultra-low emissions of NOx and PM can be achieved with utilized fuels. For diesel/methane mix, NOx and PM emissions were reduced compared to conventional CI operation for 82.0% and 93.2%, respectively, whereas for WPO/methane mix, NOx and PM emissions were reduced for 88.7% and 97.6%, respectively, which can be ascribed to favourable chemical characteristics of WPO for the utilized combustion concept. In the least favourable operating point among those studied, indicated mean effective pressure covariance was kept below 2.5%, which is well below 5% being considered the limit for stable engine operation.

Experimental Characterization of Hydrocarbons and Nitrogen Oxides Production in a Heavy-Duty Diesel–Natural Gas Reactivity-Controlled Compression Ignition Engine

Reactivity-Controlled Compression Ignition (RCCI) combustion is considered one of the most promising Low-Temperature Combustion (LTC) concepts aimed at reducing greenhouse gases for the transportation and power generation sectors. Due to the spontaneous combustion of a lean, nearly homogeneous mixture of air and low-reactivity fuel (LRF), ignited through the direct injection of a small quantity of high-reactivity fuel (HRF), RCCI (dual-fuel) shows higher efficiency and lower pollutants compared to conventional diesel combustion (CDC) if run at very advanced injection timing. Even though a HRF is used, the use of advanced injection timing leads to high ignition delays, compared to CDC, and generates high cycle-to-cycle variability, limited operating range, and high pressure rise rates at high loads. This work presents an experimental analysis performed on a heavy-duty single-cylinder compression ignited engine in dual-fuel diesel–natural gas mode. The objective of the present work is to investigate and highlight the correlations between combustion behavior and pollutant emissions, especially unburned hydrocarbons (HC) and oxides of nitrogen (NOx). Based on the analysis of crank-resolved pollutants measurements performed through fast FID and fast NOx systems under different engine operating conditions, two correlations were found demonstrating a good accordance between pollutant production and combustion behavior: Net Cyclic Hydrocarbon emission—cyclic IMEP variations (R2 = 0.86), and Cyclic NOx—maximum value of the Rate of Heat Released (R2 = 0.82).

A Review on Recent Developments of RCCI Engines Operated with Alternative Fuels

Environmental concerns over automotive exhaust emissions and consumer demand for higher fuel efficiency have led to the development of low-temperature combustion concepts. The reactivity-controlled compression ignition (RCCI) engine is one among them and has the potential to reduce NOx and smoke emissions simultaneously. In this concept, a low-reactivity fuel is injected into the intake port and another high-reactivity fuel is injected into the cylinder directly. This results in reactivity stratification and provides more control over the rate of heat release. However, operating parameters such as reactivity of fuels, premixing ratio, injection strategies, exhaust gas recirculation ratio, piston bowl geometry, and compression ratio influence emissions formation. The article reviews recent developments on the effect of the above operating parameters on the performance and emission characteristics of RCCI engines operated with alternative fuels. The combustion strategies used to extend the RCCI mode to higher loads are also reviewed. Applications of computational fluid dynamics (CFDs) to design the combustion chamber for RCCI engines are discussed. The need for further improvements in the CFD models for RCCI engines is explained. After presenting a thorough review of recent literature, directions for future research on RCCI engines are proposed.

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.

Understanding the effect of Intake temperature on the ϕ-sensitivity of toluene-ethanol reference fuels and neat ethanol

