Low Temperature Combustion Research Articles

Gray Correlation Analysis of CO Generation Pattern during Process of Low-temperature Spontaneous combustion of Jurassic Coal

ABSTRACT Spontaneous combustion of coal is a phenomenon that exists in all coal mining countries. The characteristics of CO production during the spontaneous combustion of coal are the focus of attention of researchers. A novel programmed oxidation heating simulation system with a small-sample size was developed to study the combustion characteristics. The device was used to study the characteristics of CO generation during low-temperature coal oxidation under different conditions (three coal ranks, six particle sizes, four air volumes, and four oxygen concentrations). The microscopic characteristics of the coal structure were tested through Fourier-transform infrared spectroscopy (FTIR), and three types of active functional groups were observed. Ten factors affecting gas production in the low-temperature oxidation stage were analyzed by gray correlation. This study found that moisture in coal had the greatest effect on CO generation, followed by O-containing functional groups. Aliphatic hydrocarbons had the least correlation with CO generation. Further, the CO concentration increased exponentially during the heating process in low-temperature oxidation. In the low-temperature stage, carboxyl, carbonyl, and side-chain C–O bonds of the benzene ring were the main sources of CO generation.

Enhanced low-temperature stable combustion of hydrocarbon with suppressing the Leidenfrost effect

Low-temperature stable combustion of liquid hydrocarbons helps improve energy efficiency and alleviate environmental pollution. However, when hydrocarbons (mainly saturated ones) are used as aircraft fuel, they show a long ignition delay time (IDT) and high ignition temperature as a result of Leidenfrost effect and chemical inertness of the CH bond. In especial, the insulated fuel vapor film due to the Leidenfrost effect that inhibits the heat transfer efficiency in the wide Leidenfrost region is unfavorable. Herein, we first propose a strategy that combines low-temperature self-oxidation and enhanced heat conduction to achieve low-temperature stable combustion of hydrocarbon while suppressing the Leidenfrost effect. Specifically, moderately reactive organometallic compound methoxydiethylborane (MDEB) with special radicals and silver nanoparticles (Ag NPs) with high thermal conductivity are preferred as fuel modifiers. By thermodynamic calculation, the heat released by the self-oxidation of MDEB is two orders of magnitude higher than the evaporation latent heat of n-decane, suggesting the applicability of energy conversion supported by enhancing fuel reactivity in suppressing the Leidenfrost effect. Ignition experiment results show that the negative temperature dependence associated with the Leidenfrost effect is eliminated under the specific fuel composition. Encouragingly, compared with n-decane, the IDT of MDEB/Ag/n-decane hybrid fuel is reduced from 4027 to ∼10 ms at a surface temperature of 600 °C. Comparing the ignition of MDEB/Ag/n-decane and MDEB/n-decane hybrid fuels at same temperatures, the influence of Ag NPs on IDT is highlighted by its significant decrease (∼28%). The minimum ignition temperature of n-decane-based hybrid fuel decreases to 112 °C, which is 508 °C lower than that of n-decane. These two ignition characteristic values are the low limit of saturated hydrocarbons to date. Our results thus provide a promising tool for enhancing the low-temperature ignition reliability and combustion stability of liquid hydrocarbons, which potentially decreases the pollution from the low temperature combustion.

Optimization of the exergy efficiency, exergy destruction, and engine noise index in an engine with two direct injectors using NSGA-II and artificial neural network

Direct Dual Fuel Stratification (DDFS) strategy is a novel Low Temperature Combustion (LTC) strategy that has comparable thermal efficiency to the Reactivity Controlled Compression Ignition (RCCI) strategy, while it offers more control over the combustion process and the rate of heat release. The DDFS strategy uses two direct injectors for the low- and high-reactivity fuels (gasoline and diesel) to benefit from the RCCI concept. In this study, the injection strategy of the injectors of a gasoline/diesel DDFS engine was optimized from the thermodynamic perspective to maximize exergy efficiency and minimize exergy destruction and an engine noise index. An artificial neural network was developed with 576 samples from a CFD code to predict the DDFS mode behavior, and the non-dominated sorting genetic algorithm (NSGA-II) was used to obtain the Pareto Front and the optimal solutions. Compared to the base case, the exergy efficiency of the optimal cases increased by up to 2%, exergy destruction and Peak Pressure Rise Rate (PPRR) reduced by about 2.3%, and 2 bar/deg, respectively, in the optimal solutions. NOX and soot emissions were reduced by 40% and 35%, respectively, in the best-case scenarios.

