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Toluene primary reference fuel (TPRF) mixtures containing iso-octane (i-C8H18), n-heptane (n-C7H16), and toluene (C6H5CH3) are commonly used as gasoline surrogates. We report the occurrence of super adiabatic flame temperature (SAFT) during the premixed combustion of TPRF mixtures in air. Both 1-D premixed flame and 0-D (well-stirred) reactor configurations have been considered for chemical kinetic analysis with Cantera version 2.5.1. A recently developed detailed gasoline surrogate mechanism (C3MechV3.3) has been used for the 0-D reactor analysis. On the other hand, the flame structures have been simulated with a skeletal mechanism. To ensure accurate analysis, the mechanisms used in this work have been validated at SAFT relevant conditions against experimental data from literature. For the first time in literature, post-flame heat release and brute force reaction sensitivity analysis have been performed to identify important reactions contributing towards SAFT in TPRF surrogates. The degree of superadiabaticity for 1-D and 0-D cases have been expressed with non-dimensional parameters ξ1D and ξ0D respectively. The results show that ξ1D and ξ0D increase with the increase in iso-octane content in TPRF compositions, while n-heptane and toluene have minor influence on SAFT. Key chemical observations to the SAFT mechanism in gasoline surrogate mixtures include: 1) The competition between the exothermic reaction zone and the endothermic post-flame region causes SAFT. 2) Both 1-D flame and 0-D reactor analysis show that the reactions involving H, OH, and C3 species have major influence on SAFT. 3) Iso-octane augments SAFT as its β-scission product iso-butene (i-C4H8) influences the post-flame endothermicity and C3 species formation.

Funding Information: This work was funded by Neste Corporation. Publisher Copyright: © 2021 The Authors. Published by American Chemical Society. Research Octane Number (RON), among other autoignition related properties, is a primary indicator of the grade of spark-ignition (SI) fuels. However, in many cases, the blending of various gasoline components affects the RON of the final fuel product in a nonlinear way. Currently, the lack of precise predictive models for RON challenges the accurate blending and production of commercial SI fuels. This study compares popular Machine Learning (ML) algorithms and evaluates their potential to develop state-of-the-art models able to predict key SI fuel properties. Typical gasoline composition was simplified and represented by a palette of seven characteristic molecules, including five hydrocarbons and two oxygenated species. Ordinary Least Squares (OLS), Nearest Neighbors (NN), Support Vector Machines (SVM), Decision Trees (DT), and Random Forest (RF) algorithms were trained, cross-validated, and tested using a database containing 243 gasoline-like fuel blends with known RON. Best results were obtained with nonlinear SVM algorithms able to reproduce synergistic and antagonistic molecular interactions. The Mean Absolute Error (MAE) on the test set was equal to 0.9, and the estimator maintained its accuracy when alterations were performed on the training data set. Linear methods performed better using molar compositions while predictions on a volumetric basis required nonlinear algorithms for satisfactory accuracy. Developed models allow one to quantify the nonlinear blending behavior of different hydrocarbons and oxygenates accounting for those effects during fuel blending and production. Moreover, these models contribute to a deeper understanding of the phenomena that will facilitate the introduction of alternative gasoline recipes and components.

Regulated and unregulated emissions from two Euro 6b diesel passenger cars tested using three different blends of hydrotreated vegetable oil (HVO), fossil diesel and commercial diesel (B7) were investigated at 23 °C and −7 °C using the World harmonized Light-duty vehicle Test Procedure at the Vehicle Emission Laboratory of the European Commission Joint Research Centre Ispra, Italy. The HVO blends used were: Neat HVO (100 vol% HVO), 30 vol% HVO and 7 vol% HVO. One of the vehicles was also tested using the three HVO blends on-road following a RDE compliant route. Overall, the use of different HVO blends and diesel did not lead to fuel related trends on the emissions of the tested vehicles in the laboratory nor on-road. However, HVO-100 resulted in ∼4% lower CO2 emissions than the other fuel tested in all the studied conditions. Low ambient temperature caused an increase of the emissions of studied compounds (with the exception of NH3) with all tested blends. The experimental results showed that in many cases the observed outcomes were probably attributable to a combination of combustion effects, after-treatment effects, and their control strategy.

