Indicated Thermal Efficiency Research Articles

Effects of Post-Injection Characteristics on the Combustion, Emission, and Performance in a Diesel-Syngas Reactivity Controlled Compression Ignition Engine

This paper presents a numerical investigation of the separate effects of post-injection characteristics in a heavy-duty turbocharged direct injection diesel engine under pure diesel combustion (PDC) and diesel-syngas combustion (DSC) operating conditions. Converge CFD code was used coupled with a detailed n-heptane/toluene/PAH chemical kinetic mechanism (consists of 71 species and 360 reactions) for diesel-syngas dual-fuel combustion simulation. A total of 36 strategies based on the post-injection characteristics (post-injection timing, fuel quantity, spraying pressure, and main-post dwell time) on the combustion characteristics, exhaust gas emissions, and engine performance under PDC and DSC conditions were investigated. Numerical achievements revealed that 40% substitution of diesel fuel with syngas significantly decreased particulate matter emission and enhanced the indicated thermal efficiency (ITE), compared to the baseline PDC case. However, carbon monoxide noticeably increased. In addition, retarding the post-injection timing prolonged the combustion duration and also reduced the nitrogen oxides emissions and ITE. By increasing the post-injection quantity up to 15%, the combustion process deteriorated, and carbon-based emissions such as particulate matter, carbon monoxide, and unburnt hydro-carbon in the exhaust gases increased under PDC and DSC conditions. Furthermore, increasing post-injection pressure (PIP) from 1000 to 1450 bar under both PDC and DSC conditions led to higher flame temperature, and as a result, the heat release rate peak point and temperature peak point for the second combustion event increased. However, at a PIP of 1600 bar, the ITE deteriorated under PDC and DSC operating cases.

Auto-ignition of polyoxymethylene dimethyl ether 3 (PODE3) blended with diesel and gasoline via combustion under homogeneous charge compression ignition

• PODE 3 /diesel/gasoline blends in a HCCI engine are studied for the first time. • High temperature kinetic reactions are dependent on cetane number of fuel blend. • Oxygen from PODE 3 helps promote better ignition when gasoline is added to PODE 3 . • Gasoline addition to PODE 3 presents higher efficiency than diesel addition. • PODE 3 demonstrates high potential in encouraging clean combustion. With high oxygen content and cetane number, PODE 3 is a favorable renewable fuel for engines. PODE 3 /diesel/gasoline blends in a HCCI engine are numerically studied for the first time. The effects of fuel blend ratio and equivalence ratio (ER) on auto-ignition are investigated. A highly compact and robust chemical mechanism has been implemented. Crank angle at which 50 percent of heat is released (CA50) displays higher sensitivity towards blend ratio in leaner mixtures with 50% PODE 3 displaying a change of 12.31 CAD at 0.34 ER and only 6.19 CAD at 0.5 ER when made in comparison to their respective CA50 at 100% PODE 3 . Furthermore, indicated thermal efficiency (ITE) is observed to be better with higher ER with 100% PODE 3 having a 23.3% increase in ITE at 0.5 ER than at 0.34 ER, and is generally higher with increased PODE 3 . Neat PODE 3 displays lowest CO and highest CO 2 for all cases, manifesting high oxidation reactivity. Additionally, acetylene levels are substantially lower for combustions at 0.5 ER as compared to 0.34 ER. Lastly, PODE 3 yields only 2.04 × 10 −10 g/cycle and 5.67 × 10 −11 g/cycle of C 2 H 2 at 0.34 ER and 0.5 ER respectively. With nearly no soot precursors, PODE 3 demonstrates high potential in encouraging clean combustion.