The low-temperature combustion (LTC) is an attractive concept that enables the modem combustion engines to move toward sustainability mainly by increasing the efficiency and decreasing the emissions. The modern combustion engines which are working based on the LTC concept have specific fuel requirements. Fuel ϕ-sensitivity is a key factor to be considered for tailoring fuels for these engines. Fuel with a high ϕ-sensitivity are more responsive to thermal or fuel stratifications; the auto-ignition properties of different air-fuel mixtures of these fuels, with different equivalence ratio (ϕ), are more diverse. This diversity provide a smoother heat release rate in stratified condition. In this study 11 different toluene–ethanol reference fuels (TERFs) in three research octane number (RON) groups of 63, 84, and 105 together with neat ethanol are evaluated. The Lund ϕ-sensitivity method is used to evaluate these fuels in a cooperative fuel research (CFR) engine. The effect of variation of intake temperature on pressure sensitivity of fuel at a constant combustion phasing is evaluated. This evaluation is performed at two intake temperature of 373 and 423 K, and the results are compared with the outcome of the Lund ϕ-sensitivity number with the intake temperature of 323 K. This study shows that the CR sensitivity response of different blends to the intake charge temperature variation depends on the fuel composition. Accumulated low temperature heat release and latent heat of vaporization. It proves that the fuel ϕ-sensitivity will vary under different thermodynamic conditions. There was a clear link between the accumulated heat released during the early reaction and CR sensitivity of the blends at different intake temperature of 373 and 423 K but the link with the latent heat of vaporization (HoV) found to be inexplicit.

Development of a phenomenological model for the description of RCCI combustion in a dual-fuel marine internal combustion engine

Increasingly stringent pollutant and CO2 emission standards require engine manufacturers to investigate innovative solutions. Among these techniques, low-temperature combustion (LTC) concepts have a large potential to simultaneously reduce NOx emissions and fuel consumption. A promising manner to realize LTC consists of adopting ultra-lean mixtures, where the combustion evolution is controlled by a proper spatial distribution of fuels with different chemical reactivities. In this context, depending on the proportion and stratification of the fuels, the heat release can primarily depend on chemistry progression, leading to a Reactivity Controlled Compression Ignition (RCCI) mode, or on flame propagation, locally initiated by a high reactivity fuel.In this work, the combustion characteristics of a large-bore research engine are experimentally investigated. Natural gas is supplied into the intake port, while light fuel oil (LFO) is directly injected in the cylinder. An experimental campaign is carried out including sweeps of engine load, air/fuel proportion, LFO amount, valve timing, and intake air temperature. Global engine operating parameters as well as cylinder pressure traces are recorded and analyzed.Based on the available experimental data, a phenomenological model handling both chemistries of fuels with different reactivities and flame propagation is developed and validated. The model is based on a multi-zone approach, where auto-ignition chemistry is solved by a tabulated method to preserve the computational effort. The proposed numerical approach shows the ability to simulate the experimental data with good accuracy, using a fixed tuning constant set. A dedicated correlation is built to reproduce the expected in-cylinder distribution of the directly injected liquid fuel. Global performance and combustion parameters are predicted with an average error below 5%. The model demonstrates to correctly describe the behavior of the tested engine under different operating conditions and to capture the physics behind such advanced combustion concepts.

A comparative study on gasoline/diesel-fueled RCCI combustion at different premixed ratios and high-EGR diesel CI combustion in an IC engine under low load conditions

Low temperature combustion concepts in internal combustion engines have arisen as one of the solutions that reduce NOx and particulate emissions without a fuel consumption penalty. Among the combustion concepts, reactivity controlled compression ignition (RCCI) has the potential of being able to be achieved in a wider operating range than other low temperature concepts. On the other hand, exhaust gas recirculation (EGR) use in diesel-compression ignition (CI) engines is an effective way to reduce NOx emission. This study experimentally investigated the high-EGR CI fueled with diesel and gasoline/diesel fueled RCCI combustion modes in terms of combustion, performance, and emission at fixed energy inputs corresponding to low load conditions for different engine speeds. In RCCI combustion mode, different premixed ratios were also tested to determine their effects. The results show that CA50 locations in all high-EGR CI combustion occurred later than those of RCCI modes, which led to late peak pressure occurrence. By considering heat release rate curve characteristics, the controlled combustion phase emerged at the highest premixed ratio in RCCI as in the high-EGR CI combustion. RCCI combustion showed an improvement in smoke emissions, and the maximum improvement was attained by about 86%. In RCCI combustion, nitrogen oxide (NO) emissions at 2000 rpm engine speeds are significantly lower than that in high-EGR CI whereas the increasing premixed ratio at 1500 and 1750 rpm led NO emission to increase. Besides, RCCI combustion with the highest premixed ratios resulted in slightly higher brake thermal efficiencies (BTE). The maximum difference in BTE values was obtained by about 3.0% in favor of RCCI combustion.

