Bar IMEP Research Articles

The effects of residual gas trapping on part load performance and emissions of a spark ignition direct injection engine fuelled with wet ethanol

Biofuels, such as ethanol, have been introduced as a solution to decrease total CO2 emissions from transport sector as well as an alternative to increase the domestic energy security against international fuel price fluctuations. The use of high water content ethanol, the so-called wet ethanol (ethanol with higher than 5% water content v/v), has been proposed to reduce ethanol production cost. This work presents the application of wet ethanol on a naturally aspirated direct injection single cylinder research engine equipped with a fully variable electro-hydraulic valve train running on stoichiometric air/fuel ratio. The negative valve overlap (NVO) strategy was used to retain high residual gas fraction (RGF) at the part load operation of 3.1 bar IMEP and 1500 rpm. Anhydrous ethanol and different wet ethanol compositions (10% and 20% water-in-ethanol content v/v) were tested for several NVO durations, as well as European RON 95 gasoline. A one-dimensional engine model was built and validated against experimental data to estimate the RGF for each operating point. It was possible to achieve stable stoichiometric operation with more than 35% RGF for anhydrous ethanol and RON 95 gasoline. On the other hand, the maximum supported RGF for stable operation decreased as the water-in-ethanol content increased. The increase in water content reduced the tolerance to hot residuals due to lower combustion temperatures, which lengthened the flame initiation and main combustion phases. Even then, the increase in NVO period resulted in net indicated efficiency gains for all fuels due to less pumping losses, lower combustion temperature, and the possibility to maintain combustion efficiency at acceptable levels even with the maximum achievable RGF of each fuel. Anhydrous ethanol presented the highest net indicated efficiencies, while 10% water-in-ethanol mixture presented slightly higher indicated efficiency compared to gasoline. 20% water-in-ethanol mixture provided the lowest indicated efficiencies over the whole range of tested RGF.

A parametric investigation of diesel/methane dual-fuel combustion progression/stages in a heavy-duty optical engine

A single-cylinder heavy-duty optical engine is used to characterize dual-fuel (DF) combustion. In experiments, methane is applied as the main fuel while directly injected pilot diesel ignites the premixed methane-air mixture close to the top-dead center (TDC). In the present study, diesel-methane DF combustion is analyzed as a function of (1) the methane equivalence ratio, (2) initial charge temperature, and (3) the quantity of pilot diesel. Experiments are conducted at 1400 rpm and a load of 9–10 bar IMEP, and DF combustion is visualized in the engine through Bowditch-designed optical access. Meanwhile, a high-speed camera records temporally resolved natural luminosity (NL) color images of the combustion event. The results of the study suggest that DF combustion based on the apparent heat release rate (HRR) data consists of three overlapping combustion stages, where the level of overlap depends on mixture fractions of both pilot-diesel and methane in the in-cylinder charge. The stages are identified by analyzing the second derivative of HRR data. The study revealed that during the first stage, most of the pilot diesel burns in the premixed mode, and that the ignition delay time (IDT) directly influences the burnt charge mixture fraction of pilot diesel and entrained premixed methane-air mixture. In addition, the first-stage combustion is visualized as initial flame kernels originating from pilot-diesel sprays. IDT is found to be especially sensitive to the methane equivalence ratio and initial charge temperature. Furthermore, the concentration of methane and the quantity of pilot diesel in the charge distinctively influence combustion duration trends.

Effect of hydrogen addition on RCCI combustion of a heavy duty diesel engine fueled with landfill gas and diesel oil

The aim of this study is to investigate the effects of hydrogen addition on RCCI combustion of an engine running on landfill gas and diesel oil. A single cylinder heavy– duty diesel engine is set in operation at 9.4 bar IMEP. A certain amount of diesel fuel per cycle is fed into the engine and hydrogen is added to landfill gas while keeping fixed fuel energy content. The developed simulation results confirm that hydrogen addition which is the most environmental friendly fuel causes the fuel consumption per any cycle to reduce. Also, the peak pressure is increased while the engine load is reduced up to 4%. Landfill gas which is enriched with hydrogen improves the rate of methane dissociation and reduces the combustion duration at the same time the engine operation would not be exposed to diesel knock. Moreover, hydrogen addition to landfill gas would reduce engine emissions considerably.