Comparative evaluation of the combustion process and emissions of a diesel engine operating on the cetane improver 2-Ethylhexyl nitrate doped rapeseed oil and aviation JP-8 fuel

• Diesel engine tested with rapeseed oil (RO) and jet fuel (JF) at 1400 and 2200 rpm. • 2-EHN is more active in reducing the ignition delay of JF rather than RO at both rpm. • MBF 50 and MBF 90 are smaller, but the ITE is a bit lower with the doped JF-24 fuel. • NO x is 49% higher, but smoke 27% lower with doped RO-30 than with JF-24 at 2200 rpm. • The combustion of JF-fuel-sets emits THC less than RO-sets at a speed of 2200 rpm. Rapeseed oil (RO) and JP-8 fuel (JF) as alternatives could be used as diesel fuel supplements in many power sectors however, the low cetane number related drawbacks should be removed to overcome the difficulties in the ignition and to achieve efficient-clean combustion of the fuels. The purpose of the research is to make a comparative evaluation of the cetane enhancer-made effects on the combustion process, cyclic variability, thermal efficiency, smoke, and exhaust emissions. At first, a naturally aspirated engine operated with the undoped RO and JF to identify the baseline parameters for full (100%) loads corresponding to Indicated Mean Effective Pressures (IMEP) of 0.844 and 0.738 MPa at speeds of 1400 and 2200 rpm. Then, the engine operated with the 2-EHN doped fuels 0.10 (RO-10), 0.30 (RO-30) and 10 (JF-10), 24 vol% (JF-24) to get new results needed for comparative evaluation of the benefits and detriments in the combustion process, engine efficiency, smoke, and emissions. The ignition delay was 10.3% and 44.6% shorter, the Indicated Thermal Efficiency (ITE) was 6.1% higher and 1.2% lower, the NO x emissions were a little and 10.3% lower with the doped RO-30 and JF-24 at a speed of 2200 rpm. The coefficients of cyclic variations (COVs) of the IMEP were 9.7% higher and 11.8% lower, the in-cylinder maximum pressure was 22.5% and 29.0% lower, and the increment rate of maximum pressure was 13.5% and 14.9% lower, respectively. Also, RO-30, JF-24 fuels suggested smoke opacity and CO emissions 42.1%, 32.1% and 11.6%, 2.7% higher, THC emissions 1.9 times higher, and 28.6% lower for engine tested conditions.

OBSERVATIONAL ANALYSIS ON RESULT OF YSZ COATED PISTON CROWN ON THE BEHAVIOUR OF A PETROL ENGINE

An observational study of thermal barrier coating (TBC) on the working of 4-stroke single cylinder petrol engine was studied. Yttria Stabilized Zirconia (YSZ) used as coating material. YSZ has less thermal conductivity, sustainability under high temperature and pressure. Main aim of TBC is to decrease heat losses to the cooling jacket of the engine. YSZ is coated on the piston crown by Plasma spray method. YSZ coating improves the performance of petrol engine. Experimental study was carried out on 4-stroke single cylinder OHV petrol engine 25‎°C inclined cylinder horizontal shaft engine on performance of ceramic coated engine and compared with baseline engine under different speed. Results show that ceramic coated engine is more effective than conventional engine as brake specific fuel consumption (BSFC) is reduced 2-4% than normal piston engine, brake thermal efficiency (BTE) of modified engine is expanded 4-8% than unmodified engine. Indicated thermal efficiency (ITE) of modified piston engine is increased 5-10% than normal engine. Mechanical efficiency (ME) of the TBC engine is increased 4-10% than standard engine. Volumetric efficiency (VE) of modified engine is decreased 3-9% when compared with standard engine and exhaust gas temperature (EGT) of ceramic coated engine is increased 1-3% than unmodified engine. KEYWORDS: Petrol Engine, Thermal barrier coating (TBC), Yttria Stabilized Zirconia (YSZ). Mechanical Efficiency

Study of water direct injection on knock control and combustion process of a high compression ratio GDI engine

