Compression Ignition Combustion Mode Research Articles

Impacts of pine oil and hydrogen induction with hemp oil methyl ester on dual fuel reactivity controlled compression ignition combustion in diesel engine

AbstractThe current research focuses on the impacts of pine oil injection and hydrogen induction separately with hemp oil methyl ester (HOME) in the single cylinder diesel engine in dual fuel‐reactivity controlled compression ignition (DF‐RCCI) combustion mode. The engine was tested under a DF‐RCCI mode for the different energy shares of 10% pine oil with HOME (10P‐HOME), 30% pine oil with HOME (30P‐HOME), 3‐lpm hydrogen with HOME (3‐lpmH2‐HOME), and 6‐lpm hydrogen with HOME (6‐lpmH2‐HOME) separately at 345 °CA bTDC of low reactivity fuel (pine oil and hydrogen) and 23°C bTDC injection timing of high reactivity fuel (HOME). The results showed a higher Brake Thermal Efficiency (BTE) of 7.44%, 5.32%, 5.72%, and 2.46% for 6‐lpmH2‐HOME, 3‐lpmH2‐HOME, 30P‐HOME, and 10P‐HOME fuel shares, respectively, over the conventional diesel combustion (CDC) at full load. 30P‐HOME, 3‐lpmH2‐HOME, and 6‐lpmH2‐HOME fuel combinations recorded 4.08% 4.42%, and 5.69% lower brake specific fuel consumption (BSFC), respectively, at full load. When comparing DF‐RCCI combustion to CDC, an increase in the heat release rate (HRR) of 2.89%–26.50% and a rise in peak cylinder pressure of 0.77%–12.99% were observed. The 30P‐HOME, 3‐lpmH2‐HOME, and 6‐lpmH2‐HOME emit less smoke in DF‐RCCI combustion mode by 13.06%, 4.84%, and 7.26%, respectively at full load condition. When using 30P‐HOME the exhaust gas temperature (EGT) decreased by 3.50% at full load condition. At part and full load conditions, the 30P‐HOME fuel share reduced oxides of nitrogen (NOX) emissions by 3.93% and 5.26%, respectively.

Study on the Effect of Two-Stage Injection Strategy for Coal-to-Liquid/Gasoline Reactivity-Controlled Compression Ignition Combustion Mode.

An experimental study was carried out on a modified single-cylinder dual-fuel engine in reactivity-controlled compression ignition (RCCI) mode using pilot fuels with different physicochemical properties, and the effects of the pilot fuels and the two-stage injection strategy on the combustion and emission characteristics of the RCCI mode were explored. The results show that when coal-to-liquid (CTL) is used with a high cetane number as the pilot fuel, the reactivity stratification of the fuel-air mixture is more pronounced. With the advancement of pilot injection timing (SOI1), the heat release rate (HRR) of the CTL/gasoline mode gradually changes from a bimodal pattern to a unimodal pattern. Among them, the bimodal HRR includes CTL premixed combustion and gasoline flame propagation, as well as CTL diffused combustion and gasoline multipoint spontaneous combustion, while the unimodal HRR represents CTL premixed combustion and gasoline multipoint spontaneous combustion. However, the HRR of the fossil diesel/gasoline RCCI combustion mode always exhibits a unimodal form. With the advancement of the main injection timing (SOI2), the gravity center of heat release (CA50) is more advanced when using CTL as the pilot fuel due to the short ignition delay. Overall, compared to fossil diesel, using CTL as the pilot fuel is conducive to controlling the pressure rise rate, which expands the operating range of the RCCI combustion mode. Besides, for both pilot fuels of CTL and fossil diesel, the advancement of SOI1 lowers particle emissions, and the advancement of SOI2 reduces NOx emissions, while the two-stage injection achieves higher indicated thermal efficiency.