Funding Information: This work was funded by Neste Oy. The authors acknowledge the computational resources provided by the Aalto Science-IT project. Publisher Copyright: © 2021 The Author(s)

The new emission legislation for sea-going vessels issued by the International Maritime Organization (IMO) requires drastic reduction in exhaust gas nitrogen oxides (NOx), and the combination of different primary methods can be an interesting solution without increasing remarkably the machinery. In this paper, the Miller cycle and the dilution with exhaust gas in the combustion chamber were tested to reach the Tier III limits for a four-stroke marine engine. In particular, the Miller cycle is used to reduce the in-cylinder temperature, and lower oxygen content in the combustion chamber is realized with cooled exhaust gas recirculation (EGR). Despite a remarkable reduction in NOx, the main drawback was a significant increase in fuel consumption. Split injection is combined with the abovementioned methods, in order to improve the engine efficiency. The novelty of this study consists in the simultaneous use of a split fuel injection, the Miller cycle and EGR in a marine-size application. Along this study, combining Miller timing with a relatively low EGR rate reduces NOx emissions by 90%. On the other hand, split injection does not bring significant advantages in fuel economy, although the results with very early pilot injection suggest further studies to be realized.

In a diesel engine, diesel particulate filter is used to reduce particle matter emissions. Diesel particulate filter requires periodic regenerations under high-temperature conditions in the exhaust pipe in order to oxidize the accumulated soot. A common strategy to produce high exhaust gas temperature is to inject late post-injections after the main injection. However, this practice may dilute the engine oil, causing engine wear. Biofuel addition to petroleum diesel may increase oil dilution even more. This is related to the fuel spray characteristics, the post-injection control and the vaporization process of fuel in engine oil. In this study, spray properties of late post-injection were studied with petroleum diesel and two types of transport biofuel blends containing 30% either fatty acid methyl ester or hydro-treated vegetable oil. Three different late post-injection timings were investigated. Image sequences of the main spray flame as well as the non-combusting late post-injection spray were extracted. In order to verify oil dilution during regeneration cycle and late post-injection, oil samples from six-cylinder test engine were analyzed. According to the present experiments, differences in the spray characteristics are not significant with the tested fuels. However, higher oil dilution rates were observed with fuel blend composed of 30% fatty acid methyl ester. All the studied late post-injection timings were noted to lead to the unwanted cylinder spray/wall interaction and wall-wetting consequently diluting the engine oil. The spray/wall interaction is thoroughly explained by introducing a theoretical/computational framework which characterizes any spray/wall interaction in terms of a phase diagram for any considered operation conditions. The novelty of this study arises from (1) first comparison of fatty acid methyl ester and hydro-treated vegetable oil blends in an optical engine, (2) strong evidence on the phenomena related to post-injection phase in six-cylinder and single-cylinder optical engine configurations and (3) the development of a single-droplet model showing inevitable wall-wetting.

The upcoming emission legislation for sea-going vessels issued by the international marine organization requires drastic reduction in nitric oxides. A well-known approach for meeting these requirements is to reduce the in-cylinder temperature prior to combustion by using the so-called Miller cycle. However, the mere use of this technique presents the actual limits due to long ignition delay, which occurs when the compression temperature is very low. As a consequence, premixed combustion develops quickly, increasing the local temperature in the combustion chamber and favoring NOx formation. Splitting the fuel injection into a small pilot and a main injection can reduce the magnitude of the premixed combustion and the local in-cylinder temperatures. The work presented here is divided in two parts and is novel by being the first systematic study of split injection combined with Miller cycle in large-bore engines. In its first stage, an extensive study of the injection dwell with two intake valve closings and three timings of the main injection are analyzed. In the second stage, both injection events are shifted later in the power stroke with fixed injection dwell. Overall, the pilot injection reduced the ignition delay but dropped the peak of the premixed combustion only with the most advanced intake valve closing. This improved fuel economy, but provided no advantages as far as emissions are concerned. In addition, while increasing injection dwell reduced NOx emissions, it also increased fuel consumption. The highest achieved NOx reduction was close to 60%, with a small drawback in fuel economy.

Engine research is going toward higher specific power and downsizing. This topic is of increasing interest in compression-ignition engines, due to high output demand and more restrictive legislation. This study focuses on the influence of in-cylinder gas density and fuel injection pressure on the combustion and performance in a large-bore medium speed research engine. From a baseline setup close to a commercial engine, the specific power density was augmented by higher in-cylinder pressure ranging from 200 to 300 bar. This corresponds to gas density between 65 and 90 kg/m3 at top dead center. In addition, fuel injection pressure was varied between 1500 and 2400 bar. Based on the literature, this is the first study to report engine operation with 300 bar cylinder pressure. The results show that ignition delay is significantly reduced by increasing the injection pressure, while gas density has only a moderate effect. In addition, specific nitrogen oxides increase strongly with higher injection pressure but only moderately with higher gas density. Running with high gas density permits to improve the engine fuel economy. The test outcomes also show that the combustion duration can be decreased by increasing the in-cylinder density.