To improve the engine thermal efficiency and reduce emissions, a single-cylinder gasoline direct injection (GDI) engine was installed with a water direct injection (WDI) system in the current research. The effects of water injection ratio (WIR) and water injection timing (WIT) on engine combustion, knock intensity, and emissions were studied. The maximum braking torques (MBT), and the corresponding spark timings (ST) with different WDI strategies were investigated. The results showed that the WDI could effectively inhibit engine knock through increased WIR or delayed WIT, while the indicated thermal efficiency (ITE) was reduced. With increasing WIR, the decreased in-cylinder temperature led to reduced NOx emission but increased HC emission. CO emission gradually decreased but increased again when WIR was over 40%. With WIR of 50% at test basic ST and MBT, NOx emission reduced by 48% and 18.8%, HC emission increased by 7.3% and 36.1%​​, but the ITE decreased by 1.3% and increased by 3% respectively. With the delay of WIT at test basic ST conditions, ITE and the emissions of NOx, CO, and HC decreased, CA50 gradually retarded, the exhaust temperature steadily increased. IMEP increased by 9.5%, and ITE increased by 3.5% at WIT of −60°CA ATDC when ST was optimized to MBT. NOx emission of basic ST and MBT decreased by 34.4% and 11.5% compared with the basic conditions, respectively. The optimized trade-off between ITE and emission was achieved with the WIT of −100°CA ATDC and WIR of 50%. The ITE and IMEP under WDI conditions can be further improved at the sacrifice of emissions with the optimized earlier combustion phase, but the increased range depended on knock suppression. The correlation between WIR and knock was more significant than that of WIT, indicating more robust knock suppression.

Computational optimization of CH4/H2/CO blends in a spark-ignition engine using quasi-dimensional combustion model

Recent research has proven that computational fluid dynamics (CFD) modeling in combination with a genetic algorithm (GA) algorithm is an effective methodology to optimize the design of internal combustion (IC) engines. However, this approach is time consuming, which limits the practical application of it. This study addresses this issue by using a quasi-dimensional (QD) model in combination with a GA to find optimal fuel composition in a spark ignition (SI) engine operated with CH4/H2/CO fuel blends. The QD model for the simulation of combustion of the fuel blends coupled with a chemical kinetics tool for ignition chemistry was validated with respect to measured pressure traces and NOx emissions of a small size single-cylinder SI engine operated with CH4/H2 blends. Calibration was carried out to assess the predictive capability of the QD model, and the effect of hydrogen addition on the lean limit extension of the methane fueled engine was studied. A GA approach was then used to optimize the blend composition and engine input parameters based on a fitness function. The QD-GA methodology was implemented to simultaneously investigate the effects of three input parameters, i.e., fuel composition, air–fuel equivalence ratio and spark timing on NOxemissions and indicated thermal efficiency (ITE) for the engine. The results found indicated that this approach could provide optimal fuel blends and operating conditions with considerable lower NOx emissions together with improved thermal efficiencies compared to the methane fueled engine. The presented computationally-efficient methodology can also be used for other fuel blends and engine configurations.

Comparative assessment of n-butanol addition in CTL on performance and exhaust emissions of a CI engine

Coal to liquid (CTL) is a diesel alternative fuel based on Fischer-Tropsch (FT) process, which has shown promising application value. Besides, as an oxygenated biofuel with high oxygen content and volatility, n-butanol can be blended with hydrocarbon fuels to improve engine performance. This study aims to investigate the effects of CTL/n-butanol blends on the performance of the compression-ignition (CI) engine, and to reveal the influence of combustion boundary conditions such as n-butanol blending ratio, the start of injection (SOI), and exhaust gas recirculation (EGR) on the combustion and emissions characteristics. The results show that blending n-butanol with CTL is beneficial to improve the fuel-gas mixture distribution in the cylinder, and the premixed combustion ratio (PCR) increases by 13.66% as the energy ratio of n-butanol increases to 30% (B30) compared with the pure CTL. CTL/n-butanol blends make particulate emission tend to be shifted towards nucleation mode and the particulate mass emission significantly reduced, especially the particulate mass of B30 reduce by 68.6%; meanwhile, the NOx emission shows an upward trend. Compared with n-butanol blended, adjusting the SOI impacts NOx emissions significantly, while its influence on the indicated thermal efficiency (ITE) and particulate emissions is relatively slight. Moreover, through the synergistic control of n-butanol addition and EGR, the trade-off relationship between NOx and particles is mitigated.