Optical analysis of flame inception and propagation in a lean-burn natural-gas spark-ignition engine with a bowl-in-piston geometry

Heavy-duty diesel engines can convert to lean-burn natural-gas spark-ignition operation through the addition of a gas injector in the intake manifold and of a spark plug in place of the diesel injector to initiate and control combustion. However, the combustion phenomena in such converted engines usually consist of two distinct stages: a fast-burning stage inside the piston bowl followed by a slow-burning stage inside the squish area. This study used flame luminosity data and in-cylinder pressure measurements to analyze flame propagation inside a bowl-in-piston geometry. The experimental results showed a low coefficient of variation and standard deviation of peak cylinder pressure, moderate rate of pressure rise, and no knocking for the lean-burn (equivalence ratio 0.66), low-speed (900 r/min), and medium-load (6.6 bar IMEP) operating condition. Flame inception had a strong effect on the flame expansion velocity, which increased fast once the flame kernel established, but it reduced near the bowl edge and the entrance of the narrow squish region. However, the burn inside the bowl was very fast. In addition, the long duration of burn inside the squish indicated a much lower flame propagation speed for the outside-the-bowl combustion, which contributed to a long decreasing tail in the apparent heat release rate. Furthermore, cycles with fast flame inception and fast burn inside the bowl had a similar end of combustion with cycles with delayed flame inception and then a retarded burn inside the bowl, which indicated that the combustion inside the squish region determined the combustion duration. Overall, the results suggested that the spark event, the flame development inside the piston bowl, and the start of the second combustion stage affected the phasing and duration of the two combustion stages, which (subsequently) can affect engine efficiency and emissions of diesel engines converted to a lean-burn natural-gas spark-ignition operation.

Interesterification optimization of waste cooking oil and ethyl acetate over homogeneous catalyst for biofuel production with engine validation

The interesterification of waste cooking oil (WCO) and ethyl acetate (ETA) are investigated in homogeneous catalyst system using sodium hydroxide (NaOH) and acetic acid (CH3COOH). Later on, the subsequent biofuel has been investigated for the combustion characteristics, gaseous and particulate matter related emissions in a single-cylinder agricultural diesel engine. In the reaction, fatty acid ethyl esters were the main product whereas triacetin by-product was formulated in a single phase biofuel. The parameters affected the free fatty acid (FFA) conversion were studied such as catalyst system, molar ratio of ETA:WCO, molar ratio of catalyst:WCO, reaction time, and temperature. The experimental results revealed that NaOH was more favorable than the acid catalyst counterpart. The 92% biofuel yield was reached from the optimization at the NaOH:WCO of 0.015:1 M ratio and the ETA:WCO of 30:1 M ratio at 80 °C in 3 h. In the engine validation at 3.4 and 6.6 bar IMEP loads, 1700 rpm speed, the results from the combustion analysis using an indicating system reveal that the WCO biofuel initiates the combustion faster with pronounce premixed combustion regime than that of diesel fuel. The specific fuel consumption of WCO biofuel was greater, leading to a slight reduction in brake thermal efficiency by 4% and 10% at 3.4 and 6.6 bar IMEP loads, respectively compared with diesel fuel. The nano-particle emissions was characterized by an electrical mobility spectrometer and analyzed in terms of particle number. The total particle number increased with smaller size when fueling with WCO biofuel. In comparison over the loads tested, the total particle number concentrations were in the ranges of 8.1 × 1011 to 1.1 × 1012 m−3 for WCO biofuel and 4.8 × 1011 to 5.7 × 1011 m−3 for diesel fuel. Meanwhile, the particle sizes were in the ranges of 182–251 nm for WCO biofuel and 279–402 nm for diesel fuel. Summarily, for the biofuel production, this homogeneous process is beneficial in terms of low-cost feedstock, glycerol-free and mild reaction condition.