Developments in the RCCI engines powered by several alternative fuel types: An overview

The perspective on internal combustion engines (ICEs) has changed because of the step-by-step decrease in oil reserves, environmental concerns, and many other reasons. However, the use of these engines will continue in the coming years. The development of ICEs has accelerated in recent years. As a result, studies on systems that can improve performance and reduce pollution in engines are carried out by many researchers. The basis of the studies carried out in this context is the change in the combustion mode. In other words, the emergence of different combustion modes is given importance by researchers. Among these, many studies have been made on the implementation of the reactivity-controlled compression ignition (RCCI) combustion mode. RCCI engine uses two different fuels. These fuels are low-reactivity (alcohol, gasoline, etc.) and high-reactivity (diesel, biodiesel, etc.) fuels. In addition, the fact that different alternative fuel types can be employed in these engines has made them popular all over the world. This review presents the results of the effects of parameters such as fuel ratio, different injection strategies, exhaust gas recirculation (EGR) rate, compression ratio, and piston geometry on the performance, emissions, and combustion behavior of RCCI engines using both conventional and alternative fuels. This study has been compiled to provide an overview of the current status of the RCCI concept and to offer benefits to researchers.

RCCI combustion of ammonia in dual fuel engine with early injection of diesel fuel

Ammonia has gained considerable attention as a valuable, carbon-free alternative fuel for internal combustion engine (ICE) applications. The growing interest in ammonia's potential as an energy source stems primarily from its advantageous storage and transport properties. The reactivity-controlled compression ignition (RCCI) combustion mode presents a promising avenue for overcoming the challenges intrinsic to conventional diesel engines, such as elevated nitrogen oxides (NOx) and particulate matter (PM) emissions. Additionally, it addresses the limitations of both homogeneous charge compression ignition (HCCI) combustion (limited operational range) and premixed charge compression ignition (PCCI) combustion (diminished power output). The application of an ammonia-based RCCI combustion strategy emerges as a viable pathway for harnessing ammonia as a fuel. In this study, a numerical simulation on a single-cylinder heavy-duty engine operated in RCCI mode is conducted utilizing ammonia and diesel as fuels. The engine is operated at medium load and 910 RPM. The simulation results are validated against experimental data sourced from existing literature. The study investigates the impact of varying ammonia energy fractions, injection timing, and intake valve close temperature (TIVC) on key operational characteristics of the engine including in-cylinder pressure, heat release rate (HRR), combustion efficiency (CE), indicated mean effective pressure (IMEP), and emission levels. The results indicated that increasing the ammonia energy fraction within the RCCI combustion mode, transitioning from 30 % to 70 %, leads to a notable enhancement in IMEP, while maintaining low levels of carbon monoxide (CO), hydrocarbons (HC), unburned ammonia, and nitrous oxide (N2O) as greenhouse gases (GHG). Furthermore, increasing ammonia's energy fraction yielded a discernible reduction in NOx emissions and carbon dioxide (CO2). Conversely, the RCCI combustion mode attained superiority over the dual fuel combustion mode by simultaneously elevating CE and diminishing emissions of GHG, (CO2 and N2O) as well as unburned NH3.

Prediction of RCCI combustion fueled with CNG and algal biodiesel to sustain efficient diesel engines using machine learning techniques

This study used microalgae biodiesel as a high-reactive fuel directly injected along with various Compressed Natural Gas (CNG) energy shares (10, 20, 30, and 40%) as low-reactive fuel injected into the intake system. The experiments are performed in a single-cylinder, water-cooled, 1500 rpm, 3.5 kW power Compression Ignition (CI) engine under various loading conditions to examine the effects of CNG energy share on performance and emissions in Reactivity Controlled Compression Ignition (RCCI) combustion mode. The study found that the 30%CNG share decreased Nitrogen oxides (NOx) and smoke by 25 and 31%, as well as an increase in thermal efficiency of 4.35% in comparison to traditional biodiesel combustion. Finally, two machine learning (ML) models, namely the Gradient Boosting Regressor (GBR) and LASSO (Least Absolute Shrinkage and Selection Operator) Regression, were developed for predicting the dependent variables individually from the independent variables. Both the LASSO and GBR models achieved high accuracy with R2 values of 0.98–0.99 and relatively low Root Mean Square Error (RMSE) values.