A Comprehensive Review on Low-Temperature Combustion Technologies for Emission Reduction in Diesel Engines

Diesel engines are lean burn engines; hence CO and HC emissions in the exhaust are less likely to occur in substantial amounts. The emissions of serious concern in compression ignition engines are particulate matter and nitrogen oxides because of elevated temperature conditions of combustion. Hence the researchers have strived continuously to lower down the temperature of combustion in order to bring down the emissions from CI engines. This has been tried through premixed charge compression ignition, homogeneous charge compression ignition (HCCI), gasoline compression ignition and reactivity controlled compression ignition (RCCI). In this study, an attempt has been made to critically review the literature on low-temperature combustion conditions using various conventional and alternative fuels. The problems and challenges augmented with the strategies have also been described. Water-in-diesel emulsion technology has been discussed in detail. Most of the authors agree over the positive outcomes of water-diesel emulsion for both performance and emissions simultaneously.

A numerical investigation of gasoline/diesel direct dual fuel stratification (DDFS) combustion at high loads

High-load extension is one of the biggest challenges for the low-temperature premixed combustion strategies such as partially premixed combustion (PPC) and reactivity-controlled compression ignition (RCCI). Alternatively, a different dual-fuel combustion strategy, direct dual fuel stratification (DDFS) mode, which combines the benefits of PPC and RCCI by injecting gasoline and diesel into cylinder directly, is investigated in the present study. A comprehensive numerical comparison of PPC, RCCI and DDFS was conducted, and the effects of fuel property of the near top dead center (TDC) injection as well as different injection parameters on the combustion and emission characteristics of DDFS at a typical high load were revealed. The results indicated that DDFS can effectively control the combustion rate while maintain the thermal efficiency comparable to PPC and RCCI at high loads. For DDFS combustion, the near-TDC injection is the key parameter to control the heat release rate. However, soot emissions remarkably increase owing to the diffusion-combustion nature of the near-TDC injection, and adopting lower reactivity fuel such as methanol is a good approach to further reduce the peak pressure rise rate (PPRR) and suppress soot emissions. In addition, the diesel fraction plays a dominant role in controlling combustion phasing while the gasoline fraction serves as a more important role in combustion duration, and the effects of the start of injection of gasoline and diesel on the DDFS performance become more obvious as the gasoline and diesel fractions increase. From the perspective of load extension, a lower diesel fraction should be employed to avoid excessive PPRR, however, the diesel fraction and the start of injection should be coupled properly to avoid misfire.

An experimental investigation on gasoline diesel and biofuelled RCCI combustion and its comparison with the conventional diesel combustion

Amongst all the low temperature combustion (LTC) strategies, reactivity controlled compression ignition (RCCI) is the most promising one due to their control on combustion pashing and heat release rate (HRR). This experimentation investigates the emission, performance and combustion characteristics of the modified constant speed non road single cylinder RCCI engine and its comparison with the conventional diesel engine. In RCCI operation, gasoline and blends of ethanol and gasoline, E10 and E20 were used as a low reactivity fuel (LRF), while diesel and blends of diesel and jatropha biodiesel, B10, B20 were used as a high reactivity fuel (HRF). The ratio of LRF and HRF maintained about 60:40. For RCCI operation, 10% hot exhaust gas recirculation (EGR), Injection pressure, 3 bar for PFI (port fuel injection) pressure, and 500 bar for HRF were used. Experimentation was carried out for 1500 rpm and 0, 4, 8 and 12 kg loading conditions. From experimental results, it has been concluded that, in comparison with the conventional diesel engine, for 12 kg loading condition, there was a 92% reduction in the NOx and 72% reduction in smoke opacity observed as an effect of reduction in combustion chamber temperature for E20-B20 blend. Compared to conventional diesel, there was an 11% rise in the brake thermal efficiency for the E10B10 fuel combination. As combined effects of NOx, Smoke opacity, and brake thermal efficiency are concerned, E10-B10 is the suitable combination for given operating conditions.