2-Stroke RCCI Engines for Passenger Cars

Reactivity Controlled Compression Ignition (RCCI) is one of the most promising solutions among the low temperature combustion concepts, in terms of thermal efficiency and pollutant emissions. However, for values of brake mean effective pressure higher than 10 bar, in-cylinder peak pressure rise rates tend to be too high, limiting the specific power of any 4-Stroke (4S) engine. Such a limitation can be canceled by moving to the 2-Stroke (2S) cycle. Among many alternatives, the “Uniflow” scavenging system with exhaust poppet valves on the cylinder head allows the designer to reproduce the same identical combustion patterns of a 4-stroke RCCI engine, while increasing the indicated power output. The goal of the paper is to explore the potential of a 2-stroke RCCI engine, on the basis of a comprehensive experimental campaign carried out on a modified automotive 2.0 L, 4-stroke, four-cylinder, four-valve diesel engine. The developed prototype can run with one cylinder operating in 4-stroke RCCI mode (gasoline–diesel), while the others work in the standard diesel mode. A One Dimensional-Computational Fluid Dynamics (1D-CFD) model has been built to predict the performance of the same prototype, when operating all four cylinders in RCCI mode. In parallel, an equivalent 2-stroke RCCI virtual engine has been developed, by means of 1D-CFD simulations and empirical assumptions. A numerical comparison between the 4S and the 2S engines is finally presented, in terms of performance and emissions at full load. The study demonstrates that a 2S RCCI engine can maintain all of the advantages of the RCCI combustion, strongly reducing the penalization in terms of performance, in comparison to a standard 4S diesel engine.

Development of an empirical test method to quantify the ɸ-sensitivity of liquid fuels

Several researchers are investigating strategies to lower the emissions and increase the efficiency of combustion engines to reduce the negative impact on the environment and the climate from transportation. The low-temperature combustion (LTC) concept is the basis for some of these high-efficiency, low-emission combustion technologies. To maximize the combustion controllability of engines based on the LTC concept, the combustion behavior of fuel both at different equivalence ratios (ɸ) and under ɸ sweeps must be understood and planned precisely. The ɸ-sensitivity of a fuel explains its behavior at different engine loads or stratification levels. In this study, a new test method for empirically evaluating ɸ-sensitivity using a Cooperative Fuel Research (CFR) engine is proposed and the validity of the method is investigated. A modified CFR engine for homogeneous-charge compression ignition (HCCI) combustion is used to investigate the compression ratio (CR) sensitivity of different toluene–ethanol reference fuels (TERFs) in a research octane number (RON) range of 63–105. This study suggests a method to quantify the ɸ-sensitivity of different fuels and blends by measuring the compression ratio required to keep the CA50 constant while varying ɸ. It shows that the fuel composition greatly affects the fuel ɸ-sensitivity even for different blends with the same RON. The results also indicate that the coexistence of ethanol and toluene in a blend can generate the highest ɸ-sensitivity of the blend compared to other blends with the same RON. Fuel composition has a strong effect on emissions. The simultaneous effect of fuel composition and ɸ variation on the emission and stability parameters is nonlinear.