The effect of 1-octanol blending on the multi-stage autoignition of conventional diesel and HVO fuels

Alternative fuels can reduce the carbon intensity of diesel engine use, and a detailed understanding of the combustion process for these fuels can minimize resulting fuel consumption and emissions. 1-Octanol has been considered as an alternative diesel fuel, but little work evaluating its combustion process in detail exists. In this work, ignition of 1-octanol, both pure and in blends with conventional and renewable diesel base fuels, is analyzed in a constant volume combustion chamber and a modified Cooperative Fuels Research Octane Rating engine operating in homogeneous charge compression ignition combustion mode. 1-Octanol blending reduced the derived cetane number of either base fuel, but modest increases in chamber temperature at injection could compensate for even dramatic reductions in derived cetane number. It was further found that greater amounts of low-temperature heat release were required to reach main ignition as the 1-octanol blending volume fraction was increased in the constant volume combustion chamber. This finding is attributed to the changing local equivalence ratio, as the reacting spray diffuses further into the chamber and approaches the (lean) global equivalence ratio as the ignition delay grows. Finally, it was found that, despite lowering the derived cetane number, 1-octanol blending enhanced the reactivity of the conventional diesel fuel observed in the variable compression ratio engine. This finding is attributed to the higher rates of hydrogen abstraction from the weaker average C–H bonds in 1-octanol, as hydrogen abstraction governs intermediate temperature heat release. These findings clarify the effect of 1-octanol on physical processes and the various chemical regimes of heat release in compression ignition. The dependence of the effects of 1-octanol blending on the base fuel are emphasized, as these can inform the deployment of 1-octanol as a diesel blendstock. Application of these results can support the optimization of conventional combustion strategies for use with 1-octanol, as well as the development of 1-octanol-fueled low-temperature combustion strategies with the associated promise of very low criteria pollutant emissions.

Numerical Investigation of a Reactivity-Controlled Compression Ignition Engine Fueled with N-Heptane and Iso-Octane

In this numerical study, the effects of the premixed ratio, intake manifold pressure and intake air temperature on a four-cylinder, four-stroke, direct injection, low-compression-ratio gasoline engine, operated in reactivity-controlled compression ignition (RCCI) combustion mode at a constant engine speed of 1000 rpm, were investigated using Converge CFD software. The results of numerical analyses showed that the maximum in-cylinder pressure and heat release rate (HRR) increased and the combustion phase advanced depending on the rise in both intake manifold pressure and intake air temperature. The CA50 shifted by 18.5 °CA with an increment in the intake air temperature from 60 °C to 100 °C. It was observed that the combustion duration dropped from 44 °CA to 38 °CA upon boosting the intake manifold pressure from 103 kPa to 140 kPa. Moreover, a delay in the combustion phase occurred at a constant intake air temperature with an increasing premixed ratio. The maximum value of in-cylinder pressure was recorded as 36.15 bar (at 11 °CA aTDC) with the use of PRF20. Additionally, as the content of iso-octane in the fuel mixture was increased, combustion delay occurred, and the maximum value of in-cylinder temperature obtained was 11 °CA aTDC using PRF20 fuel at the earliest point. While HC and CO emissions reached the highest values at a 60 °C intake air temperature, NOx and soot emission values were detected at quite low levels at this temperature. The values of all these emissions increased with rising intake manifold pressure and reached their highest values at 140 kPa. In addition, while the highest HC and CO emission values were observed with the use of PRF60 fuel, the results revealed that the control of the combustion phase in the RCCI strategy is notably affected by the premixed ratio, intake manifold pressure and intake air temperature.

Co-optimization of operating parameters, fuel composition, and piston bowl geometry of gasoline compression ignition (GCI) engine at high loads

Focusing on the gasoline compression ignition (GCI) combustion mode, the operating parameters, fuel composition, and piston bowl geometry were collaboratively optimized at high loads to improve engine performance. A meliorative genetic algorithm coupled with a three-dimensional computational fluid dynamics (CFD) program was adopted as the optimization tool. The optimal GCI combustion strategy is summarized based on the optimization results, and the key parameters affecting engine performance at high loads are further analyzed. The results show that the employment of the open-type piston bowl, high-reactivity fuel, and late start of injection (SOI) is desirable for GCI engines at high loads. Under this strategy, fuel burns in multiple stages, which can reduce the heat release rate and advance the combustion phase. The width of the piston bowl is the geometric parameter with the most notable impact on GCI combustion. Due to the weaker turbulent kinetic energy and the smaller surface area, the larger piston bowl width is conducive to diminishing the heat transfer losses of the engine and promoting the oxidation of unburned hydrocarbon (HC) emissions. Relative to the optimal case, the strategy with the open-type piston bowl, high-reactivity fuel, and early SOI can reduce fuel consumption but results in a higher in-cylinder pressure rise rate and increased ringing intensity (RI). On the contrary, the re-entrant type piston bowl, low-reactivity fuel, and late SOI can significantly reduce the pressure rise rate and RI while deteriorating thermal efficiency.