In this experimental study, the ethanol/gasoline blend E85 was used as the primary fuel in a dual-fuel combustion concept. The E85 blend was injected at low pressure into the intake manifold and the mixture was ignited via a diesel fuel injection near top dead centre. The research engine was based on a heavy-duty diesel engine equipped with a common-rail injection system. Only the duration of the diesel injection was modified in the diesel injection system during the tests – the other diesel injection parameters were not changed. The goal was to study the possibilities of using the waste material-based E85 ethanol blend on dual-fuel concept as a promising future bio-fuel option. The results were promising, though the engine was not optimised for the combustion concept being studied and minimum modifications were done to the engine. High E85 rates (up to 89%) by energy content were achieved, especially under medium load conditions. On the high and low load portions were lower, but the E85 rates were higher than 30% even in these cases. For most of the cases, the limiting issue was the pressure rise rate, but in cases with the highest portions of E85 the limiting factor was the minimum quantity of the diesel fuel enabling two phase diesel fuel injection. In all cases the E85 increased carbon-monoxide and un-burned hydrocarbon emission, but the nitrogen oxide emission decreased simultaneously in most of the cases. Smoke emissions were low in all cases, but at highest E85 rate smoke emissions further decreased to near zero value.

This work presents an alternative way of exhaust gas recirculation (EGR) systems implementation in the turbocharged compression ignition engines. This sort of EGR has been studied as well as the most commonly used EGR system, where the intake and the exhaust manifolds are directly connected with a hose. However, in authors opinion the setup described in this paper has not been investigated enough, as most of the research papers concentrate on a conventional configuration modeling and control design. A problem of overcoming a positive scavenging pressure drop and delivering high amount of EGR is addressed in this article. It comes from the fact that in this kind of engines the exhaust pressure is lower than the intake, making it difficult to deliver high and stable portion of EGR over the engine operating range. A generic mean value engine model is developed in this work and an initial simple control structure is proposed.

Limited crude oil resources and growing environmental awareness have raised a huge led to a huge motivation to seek new fuel alternatives for combustion engines. In this study the goal was to research the potential of ethanol as a compression ignition engine fuel utilizing dual-fuel combustion technology. In the studied DF (dual-fuel) concept, the primary fuel is injected into the intake manifold and it is ignited by injecting diesel fuel into the cylinder near the TDC (top-dead centre). A similar concept has been widely used in natural gas dual-fuel engines. By using ethanol as a primary fuel instead of gaseous fuel, the dual-fuel concept could be a true alternative for on-road and off-road heavy-duty vehicles without the obstacles of energy density and fuel distribution challenges of the gaseous fuels. The research engine in this study was a high speed heavy duty diesel engine modified for dual fuel combustion. The engine was equipped with a common-rail diesel injection system, which gave flexibility to modify the diesel injection to control the combustion. Especially the relationship between pilot and main diesel injection was investigated. The gathered results were promising. A maximum ethanol/diesel mass ratio of around 90% was achieved at high load conditions.

Underexpanded jets can be formed when high-pressure gaseous fuel is injected directly into an engine cylinder. In such conditions, shock waves are formed immediately near the nozzle exit. In the present study, the flow structure and turbulent mixing of pulsed jets issuing from a circular nozzle is investigated using acetone planar laser-induced fluorescence (PLIF). By monitoring axial and various radial cross-sections under different injection pressure conditions, different features of gaseous jets are visualized and interpreted. The temporal development of the axial cross-sections reveals three typical jet flow patterns (subsonic, moderately underexpanded, and highly underexpanded) during the injection. These stages are (1) well described with the observed shock structures and (2) noted to take a considerably long portion of the full injection process. The visualizations from the radial cross sections show how the nozzle inflow conditions may influence the primary and the azimuthal (secondary) instability of the jet which influences the turbulence transition process and the mixing process. The results indicate the importance of inner nozzle flow on the flow behavior. For example, systematic asymmetries in the mean concentration fields are observed. In addition to PLIF data, numerical simulations can be used to support the experimental picture of the jet behavior. We give examples of large-eddy simulations (LESs) in order to further explore the behavior of the underexpanded jets. Results show that LES is able to reproduce the basic physics of underexpanded jets. LES and PLIF compare favorably in terms of the barrel shock structures and the description of the normal shocks. LES also provides detailed flow field information including temperature, Mach number, concentration and scalar dissipation rate (SDR).