Effects of Intake Components on Combustion and Emission Characteristics in an n-Butanol/Diesel Blend Fueled Engine.

To assess the effects of intake components and n-butanol application on compression-ignition engines, an experiment was carried out based on a single-cylinder engine fueled with n-butanol/diesel-blended fuel. The results show that with the increased n-butanol fraction of the blended fuel, the emissions of particulate mass (PM) decrease significantly, but the NOx and hydrocarbon (HC) emissions deteriorate. For B15 and B30, the PM emissions are 66.2% and 74.4% lower than B0, respectively. Furthermore, exhaust gas recirculation (EGR) was introduced to reduce the NOx emissions. However, a large EGR rate significantly reduces the indicated thermal efficiency (ITE) of the engine. Compared with the non-EGR condition, the ITE of B15 and B30 decrease by 3.1% and 3.8%, respectively, when the EGR rate is 18%. At the same time, the PM and HC emissions are found to be increased greatly. The PM emission of B15 and B30 increases by 69% and 46% and the HC emission increase by 150% and 71%, respectively. To restrain the engine emissions caused by the EGR, pure oxygen is further introduced into the intake charge. It is found that both the PM and HC emissions are significantly reduced with the introduction of extra oxygen. Under the condition of the 18% EGR rate, increasing oxygen addition to 4% can reduce HC emissions by more than 50% and the total particle mass of B15 and B30 is reduced by 60.6% and 47.7%, respectively. Moreover, the ITE reduction and combustion deterioration caused by the large EGR are found to be alleviated. By adjusting the n-butanol ratio, EGR rate, and oxygen addition, the excellent performance of combustion and emission can be achieved in an n-butanol/diesel blend fueled engine.

Effect of pre-main-post diesel injection strategy on greenhouse gas and nitrogen oxide emissions of natural gas/diesel dual-fuel engine at high load conditions

Natural gas/diesel dual-fuel (NDDF) engine technology is an interesting concept for decreasing greenhouse gas (GHG) emissions of heavy-duty diesel engines. One of the main limitations of this concept is the emissions of unburned methane which is estimated to have a GHG potential factor of 25 – 34 over a 100-year period. Our previous study has shown that a NDDF engine using pre-main-post diesel injection strategy can reduce unburned methane emissions, but yields lower indicated thermal efficiency (ITE) and higher carbon dioxide (CO2) and nitrogen oxides (NOx) emissions compared to that using single diesel injection strategy under high engine load conditions due to the advanced combustion phasing. In this study, the combustion phasing of pre-main-post diesel injection strategy is further optimized with the goal to improve the ITE and reduce the GHG and NOx emissions without compromising the unburned methane emissions when compared to single injection strategy. The results reveal that changing pre diesel injection timing gives more controllability of the combustion phasing than changing the main and post diesel injection timing. A more homogenous premixed mixture of pre injected diesel – natural gas – air retards the combustion phasing which allowed further improvement of the ITE and GHG emissions of NDDF engines while maintaining the low unburned methane emissions feature of the pre-main-post injection strategy. It is found that the optimized pre-main-post diesel injection strategy is able to reduce unburned methane, GHG, and NOx emissions by 13.4%, 1.5%, and 42%, respectively, and increase ITE by 0.37% compared to single injection strategy.