Towards a comprehensive understanding of mode transition between biodiesel-biobutanol dual-fuel ICCI low temperature combustion and conventional CI combustion - Part ΙΙ: A system optimization at low load

This paper investigated the mode transition between ICCI low temperature combustion and conventional CI combustion with the parameters of energy ratio, intake temperature and engine load, and the control strategies were system analyzed to improve the smoothness during the mode transition process. Results shown that the direct mode switching from ICCI combustion to CI combustion (ICCI–CI) was suitable at low engine load, but the fluctuation of IMEP was higher when direct mode transition from ICCI to CI (ICCI–CI). Retarded the biodiesel injection timing to −38 oCA ATDC in the first transitional cycle could reduce the combustion instability. Biodiesel and butanol fuel compensation in the first cycle when the combustion mode switched to ICCI also could reduce the fluctuation of IMEP, and the corresponding fuel adjustment of biodiesel and butanol were relatively small, in which the increased fuel of biodiesel and butanol were 4.5%–11.1% and 2.6%–5.3%, respectively. The fluctuation of IMEP was higher when biodiesel compensation using two transitional cycles, that was not suitable for the smoothness of CI–ICCI mode switching process. However, the butanol compensation using two transitional cycles could enhance the combustion stability and reduce the fluctuation of IMEP during the CI–ICCI mode switching.

Effect of manifold injection of n-decanol on neem biodiesel fuelled CI engine

This research aims to achieve low temperature combustion by premixing n-decanol with the air in the intake manifold in a diesel engine along with biodiesel as a primary fuel. In this experiment, neem oil methyl ester has been utilised as a primary fuel through the main injector in the volumetric ratio of 80% diesel and 20% biodiesel namely NB20 along with the manifold injection of n-decanol through a secondary injector at various concentrations such as 10%, 20%, and 30%. It is observed from the experiment that the 30% n-decanol injection produced a brake thermal efficiency of 34.5%, which was comparable to diesel fuel due to its better combustion, as evidenced by a higher heat release rate. Oxides of nitrogen and smoke were reduced simultaneously for biodiesel-n-decanol combinations due to their LTC and the maximum reduction was found for a 30% injection rate of n-decanol. It was about 11.80% for NOX, 9.57% for smoke compared to NB20. It is clearly seen that the 30% injection rate of n-decanol produced lower emissions and better performance than 10% and 20% injection rate of n-decanol. This research suggests that the NB20-n-decanol combinations in premixed combustion mode can be an attractive replacement for diesel fuel.

Potential of EGR and intake heating for load extension using gasoline-ethanol blends as low reactivity fuel in an intelligent charge compression ignition engine

Uncontrollable ignition at high load and local misfire at low load limited the reasonable operation range of low-temperature combustion. The dual-fuel intelligent charge compression ignition (ICCI) combustion utilized two direct injectors organizing the flexible stratification through various injection strategies. Exhaust gas recirculation (EGR) delays the combustion phasing to keep the ignition under control, whereas the oxidation of incomplete products and the heat release at the late stage of combustion deteriorate. Intake heating provides the heat necessary to stabilize the ignition process at low load despite complicating the intake manifold. In this work, the load extension potential of different gasoline-ethanol blends as low reactivity fuel (LRF) was investigated, while the EGR dependence at high load and intake heating influence at low load were compared in ICCI mode. The misfire problem for 50% ethanol (E50) and 85% ethanol (E85) was solved at about 40 °C intake air temperature compared with 10% ethanol (E10). When the intake air temperature was about 60 °C, the combustion efficiency for pure ethanol (E100) reached the same level, compared with others. For the high load range, E10 faced uncontrollable ignition by the single diesel injection even with an ultra-high EGR rate, leading to the adoption of a two-stage diesel injection strategy. For E100 and E85, the ignition was highly associated with the single diesel injection even in the absence of EGR. Although E50 and E85 reached over 52% thermal efficiency under different EGR rates, E50 hardly illustrated the clean combustion features like pure ethanol and E85.

Combustion and spray breakup characteristics of biodiesel for cold start application

This study investigates the split injection spray characteristics of neem (unsaturated) biodiesel and diesel at cold (283 K) and hot (333 K) weather conditions. The novelty of this work lies in achieving the improved spray atomization and smooth engine combustion characteristics of unsaturated neem biodiesel using a split injection strategy. Biodiesel in a hot condition significantly improves spray dispersion and mixing. The Single-injection case of diesel shows fast combustion, rapid heat release, and increased nitrogen oxide (NOx) emissions. Split injection introduces fuel in steps, provides more time for fuel-air mixing, and delays the start of combustion (SoC). Diesel and biodiesel with split injection show smooth heat release, low combustion temperatures, and NOx emissions. Cold condition atomization of biodiesel remains a challenge even using the split injection strategy and requires biodiesel preheating.