Fuel Stratification and Partially Premixed Combustion With Neat n-Butanol in a Compression Ignition Engine

Homogeneous charge compression ignition (HCCI) has been considered as an ideal combustion mode for compression ignition (CI) engines due to its superb thermal efficiency and low emissions of nitrogen oxides (NOx) and particulate matter. However, a challenge that limits practical applications of HCCI is the lack of control over the combustion rate. Fuel stratification and partially premixed combustion (PPC) have considerably improved the control over the heat release profile with modulations of the ratio between premixed fuel and directly injected fuel, as well as injection timing for ignition initiation. It leverages the advantages of both conventional direct injection compression ignition and HCCI. In this study, neat n-butanol is employed to generate the fuel stratification and PPC in a single cylinder CI engine. A fuel such as n-butanol can provide additional benefits of even lower emissions and can potentially lead to a reduced carbon footprint and improved energy security if produced appropriately from biomass sources. Intake port fuel injection (PFI) of neat n-butanol is used for the delivery of the premixed fuel, while the direct injection (DI) of neat n-butanol is applied to generate the fuel stratification. Effects of PFI-DI fuel ratio, DI timing, and intake pressure on the combustion are studied in detail. Different conditions are identified at which clean and efficient combustion can be achieved at a baseline load of 6 bar IMEP. An extended load of 14 bar IMEP is demonstrated using stratified combustion with combustion phasing control.

Hydrogen-diesel dual-fuel engine optimization for CHP systems

Combined heat and power (CHP) systems utilizing an internal combustion engine benefit from improved energy efficiency, by capturing heat that is usually wasted, and reduced energy costs. The cogeneration systems can be used domestically and in remote areas for enhancing the energy security and reducing the national energy requirements.In this paper, the study focuses on the combustion optimization of the compression-ignition engine of a CHP system using the organic chemical hydride (OCH) method for the dehydrogenation of a hydrogen energy carrier. An experimental investigation was performed on a single-cylinder hydrogen-diesel dual-fuel engine for optimizing its combustion performance and reducing the harmful emissions. The engine operated at a constant speed of 1,500 rpm and 7 bar IMEP under three different hydrogen rates representing low-, medium- and high-hydrogen energy share ratios.The analysis showed that hydrogen fuel with high EGR rates and single diesel injection could provide a simultaneous reduction of carbon emissions up to 80% combined with a reduction in NOx of over 50% and an enhanced thermal efficiency. Total hydrocarbons were the only emissions deteriorated compared to the conventional diesel operation. Engine operation with 55% and 75% hydrogen energy ratios passing the Tier 4 Nonroad Compression Ignition emission standards was achieved.

Experimental investigation into the combustion characteristics of a methanol-Diesel heavy duty engine operated in RCCI mode

This study examines combustion in a dual-fuel methanol-Diesel heavy duty engine using three different methanol injection configurations: port injection into the intake manifold; direct injection during the intake stroke (DI_E) and direct injection during the compression stroke (DI_L). The latter two methanol direct injection configurations were used in the attempt to reduce HC and CO emissions, which were considerably high in the port-injected high-octane fuel RCCI combustion. Engine experiments were performed using a double Diesel injection strategy with two pilot Diesel injections (PI1 and PI2) and a constant engine speed of 1500 rpm. The effects of three parameters – the PI1 and PI2 injection timings, and the PI2/PI1 duration ratio – were investigated at 5 bar IMEP for the three methanol injection configurations. The onset of unstable combustion and excessive combustion phasing advancement imposed lower or upper limits on the sweeps over the studied parameters. The DI_L configuration achieved lower net indicated thermal efficiencies than the other two methanol injection configurations. The influences of the methanol injection pressure and methanol substitution percentage (MSP) were also investigated for the DI_L configuration at 5 bar IMEP, revealing that the combustion process was relatively insensitive to the methanol injection pressure but was adversely affected by increasing the MSP. Finally, the port and DI_L configurations were tested at various loads. Neither configuration offered any advantage over pure Diesel combustion in terms of net indicated thermal efficiency nor emissions of HC and CO, but both offered lower greenhouse gas emissions at all load points. However, only the methanol port injection configuration achieved ultra-low NOx and soot emissions at 12 bar IMEP.