Fully paraffinic diesel fuel produced from hydrotreated vegetable oils (HVOs) is one alternative to increase the share of renewable energy in the transport sector. HVO fuel has also been shown to reduce exhaust emissions but, as the fuel contains no oxygen, even higher emissions reductions are possible by blending the HVO fuel with suitable oxygenate. From a large number of oxygenates, di-n-pentyl ether (DNPE) was chosen due to its favourable fuel properties (e.g. high cetane number and good solubility to diesel). In this paper, it was studied how fuel blend containing 2 wt.% oxygen (80 wt.% HVO and 20 wt.% DNPE) affects particulate and NOx emissions of a single-cylinder research engine. It was observed that the blend reduced emitted particulate mass 25-30% depending on load while the NOx emissions was changed under 5%. Thus, PM and NOx can possibly be both reduced e.g. by utilising EGR. In addition to emission reductions, the effects of the blend on the hygroscopic properties of produced exhaust particles were studied using a hygroscopic tandem differential mobility analyzer (HTDMA). The addition of oxygen into fuel led to a small increase in the hygroscopicity of exhaust particles.

Natural gas direct-injection (DI) with diesel pilot ignition using stratified combustion concept has been considered as a challenging and innovative technology to improve engine efficiency and meet stringent emission limits. Due to stratified mixture usually formed by late injection near the top dead center, the jet pressure ratio (PR) between injection pressure and motored in-cylinder pressure is usually very low, which may lead to poor jet mixing efficiency. In the present study, wall impingement was used to enhance the mixing process of low PR pulsed jet (PR

The effect of intake valve closure (IVC) timing by utilizing Miller cycle and start of injection (SOI) on particulate matter (PM), particle number and nitrogen oxide (NOx) emissions was studied with a hydrotreated vegetable oil (HVO)-fueled nonroad diesel engine. HVO-fueled engine emissions, including aldehyde and polyaromatic hydrocarbon (PAH) emissions, were also compared with those emitted with fossil EN590 diesel fuel. At the engine standard settings, particle number and NOx emissions decreased at all the studied load points (50%, 75%, and 100%) when the fuel was changed from EN590 to HVO. Adjusting IVC timing enabled a substantial decrease in NOx emission and combined with SOI timing adjustment somewhat smaller decrease in both NOx and particle emissions at IVC -50 and -70 degrees CA points. The HVO fuel decreased PAH emissions mainly due to the absence of aromatics. Aldehyde emissions were lower with the HVO fuel with medium (50%) load. At higher loads (75% and 100%), aldehyde emissions were slightly higher with the HVO fuel. However, the aldehyde emission levels were quite low, so no clear conclusions on the effect of fuel can be made. Overall, the study indicates that paraffinic HVO fuels are suitable for emission reduction with valve and injection timing adjustment and thus provide possibilities for engine manufacturers to meet the strictening emission limits.

Hydrotreated vegetable oil (HVO) diesel fuel is a promising biofuel candidate that can complement or substitute traditional diesel fuel in engines. It has been already reported that by changing the fuel from conventional EN590 diesel to HVO decreases exhaust emissions. However, as the fuels have certain chemical and physical differences, it is clear that the full advantage of HVO cannot be realized unless the engine is optimized for the new fuel. In this article, we studied how much exhaust emissions can be reduced by adjusting engine parameters for HVO. The results indicate that, with all the studied loads (50%, 75%, and 100%), particulate mass and NOx can both be reduced over 25% by engine parameter adjustments. Further, the emission reduction was even higher when the target for adjusting engine parameters was to exclusively reduce either particulates or NOx. In addition to particulate mass, different indicators of particulate emissions were also compared. These indicators included filter smoke number (FSN), total particle number, total particle surface area, and geometric mean diameter of the emitted particle size distribution. As a result of this comparison, a linear correlation between FSN and total particulate surface area at low FSN region was found.