Effect of n-butanol additive on the combustion and emission characteristics of a coal-derived naphtha homogeneous charge compression ignition engine under different parameters

ABSTRACT The combustion and emission characteristics of n-butanol/coal-derived naphtha blends in homogeneous charge compression ignition (HCCI) combustion mode were experimentally researched on a retrofitted diesel engine. The effects of intake temperature (T in ) and excess-air coefficient (λ) were mainly analyzed. The results show that the peak in-cylinder pressure (P max ) and peak heat release rate (HRR max ) of all tested fuels show an overall increasing trend as T in rises. The combustion gets faster and more stable, carbon monoxide (CO) and hydrocarbon (HC) emissions decrease, and the indicated thermal efficiency (ITE) first increases and then decreases. When T in remains constant, the P max and HRR max decrease and the combustion phase delays as the n-butanol volume fraction increases; CO and HC emissions gradually increase, except for that of lower T in , which shows a trend of first reduction and then increase. ITE gradually decreases in general, but when T in is higher than 100°C, coal-derived naphtha containing 24% of n-butanol in volume (B24N76) exhibits the highest ITE. In addition, for all tested fuels, both P max and HRR max decrease as λ increases and the combustion gets slower and less stable; CO and HC emissions deteriorate, and ITE gradually decreases. It is worth noting that B24N76 shows the best combustion stability for all λs and exhibits the lowest CO and HC emissions when λ are 3.0 and 3.5.

Effects of EGR on combustion and emission characteristics of PODE/methanol RCCI mode at high load

In order to extend the high-load operation range of polyoxymethylene dimethyl ethers (PODE)/methanol dual-fuel reactivity controlled compression ignition (RCCI) combustion mode, a numerical model of in-cylinder combustion was established by coupling PODE/methanol chemical reaction kinetics with CONVERGE software. And then the influence mechanism of exhaust gas recirculation (EGR) addition on in-cylinder combustion process, combustion stability and pollutant formation of the RCCI engine under high load and pilot injection strategy were investigated. The results show that with the increase of EGR ratio, the peak values of the first heat release formed by PODE pilot injection combustion and in-cylinder pressure decrease, the combustion start timing and CA50 phase are gradually delayed. While the peak value of the second heat release formed by PODE main injection combustion at low EGR ratio and the combustion duration remain unchanged. Meanwhile, as the EGR ratio increases from 0 to 30 %, the brake thermal efficiency (BTE) decreases from 46.54 % to 44.40 %. And the in-cylinder equivalent ratio and temperature field distributions become uniform, and both high-temperature region (above 1800 K) and NOx generation area are reduced, which decreases NOx emissions by 42.6 % without increasing soot emissions. The methanol mixture at squish zone is subjected to the high-temperature and high-pressure of pilot injection combustion, resulting in obvious pressure oscillation. While EGR addition decreases the generation of HCO and OH active radicals, ignition points and reaction rate, which effectively inhibits methanol spontaneous combustion and knock phenomenon, and decreases the ringing intensity from 2.82 MW/m2 to 1.50 MW/m2. The pilot injection strategy coupled with 18 % EGR can extend the indicated mean effective pressure to 1.22 MPa. However, the load further extension is mainly limited by the sharp decline of BTE.

Study on Combustion Characteristics of Diesel/Natural Gas/Hydrogen RCCI Engine

Abstract With the increasing environmental and energy problems, the development of new combustion technology has become a hot topic in the research of internal combustion engine. Reactivity controlled compression ignition (RCCI) combustion mode is the most promising combustion mode at present, which can solve the problems of combustion ignition controllability, and expand the engine load range. In this paper, optical diagnostics and numerical simulation are used to study the diesel/natural gas/hydrogen tri-fuel RCCI engine performance. Results show that hydrogen can significantly improve in-cylinder combustion and emission characteristics. With the increase of hydrogen addition, the combustion efficiency is increased accordingly, and the afterburning is prevented, which makes the exhaust energy loss decrease.