The Effect of Inlet Valve Timing and Engine Speed on Dual Fuel NG-Diesel Combustion in a Large Bore Engine

High load (18 bar IMEP) dual fuel combustion of a premixed natural gas/air charge ignited by directly injected diesel fuel was studied in a large bore gas engine. A nozzle design with low flow rate was installed to inject a small diesel volume (10.4 mm3) equal an energetic amount of about two percent. The effect of compression end temperature on ignition and combustion was investigated using valve timings with early IVC (Miller) and maximum charging efficiency (MaxCC). Furthermore, the engine speed was reduced (1500 rpm to 1000 rpm) for the Miller valve timing to analyze the impact of the chemical time scale on the combustion process. During all experiments, the cylinder charge density was kept constant adjusting the intake pressure and the resulting air mass flow. Unlike a typical reactivity-controlled compression ignition (RCCI) combustion process, the combustion phasing of the investigated pilot-ignited natural gas combustion was also sensitive to the injection timing besides the air-fuel equivalence ratio (AFER). As a consequence of the lower compression end temperature with Miller valve timing, the operating range of the AFER was shifted to significantly lower values (λ = 1.53 to 1.63) compared to MaxCC (λ = 1.88 to 2.08) and knocking combustion was no longer observed. Furthermore, the bijective relation between the mass fraction burnt 50% (MFB50%) as a function of the start of energizing (SoE) at a constant air-fuel equivalence ratio was no longer valid. The experiments with MaxCC valve timing revealed that this behavior is not necessarily a characteristic of the pilot ignition. In fact, conditions inhibiting the ignition and engine knock result in loss of the one-to-one pairing between SoE and MFB50%. The reduction of the engine speed extended the lean misfire limit (λ = 1.53 to 1.75) and improved the engine start behavior.

Single-cylinder engine evaluation of a multi-component diesel surrogate fuel at a part-load operating condition with conventional combustion

Simple, yet fully-representative surrogate fuels are needed to model market Diesel fuels. The surrogates must closely mimic market Diesel fuel properties and match the engine combustion and emissions behavior. To this end, the combustion and emissions performance of a market Diesel fuel and a four-component surrogate fuel were investigated using a single-cylinder, light-duty Diesel engine with contemporary combustion and fuel injection technology. The surrogate fuel, which was developed in previous work, was composed of normal-hexadecane/2,2,4,4,6,8,8-heptamethylnonane/decahydronaphthalene/1-methylnaphthalene with a volume fraction formulation of 0.37/0.33/0.18/0.12. Fuel test results showed the physical, chemical and combustion properties of the market Diesel fuel were closely matched by the surrogate. The fuels were evaluated by engine tests conducted at 1500 r/min and 9 bar IMEP. At this operating condition, the Diesel combustion process demonstrated low-temperature heat release, premixed and diffusion combustion regions. Test results from EGR and combustion phasing sweeps showed the engine combustion behavior, exhaust CO, HC, NOx, smoke and particle size distributions from the market Diesel fuel were very closely matched by the surrogate fuel. It can be concluded that under the engine conditions evaluated by this work, the four-component surrogate fuel accurately represents the market Diesel fuel. Thus, for conventional Diesel combustion conditions, the surrogate should prove useful for future applications such as kinetic mechanism development, fuel spray and combustion simulation, and further experimental investigations.