Performance and emissions of natural gas/diesel dual-fuel engine at low load conditions: Effect of natural gas split injection strategy

The combination of diesel and natural gas fuels has superior performance in terms of nitrogen oxides (NOx) and particulate matter (PM) emissions when compared to conventional diesel engine. However, this advantage does not hold at low load operating conditions as indicated thermal efficiency (ITE), carbon monoxides (CO), and unburned hydrocarbon (HC) emissions deteriorate. Most published studies tried to resolve this drawback using diesel split injection. However, the present study evaluates natural gas split injection strategy as an alternative to improve the performance and emissions of diesel/natural gas dual-fuel engines at low load conditions. The results show that natural gas split injection with proportional split injection ratio (ISR) and small dwelling timing improves NOx, CO, and HC emissions. Moreover, split injection of natural gas with proportional ISR after intake valve closing (IVC) is found to improve SFC, ITE, and power. Conversely, natural gas split injection strategy with proportional ISR after intake valve opening (IVO) yields poor engine performance. Overall, split injection of natural gas with low ISR yields the greatest engine performance at long dwelling time, whereas it worsens emissions compared to single injection of natural gas at 560°CA ATDC, which serves as the baseline condition. However, very low CO and HC emissions of natural gas split injection is achieved at low ISR and short dwelling time. Finally, this study reveals also that stratification of air/natural gas mixture due to natural gas split injection strategy can significantly improve the performance and emissions of dual-fuel diesel/natural gas engine at low load conditions.

Comparative assessment of stoichiometric and lean combustion modes in boosted spark-ignition engine fueled with syngas

Synthesis gas (syngas) is considered an intermediate step between conventional carbon-based fuels and future hydrogen-based fuels. Spark-ignition (SI) engines are suitable for converting the chemical energy of syngas for small-scale electrical power generation. However, syngas-fueled SI engines have lower power outputs and thermal efficiencies than SI engines fueled with conventional fuels such as gasoline and natural gas do. The objective of this study was to compare the stoichiometric and lean combustion modes in a single-cylinder SI engine to determine the optimal combustion mode for the development of a syngas engine generator with high power and high efficiency. A high gross indicate power was achieved in the stoichiometric combustion mode by increasing the intake pressure, owing to the increase in the volumetric efficiency and syngas fuel input. The gross indicated thermal efficiency (ITE) improved as the compression ratio was increased from 10:1 to 17.1:1, owing to the high peak heat release rate and short combustion duration. In the lean combustion mode, high gross ITEs were achieved by increasing the excess air ratio to 2.5, but the additional increase led to low combustion efficiencies. However, the gross indicated power decreased with an increase in the excess air ratio. The low gross indicated power was increased through intake boosting. Based on a parametric study, the optimal compression ratio for the stoichiometric combustion mode was selected to be 15:1. Pre-ignition occurred in the stoichiometric combustion mode at a compression ratio of 17.1:1 and an intake pressure of 0.16 MPa. Engine operation with a high compression ratio of 17.1:1 was possible in the lean combustion mode owing to the low combustion temperature. The gross ITE in the lean combustion mode was 18.4% higher than that in the stoichiometric combustion mode, mainly because of a significant reduction in the heat transfer loss. However, the gross indicated power in the lean combustion mode was 25.6% lower than that in the stoichiometric combustion mode.

Potential of reactivity-controlled compression ignition with reverse reactivity stratification (R-RCCI) fueled with gasoline and polyoxymethylene dimethyl ethers (PODEn)