Leveraging hydrogen as the low reactive component in the optimization of the PPCI-RCCI transition regimes in an existing diesel engine under varying injection phasing and reactivity stratification strategies

This research illustrates the novel interposed zone of partially premixed and reactivity-controlled combustion in conjunction with injection phasing and reactivity phasing strategies to understand the performance emission and stability characteristics of a single-cylinder common rail direct injection diesel engine. However, this study determined the optimum interposed zone of operation using Response Surface Methodology (RSM). The findings indicate that raising the rate of hydrogen induction enhances the stability of interposed zone of combustion. The interposed optimum regime has a 31.58% exergy efficiency and 99.1% desirability. Compared to the similar trial run, the optimization study revealed a 45.09% reduction in Soot, a 14.29% reduction in total unburnt hydrocarbon (TUHC), and a 39.83% reduction in NOx emission levels. Thus, experimental and predicted values have been compared. Hence, this variable injection and reactivity phasing under hydrogen enrichment strategies are feasible enough to achieve the goals of advanced low-temperature combustion (LTC) concepts in an existing diesel engine without making significant design modifications.

Combustion stability control of gasoline compression ignition (GCI) under low-load conditions: A review

Abstract With greater energy pressure and stricter emission standards, increasing power output and reducing emissions of engines are simultaneously required. To achieve this, considerable researches are motivated. In recent years, key and representative developments in the field of high-efficiency and clean engines have been carried out. Among them, a low temperature combustion concept called gasoline compression ignition (GCI) is widely considered by universities and research institutions around the world, since it has the potential to achieve ultra-low NO X and soot emissions while maintaining high thermal efficiency. However, GCI combustion mode has certain issues to be solved, such as combustion instability under low-load conditions. Therefore, this paper reviews the experimental, computational and optical studies on the combustion stability control of GCI combustion mode during low loads and describes the recent progress to improve combustion stability as well as points out the future work finally.

LTC performance of C1–C4 water-alcohol blends with the same cooling potential

Alcohols are renewable fuels with high cooling potentials and low φ-sensitivity, ideal properties for highly controllable low temperature combustion (LTC) concepts that enable high-efficiency, low-emissions operation. Recent work showed that the C1–C4 alcohols behave similarly in LTC. The primary difference between these fuels is their cooling potential, which impacts their stratified LTC behavior. To homogenize the stratified LTC performance of these fuels and create an equivalence class of fuels, water can be blended with these fuels to increase their cooling potential to some benchmark value. When ethanol or propanol is blended with water to WE80 (80% ethanol, 20% water) or WP70, no significant change in the sensitivity of the fuel to operating conditions occurs, with a 1–2 percentage point decrease in combustion efficiency and a slight decrease in NOx occurring with WP70. The isomers of butanol are not fully miscible with water and require a C1–C3 alcohol as a co-solvent. W25E50B25 (25% water, 50% ethanol, and 25% of one of the three butanol isomers (n-, iso, or sec-)) behaved similarly to WE80. The ethanol in the blend was able to mute the cool flame reactivity of n-butanol and sec-butanol, further homogenizing the LTC performance of these fuels. Overall, when ethanol, propanol, or butanol are blended with water to have the same cooling potential as methanol, there is no appreciable difference in their LTC performance (demonstrating interchangeability) other than a small combustion efficiency penalty, particularly at low loads. When load increases or when combustion is advanced, this penalty decreases.

Individual cylinder fuel blend estimation in a dual-fuel engine using an in-cylinder pressure based observer

Cylinder-to-cylinder combustion dispersion in internal combustion engines might be caused by various factors (e.g. manufacturing variations of the injectors or nozzle coking) which can result in an increase in pollutant emissions. When dealing with low temperature combustion concepts such as premixed dual-fuel, the system might suffer from an additional source of dispersion due to port fuel injection distribution. Conventional cylinder fuel concentration estimation is based on look-up tables previously calibrated and saved in the ECU. The aging and the fuel distribution characterization of the injectors are a challenging task when relying only on a single UEGO sensor placed at the exhaust. In-cylinder pressure sensors offer a powerful solution to evaluate the energy released by the fuel with one cycle resolution. The present work proposes to combine the information provided by such sensor together with conventional sensors, in this case air mass flow and lambda sensor, for estimating the fuel concentration and blending ratio entering each cylinder in a heavy-duty dual-fuel engine. A Kalman filter was designed to tackle the dynamics of the system, e.g. lambda sensor delay and port fuel distribution, and validated in both conventional diesel and dual-fuel combustion. The output of the filter was then used to update the injectors look-up table in order to cope with aging and possible bias over time.