Investigation of Particle Number Emission Characteristics in a Heavy-Duty Compression Ignition Engine Fueled with Hydrotreated Vegetable Oil (HVO)

Diesel engines are one of the most important power generating units these days. Increasing greenhouse gas emissions level and the need for energy security has prompted increasing research into alternative fuels for diesel engines. Biodiesel is the most popular amongst the alternatives for diesel fuel as it is biodegradable, renewable and can be produced domestically from vegetable oils. In recent years, hydro-treated vegetable oil (HVO) has also gained popularity due to some of its advantages over biodiesel such as higher cetane number, lower deposit formation, storage stability etc. HVO is a renewable, paraffinic biobased alternative fuel for diesel engines similar to biodiesel. Unlike biodiesel, the production process for HVO involves hydrogen as catalyst instead of methanol which removes oxygen content from vegetable oil. A modified 6-cylinder heavy-duty diesel engine (modified for operation with single cylinder) was used for studying particle number emission characteristics for HVO fuel. The investigation was performed for varying fuel injection pressure at various engine operating loads (6, 8, 10, 12 and 14 bar IMEP). Five rail pressures were chosen from 800 to 2000 bar at a step of 300 bar. The results show that increase in rail pressure tends to increase nucleation mode particle number concentration (quantify the increase) while increase in engine load results in higher total particle number concentration. No significant differences were observed in soot and oxides of nitrogen (NOx) emission for HVO compared to mineral diesel. The fraction of emitted particles in the nucleation mode was observed to increase with increasing fuel injection pressure. (Less)

Impact of increasing methyl branches in aromatic hydrocarbons on diesel engine combustion and emissions

Lignocellulosic materials have been identified as potential carbon–neutral sources of sustainable power production. Catalytic conversion of lignocellulosic biomass results in liquid fuels with a variety of aromatic molecules. This paper investigates the combustion characteristics and exhaust emissions of a series of alkylbenzenes, of varying number of methyl branches on the monocyclic aromatic ring, when combusted in a direct injection, single cylinder, compression-ignition engine. In addition, benzaldehyde (an aldehyde (-CHO) branch on the monocyclic ring) was also tested. All the molecules were blended with heptane in different proportions, up to 60% wt/wt. The tests were conducted at a constant engine speed of 1200 rpm, a fixed engine load 4 bar IMEP, and at two injection modes: constant start of fuel injection at 10 CAD BTDC, and varying fuel injection timing to maintain constant start of fuel combustion at TDC.The results showed that the ignition delay period increased with increasing number of methyl branches on the ring, due to the rapid consumption of OH radicals by the alkylbenzenes for oxidation to stable benzyl radicals. Peak heat release rates, and concurrently NOx emissions, initially increased with increasing methyl branches, but subsequently both decreased as the bulk of heat release occurred further into the expansion stroke with significant thermal energy losses. With the exception of toluene, the number of particles in the engine exhaust increased as the number of methyl branches on the aromatic ring increased, attributable to the formation of thermally stable benzyl radicals.

Investigation of ignition characteristics and performance of a neat n-butanol direct injection compression ignition engine at low load

Neat (100%) n-butanol was implemented in a direct injection (DI) compression ignition (CI) engine. The ignition, combustion, and emission characteristics at low engine load (below 6.5bar IMEP), including near idling, were investigated. The engine experiments were performed using a modern common rail type single cylinder DI CI engine with a compression ratio of 18.2:1. Chemical kinetic simulations were also conducted to analyze the ignition characteristics of the experiments. The research results showed that neat n-butanol could not be auto-ignited at normal intake temperature and pressure conditions due to its low reactivity. However, the use of a high intake pressure of 0.75bar gauge, and an injection timing of −26° ATDC at 5.0bar IMEP, enabled auto-ignition even without the use of intake heating. One possible reason for this was attributed to the enhancement of the low temperature reaction regime. The ignition timing advancement sensitivity to intake pressure was approximately 1.0°CA/0.1bar at 5.0bar IMEP, and a higher intake pressure allowed a wider injection timing range. A neat n-butanol fueled DI CI engine had a five times longer ignition delay and a 85% longer combustion duration than the same engine fueled with diesel at 2.0bar IMEP. However, the combustion duration tended to shorten rapidly with increasing engine load, which was the opposite tendency to diesel. At low load, the nitrogen oxides (NOx) and soot emissions were very low compared to those of diesel, whereas the total hydrocarbons (THC), formaldehyde (HCHO), and carbon monoxide (CO) were higher than those of diesel. Carbon dioxide (CO2) emission was lower than that of diesel. This could be due to the reduced CO oxidation and the lower carbon content in n-butanol. Finally, by combining the previously published results with these results in this research, fuel injection strategies and intake oxygen conditions required to achieve low NOx (≤0.60g/kWh) and soot (≤0.02g/kWh) emissions and moderated maximum cylinder pressure rise rate (≤10bar/°CA) were summarized over a wide load range of 2.0–11.5bar IMEP.