Experimental and Numerical Investigations into Temperature Distributions and VOC Conversion Rate of RTO

As regulations for controlling VOCs (Volatile Organic Compounds) emissions have become more and more stringent, RTO (Regenerative Thermal Oxidizer) which involves heat exchange and storage, combustion and reaction processes has to be further optimised for enhancing the VOC treatment efficiency and reducing energy consumption. In this paper, influences of operating temperature distributions and internal flow fields on gas-out VOC concentration have been studied with experimental investigation and CFD numerical simulation. Experimental results shows that combustion temperature (around the combustor) plays more critical role than thermal storage bed temperature for affecting VOC flow-out concentration. By examining the internal flow and temperature distributions, modelling results demonstrate that fast heat transfer takes place in thermal ceramic beds and high temperature areas are formed around the combustor. At about 20 seconds after a bed working for gas-in flow, the heat transfer has demonstrated obvious attenuating. The research suggests that it is very challenging for simultaneously maintaining low gas-out VOC concentration and keeping low fuel consumption and low combustion temperature in RTOs.

Potential of hydrogen/diesel reactivity controlled compression ignition (RCCI) combustion from the perspective of the second law of thermodynamics

The potential of reactivity controlled compression ignition (RCCI) combustion fueled with hydrogen and diesel (i.e. hydrogen/diesel RCCI) was evaluated using multi-dimensional simulations embedded with a reduced chemical mechanism. In hydrogen/diesel RCCI, the premixed hydrogen is ignited by the diesel, which is directly injected into the cylinder well before the top dead center. To investigate the potential benefits of hydrogen/diesel RCCI, its combustion characteristics were compared with that of gasoline/diesel RCCI from the perspective of the second law of thermodynamics. Meanwhile, the impacts of premixed energy ratio and initial pressure on the exergy distribution for hydrogen/diesel RCCI were explored. The results show that hydrogen/diesel RCCI has an advantage over gasoline/diesel RCCI in the reduction of exergy destruction due to higher combustion temperature, shorter combustion duration, and the distinctive oxidation pathways between hydrogen and gasoline. A higher proportion of exergy output work can be achieved for hydrogen/diesel RCCI under the conditions with the same total input energy and 50% heat release (CA50) point. Moreover, a larger premixed energy ratio (i.e. larger hydrogen proportion) is helpful to elevate exergy output work and reduce exergy destruction owing to higher combustion temperature and the undergoing oxidation pathways of hydrogen with less exergy destruction. A higher initial pressure yields raised exergy destruction because of lower combustion temperature and longer combustion duration, but exergy output work is increased owing to the significantly reduced exergy transfer through heat transfer.

Numerical investigation of the effect of injection strategy on a high-pressure isobaric combustion engine

High-pressure isobaric combustion adopted in the double compression expansion engine (DCEE) has the prospect to achieve higher thermal efficiency compared to conventional diesel combustion. This work numerically explored the effects of various injection strategies on the combustion and emission characteristics of isobaric combustion. The study developed a mathematical model to predict the injection rate profile. After validations, extensive simulations were conducted with a peak pressure of up to 300 bar – mimicking the high-pressure unit of DCEE. Several major engine design parameters such as the exhaust recirculation gas (EGR) rate, engine speed, injection strategy, and intake pressure were varied and evaluated. The results demonstrated that a higher EGR rate resulted in a higher exhaust loss but a lower heat transfer loss owing to the lower combustion temperature, so the thermal efficiency exhibited a firstly growing and then declining trend. Besides, a higher engine speed generated a higher thermal efficiency due to the shorter combustion duration and thus lower heat transfer loss. Consequently, a peak thermal efficiency of 47.5% was achieved at EGR = 50% and 1800 rpm. The high-pressure cylinder performance can also be improved with an appropriate introduction of the isochoric combustion, but its impact on the whole DCEE setup needs further investigation.