A comprehensive experimental investigation of low-temperature combustion with thick thermal barrier coatings

Thick thermal barrier coatings (TBCs) have a significant potential to increase thermal efficiency by reducing heat transfer losses. However, in conventional combustion modes, the drawbacks associated with charge heating and higher propensity to knock have outweighed the efficiency benefits. Since the advanced low-temperature combustion (LTC) concepts are fundamentally different from the conventional combustion modes, these penalties do not exist in most of LTCs.The current experimental study shows the feasibility and benefits of thick TBCs with advanced LTC enabled by two different fuels: conventional gasoline and wet ethanol 80 (WE80, i.e., 80% ethanol and 20% water by mass). A total of five pistons were tested, including two metal baselines and three TBC-coated pistons with different thicknesses or surface finishes. A load sweep was conducted with each fuel on each piston within the same constraints. The thick TBCs extends the low load limit by about 15% for both gasoline and WE80 cases. A deterioration of the high load limit was not observed, which implies that the charge heating penalty does not occur in LTCs. The combustion efficiency increased for the thicker TBC by up to 2% points, and the fuel conversion efficiency was increased by up to 4.3%. The gasoline cases experience the largest benefits at low load, while the wet ethanol experiences the largest benefits at mid-to-high load. The intake temperature requirement is successfully reduced by 10–15 K. It is also observed that the dense sealing layer results in a significant improvement to UHC emissions. All of the coated pistons survived the 10–20 h of engine operation with no visual failure.

Hydrogen energy share enhancement in a heavy duty diesel engine under RCCI combustion fueled with natural gas and diesel oil

The aim of this study is to enhance hydrogen energy share in a RCCI engine. The engine under consideration is fueled with diesel oil and natural gas enriched with hydrogen or syngas and is set to operate at 9.4 bar gross indicated mean effective pressure (Mid- Load). The syngas used in this study consists of hydrogen and carbon monoxide which are mixed together on a volumetric ratio of 80:20. A fixed amount of diesel oil is injected per cycle into the combustion chamber of the RCCI engine. Based on two different strategies, hydrogen or syngas mixed with exhaust gas recirculation are admitted gradually along with natural gas while ensuring that always the low temperature combustion concept is fulfilled. The RCCI engine operation is simulated through commercial software coupled with chemical kinetics solver. The simulation results show that without any engine diesel knock occurrence, by adding hydrogen to natural gas, the share of hydrogen energy could be increased up to 40.43% while the engine power output is reduced only by about 1%. Also, syngas addition to natural gas causes that the share of hydrogen energy could be increased up to 27.05% while improves the engine power more than 4%. At the same time, by considering two mentioned strategies, the overall hydrocarbon fuel consumption per cycle can be reduced by up to 46.60% and 33.86%, respectively. Moreover, having the gross indicated efficiency of well over 50% and significant reduction in the engine emissions compared to RCCI combustion fueled solely with natural gas and diesel oil are achievable.

Experimental Investigation of Performance and Emissions of Ethanol and n-Butanol Fuel Blends in a Heavy-Duty Diesel Engine