Conventional fossil diesel fuel and renewable diesel fuel based on hydrotreated vegetable oils (HVO) were compared regarding the oxidation characteristics of the generated soot particulate. The comparison was performed by utilizing a high-temperature oxidation tandem differential mobility analyser in which monodisperse soot aerosol was first selected and then heated in a high-temperature furnace. The particle size reduction caused by oxidation during the furnace treatment was then measured as a function of furnace temperature. The results indicate that soot oxidation is very similar between the studied fuels. This is supported by the obtained HR-TEM images and EELS-spectra which were practically indistinguishable between different fuels and engine conditions. The similar oxidation properties and surface structure between fossil and HVO-based diesel fuels imply that the oxidative aftertreatment devices designed for fossil diesel should work well also with the studied renewable diesel fuel.

Hydrotreating of vegetable oils or animal fats is an alternative process to esterification for producing biobased diesel fuels. Hydrotreated products are also called renewable diesel fuels. Hydrotreated vegetable oils (HVO) do not have the detrimental effects of ester-type biodiesel fuels, like increased NO x emission, deposit formation, storage stability problems, more rapid aging of engine oil or poor cold properties. HVOs are straight chain paraffinic hydrocarbons that are free of aromatics, oxygen and sulfur and have high cetane numbers. In this paper, NO x ‐ particulate emission trade-off and NO x ‐ fuel consumption trade-off are studied using different fuel injection timings in a turbocharged charge air cooled common rail heavy duty diesel engine. Tested fuels were sulfur free diesel fuel, neat HVO, and a 30% HVO + 70% diesel fuel blend. The study shows that there is potential for optimizing engine settings together with enhanced fuel composition. HVO could be used in optimized low emission diesel power trains in captive fleet applications like city buses, indoor fork-lift trucks, or mine vehicles.

The scope of this experimental engine study was to explore the effect of charge air temperature on E85 ethanol/gasoline blend dual-fuel combustion. The E85 was injected in the intake manifold, while diesel fuel was direct injected into the cylinder with a common-rail injection system. The study focused on medium and high load conditions at 1500 rpm. The diesel injection timing parameters were kept in every test case the same as in the original diesel production engine. The results showed that charge air temperature influenced the ignition delay, the cylinder pressure rise rate (PRR) and the maximum cylinder pressure by altering the E85 combustion phasing, while the changes on the diesel fuel combustion were minor. Lower charge air temperatures allowed higher E85 injection rates without the risk of a too high PRR, especially at high load conditions. The increase of the E85 rate allowed by lower charge air temperature, decreased nitrogen oxide emission, but simultaneously increased carbon monoxide and unburned total hydrocarbon emissions and decreased combustion efficiency.

Over the past decade significant research and development activities have been invested in alternative fuels in order to reduce our dependency on fossil fuel sources and reduce CO2 and local emissions from traffic. One result of these R&D efforts is paraffinic diesel fuels, which can be used with existing vehicle fleets and infrastructures. Paraffinic diesels also have other benefits compared to conventional diesels, for example a very high cetane number and the lack of sulfur and aromatic compounds. These characteristics are beneficial in terms of exhaust gas emissions, something which has been demonstrated in numerous studies. The objective of this study was to develop low-emission combustion technologies for paraffinic renewable diesel in a compression ignition engine, and to study the possible benefits of oxygenated paraffinic diesel. Hydrotreated vegetable oil (HVO), which is a commercial example of paraffinic, renewable diesel, was used with and without oxygenate in comparison with conventional diesel. Exhaust emissions were measured in three steady state conditions. The adjusted engine parameters, such as inlet valve closure and injection timing, injection pressure and amount of exhaust gas recirculation (EGR) were optimized for HVO. The results demonstrate that significant reductions of particulate matter (48-61%), polyaromatic hydrocarbon (75-87%) and NOx (31-54%) emissions can be achieved simultaneously by using HVO with adjusted engine parameters.

This paper describes an investigation of the jet structure and mixture formation process of wall-impinging gas jet injected by a low pressure gas injector in a constant volume chamber at room conditions. The tracer-based planar laser-induced fluorescence (PLIF) technique is applied to qualitatively evaluate the mixture formation process. The macroscopic structure and concentration distribution of wall-impinging jet were studied based on a series of time evolution high-definition images. In particular, the effects of injection pressure on characteristics of turbulence were investigated. Experimental results show that vortex structure with large scale is one of important characteristics for wall-impinging jet, and the interaction among jet flow, impingement wall, and surrounding air plays a dominant role in the mixture formation. The comparative study about the effect of injection pressure on wall-impinging jet reveals higher injection leads to higher mixing efficiency and better mixture formation.