To improve the trade-off between thermal efficiency and peak heat release rate (HRR) of partially premixed combustion (PPC) and the combustion efficiency of reactivity-controlled compression ignition (RCCI), the combustion mode with premixed high-reactivity fuel and direct-injection (DI) low-reactivity fuel, called RCCI with reverse reactivity stratification (R-RCCI), was explored at low loads in a light-duty diesel engine in this study. Compared with diesel, polyoxymethylene dimethyl ethers (PODEn) has better volatility, which is beneficial for the formation of premixed charge, so it was used as the premixed high-reactivity fuel for R-RCCI in this work. The gasoline and P20G80 (PODEn/gasoline blends with the volume fraction of 20%/80%) were respectively applied as the DI low-reactivity fuel. By investigating the combustion characteristics of R-RCCI, it is found that R-RCCI can break the trade-off between combustion efficiency and nitrogen oxides (NOx) emissions. This is because the combustion efficiency of R-RCCI is dominated by the spray location of the DI fuel rather than the 50% burn point (CA50). As the start of injection (SOI) timing is retarded, the fuel injected within the piston bowl increases, and combustion efficiency, as well as indicated thermal efficiency (ITE), is considerably promoted. Meanwhile, CA50 progressively retards with delayed SOI timing, which effectively reduces NOx emissions. The soot emissions of R-RCCI are also extremely low. The maximum ITE of PODEn/P20G80 R-RCCI is significantly higher than that of PODEn/gasoline R-RCCI. This occurs because the higher reactivity of P20G80 can reduce the sensitivity of CA50 to SOI timing and improve combustion stability, so a more delayed SOI timing is allowed to improve ITE. With the same engine configurations, R-RCCI can reduce peak pressure rise rate and improve combustion stability, while enhancing combustion efficiency and ITE compared with RCCI at the low-load conditions tested in this study.

A comparative study on the performance of partially premixed combustion (PPC), reactivity-controlled compression ignition (RCCI), and RCCI with reverse reactivity stratification (R-RCCI) fueled with gasoline and polyoxymethylene dimethyl ethers (PODEn)

To solve the challenges of the high heat release rate of partially premixed combustion (PPC) and low combustion efficiency of reactivity-controlled compression ignition (RCCI), RCCI with reverse reactivity stratification (R-RCCI) fueled with gasoline and polyoxymethylene dimethyl ethers (PODEn) was investigated at low and medium loads in a light-duty compression-ignition engine in this study. The results indicated that R-RCCI has moderate combustion rate and combustion efficiency between PPC and RCCI. At both low and medium loads, R-RCCI has the highest indicated thermal efficiency (ITE) due to its relatively lower heat transfer losses compared with PPC. Moreover, the nitrogen oxides (NOx) and soot emissions of R-RCCI are significantly lower than that of PPC. Although RCCI has the lowest heat transfer losses, its considerably low combustion rate leads to substantial exhaust losses and thereby yields a low ITE. Compared with RCCI, R-RCCI has a better balance between the degree of premixed combustion and combustion temperature, which is crucial for soot oxidation, so it has very low soot emissions at both low and medium loads.

The combustion and emission characteristics of diesel-ethanol blends with THF as cosolvents in a diesel engine operating with EGR

Tetrahydrofuran (THF) is not only an excellent co-solvent for ethanol but also a promising clean oxygen-containing fuel. The objective of the diesel engine test is to reveal the effects of exhaust gas recirculation (EGR) rates and THF as co-solvents between ethanol and diesel on the combustion and emissions. Results show that the maximum rate of pressure rise increases with the growth of the additive proportion of ethanol or THF under low EGR rates. The indicated thermal efficiency (ITE) of mixedfuels is slightly higher than that of neat diesel fuel when the EGR rate is below 30%. With the increase of THF and ethanol fraction, carbon monoxide (CO) and soot emissions of blends decrease greatly, while total hydrocarbons (THC) emissions gradually increase, especially under medium and high EGR rates. Finally, E30T10 fuel (30% ethanol, 10% THF, and 60% diesel by vol.) presents ultra-low soot emissions under all EGR rates and breaks the conventional trade-off between soot and nitrogen oxides (NOx). Under medium EGR rates, NOx emissions of E30T10 are reduced markedly, but THC and CO emissions are still at low levels. Meanwhile, the ITE of E30T10 still maintains a high level.