Alcohol fuels are potential alternative fuels for low-temperature combustion concepts in internal combustion engine applications. In this work, 80 vol% of ethanol and 80 vol% of n-butanol are blended with 20 vol% of n-heptane, respectively. These two alcohol fuel blends are investigated in a combustion research unit and a single-cylinder heavy-duty engine to compare the combustion and emission characteristics. The effects of EGR rate and achievable operating load range when using ethanol and n-butanol are the major goals of this investigation. The results show that the ethanol fuel blend requires much higher temperatures to auto-ignite than do the n-butanol blend and diesel. Both alcohol fuel blends show negligible soot emissions in the medium load range when operated with a 40% EGR rate. However, the ethanol fuel blend produces more nucleation mode particles and fewer accumulation mode particles compared to the n-butanol fuel blend under the same operating condition. Furthermore, the particulate size distribution shows that diesel generates more particles with larger particle diameters and thus more soot mass compared to alcohol fuel blends. Still, both alcohol fuel blends can be operated from low to high load with simultaneous reduction of NOx and soot emissions but at the cost of increased HC and CO emissions. The Euro VI-regulated soot mass and particle number are achieved from low to medium-high load for alcohol fuels. Diesel has the great advantage of achieving high combustion efficiency but shows a NOx/soot tradeoff at a high EGR rate. Generally, the ethanol fuel blend yields the lowest gross indicated efficiency in the whole test range compared to diesel and the n-butanol fuel blend due to the necessity of inlet heating, which decreases the thermal efficiency. The n-butanol fuel blend achieves the highest gross indicated efficiency (above 50%) in the medium-high load range.

Infrared/Visible Optical Diagnostics of RCCI Combustion with Dieseline in a Compression Ignition Engine

<div class="section abstract"><div class="htmlview paragraph">Compression ignition engines are widely used for transport and energy generation due to their high efficiency and low fuel consumption. To minimize the environmental impact of this technology, the pollutant emissions levels at the exhaust are strictly regulated. To reduce the after-treatment needs, alternative strategies as the low temperature combustion (LTC) concepts are being investigated recently. The reactivity controlled compression ignition (RCCI) uses two fuels (direct- and port- injected) with different reactivity to control the in-cylinder mixture reactivity by adjusting the proportion of both fuels. In spite of the proportion of the port-injected fuel is typically higher than the direct-injected one, the characteristics of the latter play a main role on the combustion process. Use of gasoline for direct injection is attractive to retard the start of combustion and to improve the air-fuel mixing process. In this work, the influence of the direct-injected fuel properties on RCCI combustion mode is studied in an optical compression ignition engine. Gasoline fuel is injected in the intake manifold while a blend of gasoline and diesel (a.k.a. dieseline) is directly injected into the cylinder. Non-conventional optical diagnostics in the visible and infrared spectra are applied for the direct investigation of the in-cylinder phenomena during the injection and the combustion processes. A low-luminosity, mainly kinetically controlled combustion mode has been observed.</div></div>

Study of spray/wall interaction in transition zones from HCCI via PPC to CI combustion modes

Low-temperature combustion concepts like homogeneous charge compression ignition (HCCI) and partially premixed combustion (PPC) offer the benefit of higher engine efficiency while keeping lower exhaust emissions. In this study, a full-transparent optical engine is employed to investigate the effect of fuel spray/wall interactions on combustion characteristics for transition in combustion mode from HCCI, via PPC to CI. Planar laser-induced fluorescence (PLIF) imaging of acetone and high-speed natural flame luminosity imaging techniques are applied to visualize fuel spray/wall interactions, fuel distribution, and combustion development processes. The combustion phasing, IMEP as well as engine-out emissions are analyzed to study the relationships between fuel spray, combustion, and emissions. The experimental results show three distinct zones with different fuel injection timings: the transitional zone between HCCI and PPC, the PPC zone, and the transitional zone between PPC and CI. The fuel/wall impingement position, fuel penetration and distribution, as well as combustion stratification, are investigated in these three zones. Both CA10 (the crank angle when 10% of the overall heat is released) and CA50 followed similar trends at different injection timings and present obvious “bowl” shapes in the PPC zone. Moreover, more fuel distribution near the cylinder wall and crevice is related to the increased UHC emission. The trade-off trend between UHC and NOx emissions, as well as the CO and CO2 emissions during the combustion modes transition from HCCI to CI via PPC, are investigated and analyzed based on the fuel/wall interaction and combustion processes.