Combustion and exhaust emission characteristics, and in-cylinder gas composition, of hydrogen enriched biogas mixtures in a diesel engine

This paper presents a study undertaken on a naturally aspirated, direct injection diesel engine investigating the combustion and emission characteristics of CH4-CO2 and CH4-CO2-H2 mixtures. These aspirated gas mixtures were pilot-ignited by diesel fuel, while the engine load was varied between 0 and 7 bar IMEP by only adjusting the flow rate of the aspirated mixtures. The in-cylinder gas composition was also investigated when combusting CH4-CO2 and CH4-CO2-H2 mixtures at different engine loads, with in-cylinder samples collected using two different sampling arrangements.The results showed a longer ignition delay period and lower peak heat release rates when the proportion of CO2 was increased in the aspirated mixture. Exhaust CO2 emissions were observed to be higher for 60CH4:40CO2 mixture, but lower for the 80CH4:20CO2 mixture as compared to diesel fuel only combustion at all engine loads. Both exhaust and in-cylinder NOx levels were observed to decrease when the proportion of CO2 was increased; NOx levels increased when the proportion of H2 was increased in the aspirated mixture. In-cylinder NOx levels were observed to be higher in the region between the sprays as compared to within the spray core, attributable to higher gas temperatures reached, post ignition, in that region.

Influence of combusting methane-hydrogen mixtures on compression–ignition engine exhaust emissions and in-cylinder gas composition

The paper presents an experimental investigation of combusting methane-hydrogen mixtures, pilot-ignited by diesel fuel, on a naturally aspirated, direct injection compression ignition engine. The tests were performed with two diesel fuel flow rates for pilot-ignition, and the engine was supplied with different quantities of methane-hydrogen mixtures (in various proportions) to vary the engine load between 0 and 7 bar IMEP. In addition, engine in-cylinder gas samples were collected with two geometric sampling arrangements and at various instants during the engine cycle, to measure species concentrations within the engine cylinder.The results showed lower exhaust CO2 and particulate emissions at all engine loads when combusting methane-hydrogen mixtures as compared to diesel fuel only. CO and unburned THC emissions were higher for methane-hydrogen mixtures at all engine loads when compared with diesel fuel only. NOx emissions increased with increasing proportion of hydrogen in the aspirated mixture at all engine loads. In-cylinder NOx levels were observed to be higher in the region between the fuel sprays as compared to within the spray core, attributable to higher temperatures reached in between the sprays post ignition.

An investigation of the effect of post-injection schemes on soot reduction potential using optical diagnostics in a single-cylinder optical diesel engine