Utilization of multiwalled carbon nanotubes (MWCNT) additive in HCCI engine to widen operating range

Homogenous charge compression ignition (HCCI) combustion mode is a promising technology for the future of internal combustion engines because of its high thermal efficiency. However, HCCI engines have limited stable operating range which is a major drawback. Nanoparticles usage as fuel additive provides improvement of combustion characteristics of internal combustion engines. The objective of this study is to enlarge operating range of HCCI engine. For this purpose, the effects of multiwalled carbon nanotubes (MWCNT) on combustion characteristics of an HCCI engine were scrutinized. The effects of MWCNT on engine operating range, combustion parameters, and HC and CO emissions were determined. The maximum operating range was obtained with 75 % n-heptane, 25 % ethanol, and 100 ppm MWCNT mixture. Compared to 75 % n-heptane and 25 % ethanol mixture, 75 % n-heptane, 25 % ethanol, and 100 ppm MWCNT mixture increased the operating range of engine 112 %. Furthermore, in-cylinder pressure, heat release rate, indicated thermal efficiency, and maximum pressure rise rate were increased with use of MWCNT additive. Start of combustion and 50 % heat release location was shifted to earlier crank angles. Combustion duration was shortened. HC and CO emissions were also decreased.

Experimental studies on premixed charge and reactivity-controlled compression ignition combustion modes using gasoline/diesel fuel combination

Homogeneous charge compression ignition (HCCI) is a promising technology to reduce NOx and soot emissions in compression ignition (CI) engines. However, this technology lacks combustion control to circumvent the knocking and misfire limitations. Premixed charge compression ignition (PCCI) and reactivity-controlled compression ignition (RCCI) are techniques that use partial homogeneous charge to reduce NOx and soot emissions. Here, combustion is regulated either by controlling the injection timing or fuel reactivity. PCCI uses a part of fuel as premixed to form a partially homogeneous charge and the rest as direct-injected. RCCI, on the other hand, uses a low reactive fuel (LRF) for port injection to form a partially homogeneous charge and a high reactive fuel (HRF) for direct injection. In this work, we studied PCCI and RCCI modes using commercially available fuels like diesel and gasoline, and we compared the results with diesel baseline operation. Adding 40% (by weight) heated diesel port injection to normal diesel operation in PCCI mode at different loads showed a minimum reduction in NOx and smoke emissions by 15% and 6%, respectively, when compared with diesel baseline. This mode was found to be equally efficient with diesel baseline operation at low torque conditions. Similarly, adding 40% (by weight) of gasoline port injection to normal diesel operation in RCCI mode at different loads showed a minimum reduction in NOx and smoke emissions by 20% and 14%, respectively, when compared with diesel baseline. This mode was found to be equally efficient with diesel baseline operation at high torque conditions.

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

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

Effects of research octane number of gasoline and dual direct injection strategies on combustion and emission performance of intelligent charge compression ignition (ICCI) mode

Dual-fuel intelligent charge compression ignition (ICCI) combustion mode has been proved to be an efficient combustion mode for internal combustion engines. The properties of low reactivity fuel have a strong influence on ICCI combustion. In this paper, based on a modified ICCI engine, the effect of octane number of low reactivity fuels on ICCI combustion mode was studied under medium engine load, in which 75#, 80#, 85#, and 95# gasoline were applied as low reactivity fuels. In addition, dual-fuel injection strategies were tested and optimized. Results showed that ICCI mode performed well with gasoline research octane numbers (RON) even low as to 75. With the decrease of gasoline RON, the reactivity of mixture increased which caused the advanced combustion. This also made the peaks of heat release rate and in-cylinder pressure advance with the decrease of RON. By post-injection strategy of gasoline and diesel, the combustion phase could be delayed when fueled with low-octane fuel but significantly increased the particle number to 109/cm3. Under the respective optimized fuel injection strategies, 85# gasoline achieved ultra-low NOx emission (0.15 g/kWh), low particle numbers (under 107/cm3), and high indicated thermal efficiency (close to 50%).