Scald Burns While Bathing Among Elderly People in Japan

Night baths are an essential and beloved tradition in Japanese households. The main purpose of taking a bath at the end of the day, besides hygiene, is relaxation. The aging population is rapidly growing in Japan, as one in three people are approaching the age of 65 years or older. Furthermore, with the progress of nuclear families, the number of households with only elderly people and the need for elderly care is increasing. In recent years, elderly people experienced burns caused by hot water during bathing. We report two cases of water bath burns experienced by elderly people.The first is a case of a 68-year-old woman who presented with a history of type 2 diabetes and osteoarthritis in both knees. She did not notice that the bath stopper was unplugged while she was taking a bath, and she added hot water at around 44°C. She was exposed to hot fluid on the right foot and suffered deep dermal burns. However, due to knee osteoarthritis, it became difficult for her to move. Two hours after taking a bath, she was removed from the bathtub.The second is a case of a 71-year-old woman who presented with a history of type 2 diabetes and osteoarthritis in both knees. Because the temperature of the bath was approximately 44°C, she tried to cool down the water, but it was difficult for her to move because of knee osteoarthritis. She called out for help from her family living in the neighborhood, but she could not get out. She was sitting for about 2 hours before being noticed by her family. As a result, she suffered second-degree burns on both the buttocks and soles of her feet.Prolonged exposure to thermal liquids and burns such as low-temperature burns are caused by individual factors, such as decreased perception, orthopedic disease, and difficulty in moving due to fainting, and social factors such as delay in discovery in elderly people living alone. These factors lead to an increased depth of the burn.

Investigation on low total temperature combustion characteristics of kerosene-fueled supersonic combustor

In this paper, the combustion characteristics of kerosene-fueled supersonic combustor under the conditions of Mach number 2.0, the total temperature at 700 K and the total pressure at 520 kPa (simulated flight Mach number at 3.5) were studied by using the flame stabilizing method of cavity and strut from three aspects such as blockage ratios, kerosene equivalence ratios, location and quantity of injection holes. The results showed that: (A) The combustor with the strut realized the independent and stable combustion of kerosene. The combustion-induced back pressure in the block test with blockage ratio of 20% and 10% destroyed the inlet flow conditions; while the blockage ratio was 7.3% and 5%, the incoming flow conditions when kerosene was burned stably were not destroyed. (B) The kerosene Equivalence Ratio (ER) was more likely to be disturbed upstream than the induced back pressure when it rose, and an excessively high-ER would reduce the combustion efficiency; when the equivalence ratio was constant, the combustion efficiency of the blockage ratio of 7.3% was higher than the blockage ratio of 5%. The combustion efficiencies were 0.86 (ER = 0.13) and 0.78 (ER = 0.19) when the blockage ratio was 5%, respectively; the combustion efficiencies were 0.89 (ER = 0.16) and 0.82 (ER = 0.19) when the blockage ratio was 7.3%, respectively; the combustion efficiencies were 0.51 (ER = 0.25), 0.81 (ER = 0.3), 0.65 (ER = 0.34) and 0.62 (ER = 0.42) when the blockage ratio was 20%, respectively. (C) The porous injection provided behind the strut was beneficial to the atomization of kerosene and improved the combustion efficiency of kerosene; the second injection after the cavity would reduce the combustion efficiency due to insufficient oxygen and combustion space. This study expanded the working range of ramjet and provided a reference fuel injection scheme for Turbine-Based Combined Cycle (TBCC) engine.

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

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

Characteristics of emission and light-absorption of size-segregated carbonaceous aerosol emitted from four types of coal combustion at different combustion temperatures

Coal consumed in domestic cooking and heating in rural areas of China is considered as a major source of air pollution. To efficiently represent the emission of coal burnt for residential living at various combustion regimes, four coal samples are selected for combustion experiments in the simulated air state at three different temperatures in a drop-tube furnace system in this study. Size-segregated particulate matter in flue gas from combustion of the four coal samples at different temperatures were collected by a TISCH-type Andersen eight-stage impact sampler operating synchronously with the furnace system. The emission factors of the particulate matter samples show that OC2 and OC3 are the main carbonaceous products of bituminous coal and lignite combustion. It is also found that the particulate matter from lignite flue gas contains EC1 in a large proportion and a small amount of highly-refractory EC2 and EC3 from bituminous coals. Meanwhile, in order to evaluate the light-absorption of organic carbon in particulate matter, the mass absorption cross efficiency (α/ρ) is investigated. The clear-sky radiative transfer model shows that BrC emitted from low-temperature burning leads to even positive top-of-atmosphere radiative forcing at surfaces with an albedo of 0.19. In the 300–700 nm spectral band, the simple forcing efficiency (SFE) of particulate matter sampled significantly decreases as combustion temperature and coal maturity increase. The particulate matter presents a high SFE in the range of 0.4–1.1 μm in terms of particle size.