Parametric investigation on hydrogen driven homogeneous charge compression ignition mode with advanced diesel injection using chemical kinetics based numerical model

In the present study, a numerical model based on chemical kinetics was developed to investigate the effect of different parameters on characteristics of hydrogen diesel homogeneous charge compression ignition (HDHCCI) mode. The results showed that the combustion process was retarded with diminished cool flame as increasing hydrogen energy share (HES) due to reduction of H2O2, H2O and OH radicals with hydrogen addition. Thus, it increased the indicated thermal efficiency (ITE) and decreased the indicated specific energy consumption (ISEC). The levels of NOx and soot emissions were reduced by 22% and 63% at maximum HES. A spray angle of 10° decreased the total fuel impingement compared with a spray angle of 74° because of improvement in air-fuel mixing phenomena. Incomplete combustion was recovered at HES of 25% when increasing the charge temperature or adapting the twin-pulse in HDHCCI mode, consequently the ITE was improved with a decrease in ISEC.

Experimental study on tri-fuel combustion using premixed methane-hydrogen mixtures ignited by a diesel pilot

A comprehensive investigation on diesel pilot spray ignited methane-hydrogen (CH4–H2) combustion, tri-fuel combustion (TF), is performed in a single-cylinder compression ignition (CI) engine. The experiments provide a detailed analysis of the effect of H2 concentration (based on mole fraction, MH2) and charge-air temperature (Tair) on the ignition behavior, combustion stability, cycle-to-cycle (CCV) and engine performance. The results indicate that adding H2 from 0 to 60% shortens the ignition delay time (IDT) and combustion duration (based on CA90) up to 33% and 45%, respectively. Thereby, H2 helps to increase the indicated thermal efficiency (ITE) by as much as 10%. Furthermore, to gain an insight into the combustion stability and CCV, the short-time Fourier transform (STFT) and continuous wavelet transform (CWT) methodologies are applied to estimate the combustion stability and CCV of the TF combustion process. The results reveal that the pressure oscillation can be reduced up to 4 dB/Hz and the CCV by 50% when MH2 < 60% and Tair < 55 °C. However, when MH2 > 60% and Tair > 40 °C, abnormal combustion and knocking are observed.

A Theoretical Investigation on the Performance and Combustion Parameters in an Spark Ignition Engine Fueled With Different Shale Gas Mixtures

Abstract In this paper, a zero-dimensional (0D) single-zone combustion model was applied for predicting combustion and indicated engine parameters in a spark ignition (SI) engine. Three different shale gas mixtures, methane, and liquefied petroleum gas (LPG) (30% C3H8–70% C4H10), were studied as SI engine fuel. The shale gas compositions included shale gas-1 (86% CH4–14% C2H6), shale gas-2 (81% CH4–10% C2H6–9% N2), and shale gas-3 (58% CH4–20% C2H6–2% C3H8–10% CO2). Experimental results of the SI engine operated with LPG were used in the model verification phase and provided to the validation of the theoretical model. In addition, the operational parameters of the LPG engine were used as the model input values. The results show that shale gas-1 has the potential to be a good alternative fuel to LPG for SI engines. Shale gas-1 has an indicated mean effective pressure (IMEP) value of 5.7–7.3%, which is lower than LPG in the range of ϕ = 0.83–1.2. Furthermore, LPG has a 27.7% higher indicated specific fuel consumption (ISFC) compared to shale gas-1. On the other hand, LPG has 1.2–2.4 units lower indicated thermal efficiency (ITE) values than shale gas-1 in the range of ϕ = 0.83–1.2. However, Methane, Shale gas-2, and Shale gas-3 have 7.55–9.62%, 20.35–20%, 22.19–21.47 lower IMEPs than LPG in the range of ϕ = 0.83–1.2, respectively.