Experimental investigation on operating light-duty diesel engine using ethanol–gasoline blends in a homogeneous charge compression ignition combustion mode

The advanced diesel combustion mode of homogeneous charge compression ignition (HCCI) provides simultaneous lessening of soot and oxides of nitrogen (NOx) emissions. However, HCCI operations with low volatility and high reactivity diesel fuel require energy-intensive vaporizers and suffer from a restricted operating load range. In this work, high volatility, and low reactivity ethanol–gasoline blends were utilized as fuels in a port fuel injected light-duty diesel engine operated in HCCI mode to address this limitation. To study the effect of adding ethanol to the test fuels, its content was progressively increased from 10% to 60% by simultaneously reducing the gasoline content. 6% of an ignition improver, 2-ethylhexyl nitrate (2-EHN), was added to test fuels to attain stable HCCI combustion in the test engine at lower engine loads. A combined experimental and statistical approach was followed to characterize the HCCI engine combustion, performance and emissions. The impact of independent operating factors of ethanol–gasoline fuel blend composition and engine load on the various response parameters was estimated using multi-regression models developed based on the response surface method (RSM). The optimization of engine parameters was performed using the desirability approach of RSM to maximize performance and minimize emissions. The engine operating load range was extended from 23% (1.22 bar BMEP) to 86% (4.63 bar BMEP) with ethanol–gasoline–2-EHN-fuelled HCCI, which was a substantial improvement over the achievable load range only up to 38% (2.02 bar BMEP) with diesel-fuelled HCCI. All the multi-regression models developed were statistically significant at a 95% confidence level. The results showed that the indicated thermal efficiency improved, and soot and NOx emissions reduced with increased ethanol content in the test fuels. The test engine showed optimal working conditions when operated using 49% ethanol in the test fuels at 75% engine load. To benchmark the HCCI engine performance under optimal operating conditions, it was compared with conventional diesel combustion at 75% engine load. The NOx and soot emissions decreased by 76% and 98%, respectively, while indicated thermal efficiency increased by 20% for HCCI than conventional mode. The optimal fuel reactivity was determined at various engine loads by using the model equation developed for combustion phasing. According to the findings of this study, the fuel management strategy of using ethanol and gasoline blends is a viable method to enhance the performance and emission metrics of HCCI engines.

Effects of EGR combined with DOC on emission characteristics of a two-stage injected Fischer-Tropsch diesel/methanol dual-fuel engine

Fischer-Tropsch (F-T) diesel and methanol are widely regarded as promising clean alternative fuels for engines. The emergence of reactivity controlled compression ignition (RCCI) combustion mode provides new approaches to the application of F-T diesel and methanol in diesel engines, but there is a pressing need to further reduce engine emissions. To this end, a dual-fuel engine test bench was built based on a high-pressure common rail diesel engine with a methanol injection system at the intake manifold combined with a two-stage in-cylinder direct injection (pre-injection + main injection) F-T diesel. The combined effects of methanol substitution ratio (MSR), exhaust gas recirculation (EGR) and diesel oxidation catalyst (DOC) on the combustion and emission characteristics of the dual-fuel engine was investigated at 2000 rpm and 75 % load. The results show that EGR improves the combustion characteristics of the F-T diesel/methanol dual-fuel engine while adding a DOC significantly reduces engine gaseous emissions. However, as the MSR and EGR rate increase, NOx emissions decrease, but other emissions increase. NOx emissions were reduced by 73 % compared to the original engine emissions for an MSR of 30 % and an EGR rate of 15 % without a DOC. When the MSR is 0 %, the DOC promotes the conversion of NO to NO2. While, when the MSR greater than 0, the DOC promotes the conversion of NO2 to NO. When equipped with a DOC, CO, NO, NO2, NOx, MeOH, and HCHO emissions decrease as the EGR rate increases, with the reduction of CO and MeOH emissions being greater than 99.5 % and 93 %, respectively, and the maximum conversion efficiency for HCHO emissions being 82 %. The present study showcases the key challenges as well as advantages in the use of EGR combined with a DOC assisting the application of coal-based alternative fuels in dual-fuel engines.

Products of catalytic oxidative coupling of methane to improve thermal efficiency in natural gas engines

Pretreating natural gas using catalytic oxidative coupling of methane (OCM) produces ethylene and ethane, both species that increase fuel reactivity, thus increasing the potential to expand the operability range of highly efficient compression ignition combustion in natural gas engines. This paper presents the first experimental results on the impact of OCM product species on engine thermal efficiency and operability range. In the work, a benchtop experiment was conducted to generate a product species distribution from OCM over a Sr/La2O3 catalyst. A computational study using known chemical mechanisms was then employed to investigate the laminar flame speed and ignition delay of the OCM-modified fuel. Finally, engine experiments in both spark-ignition and compression-ignition combustion modes were carried out using a variable compression ratio single-cylinder engine. Results from the benchtop catalyst experiments showed that practical fuel conversion for single-pass OCM resulted in 18 % methane conversion, 60 % C2 selectivity, and 10.8 % C2 yield at a molar C/O ratio of 6. After determining realistic fuel blending ratios for engine operation, the numerical simulation results showed that fuel reactivity and ignition delay improved compared to with methane alone, while laminar flame speed decreased due to higher dilution from the presence of inert OCM products. Engine experimental results confirmed that OCM products have an advantage in CI mode due to reduced ignition delay time. The CI operating range was widely expanded, and approximately 9.9% thermal efficiency gain was achieved. By contrast, efficiency in SI mode was reduced when using OCM products due to an increase in combustion duration and retarded combustion phasing.