This work employs a combination of pressure trace analysis, high-speed optical measurements and laser-based techniques for the assessment of the effects of various post-injection schemes on the soot reduction potential in an optical single-cylinder light-duty diesel engine. The engine was operated under a multiple injection scheme of two pilot and one main injection, typical of a partially premixed combustion mode, at the lower end of the load and engine speed range (ca 2.0 bar IMEP at 1200 r/min). Experiments considering the influence of the post-injection fuel amount (up to 15% of the total fuel quantity per cycle) and the post-injection timing within the expansion stroke (5, 10 and 15 CAD aTDC), under a constant total fuel mass per cycle, have been conducted. Findings were analysed via means of pressure trace and apparent rate of heat transfer analyses, as well as a series of optical diagnostic techniques, namely, high-speed flame natural luminosity imaging, CH*, [Formula: see text] and OH* line-of-sight chemiluminescence, as well as planar laser-induced incandescence measurements at 31 and 50 CAD aTDC. The combination of post-injection fuel amount and timing has substantial effects on charge reactivity and soot oxidation potential. The analysis reveals that an amount of fuel (7% of the total fuel mass per cycle) injected more than 10 CAD after the main combustion event leads to higher levels of soot emissions, while a larger amount of fuel (15% of the total fuel mass) injected 5 CAD after the main combustion event appears to have a beneficial effect on the soot oxidation processes. Overall, results indicate that a post-injection scheme close to the main combustion phasing could reduce soot levels and improve engine performance, that is, higher IMEP levels at the same fuel consumption rates, although it could increase engine noise.

Numerical comparison of PCCI combustion and emission of diesel and biodiesel fuels at low load conditions using 3D-CFD models coupled with chemical kinetics

LTC (Low Temperature Combustion) has demonstrated abilities to lower diesel engine emissions while achievement of better fuel economy in comparison with conventional combustion. One of the major LTC methods is PCCI (Premixed Charge Compression Ignition) combustion strategy in which high levels of EGR (exhaust gas recirculation) is utilized to reduce overall combustion temperatures and to lengthen the ignition delay. Increase in ignition delay provides time for fuel evaporation and reduces in-homogeneities in the reactant mixture, thus NOx formation from local temperature spikes and Soot formation from locally rich mixtures can be reduced. However, as dilution is increased to the limits, Soot, HC and CO can significantly increase. One of the ways to control these emissions in PCCI combustion is utilizing biodiesel fuel due to its different physical and chemical properties compared to petroleum-based diesel fuel. Hence, in the present work, a numerical study is performed to compare the combustion, performance and emission characteristics of neat biodiesel and diesel fuel surrogates under the condition of PCCI combustion mode in a light-duty, single-cylinder diesel engine by KIVA-CHEMKIN code. The operating conditions are at the engine speed of 2000rpm and load of 5.5bar IMEP. Simulations are capable of capturing, not only the bulk combustion characteristics, as well as the first and second-stage combustion processes, but also the details of the important reactive species and emission formation. For both diesel and biodiesel fuels, it has been tried to find optimum cases which are only based on sweep of injection timing and do the comparisons at those optimum states. The results indicate that for both diesel and biodiesel fuels, −30 CAD ATDC SOI timing can be regarded as an optimum SOI timing for the lowest NOx+THC and CO emissions. For the optimum case, NOx, CO, THC, thermal efficiency and ISFC for the biodiesel case are lowered by 13%, 27%, 12%, 9.5% and increased by 6%, respectively compared to the diesel case.