Gasoline compression ignition (GCI) combustion of pump-grade gasoline fuel under high compression ratio diesel engine

In this paper, gasoline compression ignition (GCI) combustion was investigated under a high compression ratio (CR = 22:1) system that was developed for a high-efficiency heavy-duty diesel engine platform. The experiment includes Single-Cylinder Engine (SCE) testing of two combustion systems with distinctively different piston designs: wave and stepped-lip. Validated Computational Fluid Dynamics (CFD) simulations provide insights on the in-cylinder phenomenon under GCI combustion. While early spray/flame and ignition characteristics were driven mainly by nozzle configuration in each combustion system, flame-wall and flame-flame interaction during the late-cycle combustion process were strongly affected by the piston's wall-flow-guided feature. The wave piston is unique with a recirculation flow, also known as radial mixing zone (RMZ). RMZ results from in-cylinder flow interactions of adjacent flames, which play a crucial part in enhancing late-cycle soot oxidation.Meanwhile, the stepped-lip piston splits flame jet (at the time of impingement) upward and downward to head and bowl, respectively. Overall, the stepped-lip piston showed lower heat loss due to reduced spray penetration. In contrast, wave piston demonstrated superior end-cycle mixing, reducing soot emissions. Both systems provided similar indicated thermal efficiency (ITE). Comparison between diesel and GCI shows that GCI can reach diesel-like efficiency while maintaining low soot emissions. However, there is a remaining challenge in GCI combustion with higher carbon monoxide (CO) and unburned hydrocarbon (UHC) emissions than diesel combustion.

A numerical study of the effects of oxy-fuel combustion under homogeneous charge compression ignition regime

The European Union (EU) has recently adopted new directives to reduce the level of pollutant emissions from non-road mobile machinery engines. The main scope of project RIVER for which this study is relating is to develop possible solutions to achieve nitrogen-free combustion and zero-carbon emissions in diesel engines. RIVER aims to apply oxy-fuel combustion with Carbon Capture and Storage (CCS) technology to eliminate NOx emissions and to capture and store carbon emissions. As part of this project, a computational fluid dynamic (CFD) analysis has been performed to investigate the effects of oxy-fuel combustion on combustion characteristics and engine operating conditions in a diesel engine under Homogenous Charge Compression Ignition (HCCI) mode. A reduced chemical n-heptane-n-butanol-PAH mechanism which consists of 76 species and 349 reactions has been applied for oxy-fuel HCCI combustion modeling. Different diluent strategies based on the volume fraction of oxygen and a diluent gas has been considered over a wide range of air-fuel equivalence ratios. Variation in the diluent ratio has been achieved by adding different percentages of carbon dioxide for a range from 77 to 83 vol.% in the intake charge. Results show that indicated thermal efficiency (ITE) has reduced from 32.7% to 20.9% as the CO2 concentration has increased from 77% to 83% at low engine loads while it doesn’t bring any remarkable change at high engine loads. It has also found that this technology has brought CO and PM emissions to a very ultra-low level (near zero) while NOx emissions have been completely eliminated.

The performance and emissions characteristics of diesel/biodiesel/alcohol blends in a diesel engine

Biodiesel has great potential as an alternative fuel for diesel engines. However, poor low-temperature flow property and high viscosity of biodiesel limit its use in engines. Therefore, alcohol comes into researchers’ eyes as a promising additive for diesel–biodiesel (DB) blends. In this study, the effects of lower and higher alcohol contents with different speeds on combustion and emissions characteristics were investigated in a modified single cylinder diesel engine. The results indicated that the maximum pressure rise rate (MPRR) maintained a consistent drop ratio as speed increased from 1500 rpm to 1800 rpm for the tested fuels. However, B10E10 (10% biodiesel and %10 ethanol by volume) had a big drop, which meant that engine’s power ability had a big loss at high speed. The declining rate with speed decreased for indicated thermal efficiency (ITE) when adding alcohol to diesel–biodiesel blends, especially n-pentanol. Moreover, compared with other tested fuels, B10P10 (10% biodiesel and 10% n-pentanol) had smaller cycle variation and more stable combustion state as speed changed, despite it had the highest coefficient of variation (COV) at 1000 rpm. It can be found that has advantages in combustion stability, and can well reduce the total hydrocarbon (THC) and carbon monoxide (CO) emissions under the condition of medium speed commonly used by vehicle. Overall consideration, using diesel/biodiesel/alcohol ternary fuels may be a better choice for diesel engines.