Exergy analysis in a HCCI engine operated with diethyl ether-fusel oil blends

Homogeneous Charge compression ignition (HCCI) combustion mode is a very interesting new combustion model with high efficiency, low nitrogen oxide (NOx), and soot emissions. In the present investigation, the performance of an HCCI engine operated with three fuel ratios, i.e., 40% diethyl ether and 60% fusel oil (D40F60), 60% diethyl ether and 40% fusel oil (D60F40), and 80% diethyl ether and 20% fusel oil (D80F20), at different lambda values and engine speeds was assessed from exergy indicators. The results indicate that the lambda variation allows observing the best performance zones when operating with fuel blends. From the comparison of the exergy indicators, it is concluded that the highest engine efficiency is obtained when operating with D40F60 at a lambda between 2.1 and 2.2. However, it was determined that the increase of diethyl ether in the blend decreases the HCCI engine performance. Also, greater stability of performance was recorded when operating with D80F20. A higher exergy destruction rate is observed between lambda 3.4 and 3.9 when operating with D80F20. The exergetic efficiency values varied from 5.34% to 23.85%. According to the results obtained, the lowest and highest value of exergy efficiency was recorded for the D80F20 and D40F60, respectively.

Detailed Analysis of the Effects of Biodiesel Fraction Increase on the Combustion Stability and Characteristics of a Reactivity-Controlled Compression Ignition Diesel-Biodiesel/Natural Gas Engine

A single-cylinder marine diesel engine was modified to be operated in reactivity controlled compression ignition (RCCI) combustion mode. The engine fueling system was upgraded to a common rail fuel injection system. Natural gas (NG) was used as port fuel injection, and a diesel/sunflower methyl ester biodiesel mixture was used for direct fuel injection. The fraction of biodiesel in the direct fuel injection was changed from 0% (B0; 0% biodiesel and 100% diesel) to 5% (B5) and 20% (B20) while keeping the total energy input into the engine constant. The objective was to understand the impacts of the increased biodiesel fraction on the combustion characteristics and stability, emissions, and knocking/misfiring behavior, keeping all other influential parameters constant. The results showed that nitrogen oxides (NOx) emissions of B5 and B20 without the need for any after-treatment devices were lower than the NOx emission limit of the Euro VI stationary engine regulation. B5 and B20 NOx emissions decreased by more than 70% compared to the baseline. Significantly more unburned hydrocarbons (UHCs) and carbon monoxide (CO) emissions were produced when biodiesel was used in the direct fuel injection (DFI). The results also showed that using B5 and B20 instead of B0 led to an increase of 18% and 13.5% in UHCs and an increase of 88.5% and 97% in CO emissions, respectively. Increasing the biodiesel fraction to B5 and B20 reduced the maximum in-cylinder pressure by 3% and 10.2%, respectively, compared to B0. Combustion instability is characterized by the coefficient of variation (COV) of the indicated mean effective pressure (IMEP), which was measured as 4.2% for B5 and 4.8% for B20 compared to 1.8% for B0. Therefore, using B20 and B5 resulted in up to 34.9% combustion instabilities, and 18.5% compared to the baseline case. The tendency for knocking decreased from 13.7% for B0 to 4.3% for B20. The baseline case (B0) had no misfiring cycle. The B5 case had some misfiring cycles, but no knocking cycle was observed. Moreover, the historical cyclic analysis showed more data dispersions when the biodiesel fraction increased in DFI. This study shows the potential of biodiesel replacement in NG/diesel RCCI combustion engines. This study shows that biodiesel can be used to effectively reduce NOx emissions and the knocking intensity of RCCI combustion. However, combustion instability needs to be monitored.