Diesel-Like Efficiency Using Compressed Natural Gas/Diesel Dual-Fuel Combustion

The use of natural gas in compression ignition (CI) engines as a supplement to diesel under dual-fuel combustion mode is a promising technique to increase efficiency and reduce emissions. In this study, the effect of dual-fuel operating mode on combustion characteristics, engine performance and pollutant emissions of a diesel engine using natural gas as primary fuel and neat diesel as pilot fuel, has been examined. Natural gas (99% methane) was port injected into an AVL 5402 single cylinder diesel research engine under various engine operating conditions and up to 90% substitution was achieved. In addition, neat diesel was also tested as a baseline for comparison. The experiments were conducted at three different speeds—1200, 1500, and 2000 rpm, and at different diesel-equivalent loads (injection quantity)—15, 20 (7 bar IMEP), and 25 mg/cycle. Both performance and emissions data are presented and discussed. The performance was evaluated through measurements of in-cylinder pressure, power output and various exhaust emissions including unburned hydrocarbons (UHCs), carbon monoxide (CO), nitrogen oxides (NOx), and soot. The goal of these experiments was to maximize the efficiency. This was done as follows—the compressed natural gas (CNG) substitution rate (based on energy) was increased from 30% to 90% at fixed engine conditions, to identify the optimum CNG substitution rate. Then using that rate, a main injection timing sweep was performed. Under these optimized conditions, combustion behavior was also compared between single, double, and triple injections. Finally, a load and speed sweep at the optimum CNG rate and timings were performed. It was found that a 70% CNG substitution provided the highest indicated thermal efficiency (ITE). It appears that dual-fuel combustion has a maximum brake torque (MBT) diesel injection timing for different conditions which provides the highest torque. Based on multiple diesel injection tests, it was found that the conditions that favor pure diesel combustion, also favor dual-fuel combustion because better diesel combustion provides better ignition and combustion for the CNG-air mixture. For 70% CNG dual-fuel combustion, multiple diesel injections showed an increase in the efficiency. Based on the experiments conducted, diesel-CNG dual-fuel combustion is able to achieve similar efficiency and reduced emissions relative to pure diesel combustion. As such, CNG can be effectively used to substitute for diesel fuel in CI engines.

Understanding the performance of the multiple injection gasoline partially premixed combustion concept implemented in a 2-Stroke high speed direct injection compression ignition engine

The newly designed Partially Premixed Combustion (PPC) concept operating with high octane fuels like gasoline has confirmed the possibility to combine low NOx and soot emissions keeping high indicated efficiencies, while offering a control over combustion profile and phasing through the injection settings. The potential of this PPC concept regarding pollutant control was experimentally evaluated using a commercial gasoline with Research Octane Number (RON) of 95 in a newly-designed 2-Stroke poppet valves Compression Ignition (CI) engine for automotive applications. Previous experimental results confirmed how the wide control of the cylinder gas temperature provided by the air management settings brings the possibility to achieve stable gasoline PPC combustion at low and medium speed conditions (1250–2000rpm) for the whole load range (3.1–10.4bar IMEP) with good combustion stability (Coefficient of Variation (CoV) of IMEP below 3%), high combustion efficiency (over 97%), and low NOx/soot levels.In this context, present research focuses on the two main specific drawbacks of this concept. Firstly, the high Brake Specific Fuel Consumption (BSFC) due to the work required by the mechanical supercharger since the turbocharging system does not provide the suitable pressure ratio at low speeds. Secondly, the high level of noise generated by the combustion process, especially at high loads. Therefore, a dedicated analysis has been carried out to fully exploit the benefits of the gasoline PPC concept combined with the innovative 2-Stroke engine architecture with the aim of identify and break the most relevant trade-offs.

Ethanol-fueled low temperature combustion: A pathway to clean and efficient diesel engine cycles

Low temperature combustion (LTC) in diesel engines offers the benefits of ultra-low NOx and smoke emissions but suffers from lowered energy efficiency due to the high reactivity and low volatility of diesel fuel. Ethanol from renewable biomass provides a viable alternate to the petroleum based transportation fuels. The high resistance to auto-ignition (low reactivity) and its high volatility make ethanol a suitable fuel for low temperature combustion (LTC) in compression-ignition engines.In this work, a Premixed Pilot Assisted Combustion (PPAC) strategy comprising of the port fuel injection of ethanol, ignited with a single diesel pilot injection near the top dead centre has been investigated on a single-cylinder high compression ratio diesel engine. The impact of the diesel pilot injection timing, ethanol to diesel quantity ratio and exhaust gas recirculation on the emissions and efficiency are studied at 10 bar IMEP. With the lessons learnt, successful ethanol–diesel PPAC has been demonstrated up to a load of 18bar IMEP with ultra-low NOx and soot emissions across the full load range. The main challenge of PPAC is the reduced combustion efficiency especially at low loads; therefore, the authors have presented a combustion control strategy to allow high efficiency, clean combustion across the load range. This work entails to provide a detailed framework for the ethanol-fueled PPAC to be successfully implemented.