Fuel flexibility study of various fuels with charge dilution and high compression ratio for medium-load operating RCCI engine

This study examines the dual-fuel (RCCI) combustion mode using gasoline, ethanol, methanol, and compressed natural gas (CNG) as low reactive fuels (LRF) and diesel, neem biodiesel as high reactive fuel (HRF). The fresh and diluted charge (with hot EGR) combustion is compared at a high compression ratio for medium load operation. For obtaining the near-zero NOx-soot emissions and improved performance, the feasibility of different reactivity and renewable fuels are studied. The use of methanol and gasoline as LRF and diesel as HRF with charge dilution shows improved fuel-air-mixing, reactivity stratification, and thermal efficiency. The use of ethanol and gasoline as LRF and biodiesel as HRF with charge dilution shows near-zero NOx emissions while soot emissions are above the minimum acceptable range. The use of CNG as LRF and diesel as HRF with charge dilution shows minimum thermal efficiency and high fuel consumption. The reduced combustion rate and increased premixed combustion with charge dilution result in lower combustion temperatures and pressure rise rates for G + D and M + D.

Thermochemical Recuperation to Enable Efficient Ammonia-Diesel Dual-Fuel Combustion in a Compression Ignition Engine

A thermochemical recuperation (TCR) reactor was developed and experimentally evaluated with the objective to improve dual-fuel diesel–ammonia compression ignition engines. The novel system simultaneously decomposed ammonia into a hydrogen-containing mixture to allow high diesel fuel replacement ratios and oxidized unburned ammonia emissions in the exhaust, overcoming two key shortcomings of ammonia combustion in engines from the previous literature. In the experimental work, a multi-cylinder compression ignition engine was operated in dual-fuel mode using intake-fumigated ammonia and hydrogen mixtures as the secondary fuel. A full-scale catalytic TCR reactor was constructed and generated the fuel used in the engine experiments. The results show that up to 55% of the total fuel energy was provided by ammonia on a lower heating value basis. Overall engine brake thermal efficiency increased for modes with a high exhaust temperature where ammonia decomposition conversion in the TCR reactor was high but decreased for all other modes due to poor combustion efficiency. Hydrocarbon and soot emissions were shown to increase with the replacement ratio for all modes due to lower combustion temperatures and in-cylinder oxidation processes in the late part of heat release. Engine-out oxides of nitrogen (NOx) emissions decreased with increasing diesel replacement levels for all engine modes. A higher concentration of unburned ammonia was measured in the exhaust with increasing replacement ratios. This unburned ammonia predominantly oxidized to NOx species over the oxidation catalyst used within the TCR reactor. Ammonia substitution thus increased post-TCR reactor ammonia and NOx emissions in this work. The results show, however, that engine-out NH3-to-NOx ratios were suitable for passive selective catalytic reduction, thus demonstrating that both ammonia and NOx from the engine could be readily converted to N2 if the appropriate catalyst were used in the TCR reactor.

Investigation on the autoignition characteristics of propanol and butanol isomers under diluted lean conditions for stratified low temperature combustion

Low-temperature combustion (LTC), which can be achieved through either fuel-lean mixtures or high dilution, is an effective way to reduce NOx and soot emission for an internal combustion engine. Alcohols are considered suitable fuels for LTC as they have the advantage of better fuel-air mixing, such as high autoignition resistance and fast vaporization. Propanol and butanol can be produced as bio- or electro-fuels, which are carbon-neutral and become candidates as transportation fuels. This work focuses on investigating the autoignition and emission behavior of these alcohols regarding the application in stratified LTC. The autoignition properties of propanol and butanol isomers have been investigated in a rapid compression machine (RCM) under 90% dilution, at temperatures from 800 K to 1100 K, pressures of 20 and 40 bar and equivalence ratios of 0.25, 0.5 and 0.9. Under all investigated conditions, the order of reactivity among butanol isomers is consistent, namely n-butanol > isobutanol ≅ 2-butanol > tert‑butanol, while n-propanol is always more reactive than isopropanol. The reactivity of propanol isomers is similar to that of iso and 2-butanol. It was observed in the measurement that the difference between the reactivity of different fuels was not constant in the investigated temperature range, which was explained by the autoignition chemistry transition between 800 K and 950 K. According to the modeling, emissions of all butanol and propanol isomers are similar. The non-diluted mixtures can only achieve low-temperature combustion (LTC) in extreme lean conditions, while the diluted mixtures can achieve LTC in a wider range of equivalence ratios and have both low NOx and hydrocarbon emissions.