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Technical Paper

Performance and Emission Studies in a Heavy-Duty Diesel Engine Fueled with an N-Butanol and N-Heptane Blend

2019-04-02
2019-01-0575
N-butanol, as a biomass-based renewable fuel, has many superior fuel properties. It has a higher energy content and cetane number than its alcohol competitors, methanol and ethanol. Previous studies have proved that n-butanol has the capability to achieve lower emissions without sacrifice on thermal efficiency when blended with diesel. However, most studies on n-butanol are limited to low blending ratios, which restricts the improvement of emissions. In this paper, 80% by volume of n-butanol was blended with 20% by volume of n-heptane (namely BH80). The influences of various engine parameters (combustion phasing, EGR ratio, injection timing and intake pressure, respectively) on its combustion and emission characteristics are tested at different loads. The results showed that when BH80 uses more than 40% EGR, the emitted soot and nitrogen oxides (NOx) emissions are below the EURO VI legislation.
Technical Paper

Heavy-Duty Diesel Engine Spray Combustion Processes: Experiments and Numerical Simulations

2018-09-10
2018-01-1689
A contemporary approach for improving and developing the understanding of heavy-duty Diesel engine combustion processes is to use a concerted effort between experiments at well-characterized boundary conditions and detailed, high-fidelity models. In this paper, combustion processes of n-dodecane fuel sprays under heavy-duty Diesel engine conditions are investigated using this approach. Reacting fuel sprays are studied in a constant-volume pre-burn vessel at an ambient temperature of 900 K with three reference cases having specific combinations of injection pressure, ambient density and ambient oxygen concentration (80, 150 & 160 MPa - 22.8 & 40 kg/m3-15 & 20.5% O2). In addition to a free jet, two different walls were placed inside the combustion vessel to study flame-wall interaction.
Technical Paper

Investigation of Late Stage Conventional Diesel Combustion - Effect of Additives

2018-09-10
2018-01-1787
The accepted model of conventional diesel combustion [1] assumes a rich premixed flame slightly downstream of the maximum liquid penetration. The soot generated by this rich premixed flame is burnt out by a subsequent diffusion flame at the head of the jet. Even in situations in which the centre of combustion (CA50) is phased optimally to maximize efficiency, slow late stage combustion can still have a significant detrimental impact on thermal efficiency. Data is presented on potential late-stage combustion improvers in a EURO VI compliant HD engine at a range of speed and load points. The operating conditions (e.g. injection timings, EGR levels) were based on a EURO VI calibration which targets 3 g/kWh of engine-out NOx. Rates of heat release were determined from the pressure sensor data. To investigate late stage combustion, focus was made on the position in the cycle at which 90% of the fuel had combusted (CA90). An EN590 compliant fuel was tested.
Technical Paper

Effects of Different Injection Strategies and EGR on Partially Premixed Combustion

2018-09-10
2018-01-1798
Premixed Charge Compression Ignition concepts are promising to reduce NOx and soot simultaneously and keeping a high thermal efficiency. Partially premixed combustion is a single fuel variant of this new combustion concepts applying a fuel with a low cetane number to achieve the necessary long ignition delay. In this study, multiple injection strategies are studied in the partially premixed combustion approach to reach stable combustion and ultra-low NOx and soot emission at 15.5 bar gross indicated mean effective pressure. Three different injection strategies (single injection, pilot-main injection, main-post injection) are experimentally investigated on a heavy duty compression ignition engine. A fuel blend (70 vol% n-butanol and 30 vol% n-heptane) was tested. The effects of different pilot and post-injection timing, as well as Exhaust-gas Recirculation rate on different injection strategies investigated.
Technical Paper

The Impact of Operating Conditions on Post-Injection Efficacy; a Study Using Design-of-Experiments

2018-04-03
2018-01-0229
Post-injection strategies prove to be a valuable option for reducing soot emission, but experimental results often differ from publication to publication. These discrepancies are likely caused by the selected operating conditions and engine hardware in separate studies. Efforts to optimize not only engine-out soot, but simultaneously fuel economy and emissions of nitrogen oxides (NOx) complicate the understanding of post-injection effects even more. Still, the large amount of published work on the topic is gradually forming a consensus. In the current work, a Design-of-Experiments (DoE) procedure and regression analysis are used to investigate the influence of various operating conditions on post-injection scheduling and efficacy. The study targets emission reductions of soot and NOx, as well as fuel economy improvements. Experiments are conducted on a heavy-duty compression ignition engine at three load-speed combinations.
Technical Paper

Analysis of Transition from HCCI to CI via PPC with Low Octane Gasoline Fuels Using Optical Diagnostics and Soot Particle Analysis

2017-10-08
2017-01-2403
In-cylinder visualization, combustion stratification, and engine-out particulate matter (PM) emissions were investigated in an optical engine fueled with Haltermann straight-run naphtha fuel and corresponding surrogate fuel. The combustion mode was transited from homogeneous charge compression ignition (HCCI) to conventional compression ignition (CI) via partially premixed combustion (PPC). Single injection strategy with the change of start of injection (SOI) from early to late injections was employed. The high-speed color camera was used to capture the in-cylinder combustion images. The combustion stratification was analyzed based on the natural luminosity of the combustion images. The regulated emission of unburned hydrocarbon (UHC), carbon monoxide (CO) and nitrogen oxides (NOX) were measured to evaluate the combustion efficiency together with the in-cylinder rate of heat release.
Technical Paper

Influence of Nozzle Eccentricity on Spray Structures in Marine Diesel Sprays

2017-09-04
2017-24-0031
Large two-stroke marine Diesel engines have special injector geometries, which differ substantially from the configurations used in most other Diesel engine applications. One of the major differences is that injector orifices are distributed in a highly non-symmetric fashion affecting the spray characteristics. Earlier investigations demonstrated the dependency of the spray morphology on the location of the spray orifice and therefore on the resulting flow conditions at the nozzle tip. Thus, spray structure is directly influenced by the flow formation within the orifice. Following recent Large Eddy Simulation resolved spray primary breakup studies, the present paper focuses on spray secondary breakup modelling of asymmetric spray structures in Euler-Lagrangian framework based on previously obtained droplet distributions of primary breakup.
Technical Paper

Preliminary Investigation of a Bio-Based Low Sulfur Heavy Fuel Oil

2017-09-04
2017-24-0114
Recently introduced sulfur caps on marine fuels in so-called sulfur emission control areas (SECAs) are forcing shipping companies to sail on more or less automotive grade diesel in lieu of the considerably less expensive, but sulfur-laden heavy fuel oil (HFO) to which they were accustomed. This development is an opportunity for a bio-based substitute, given that most biomass is sulfur free by default. Moreover, given that biomass is typically solid to start with, cracking it to an HFO grade, which is highly viscous in nature, will involve fewer and/or less harsh process steps than would be the case if an automotive grade fuel were to be targeted. In this study, a renewable low sulfur heavy fuel oil (LSHFO) has been produced by means of subcritical water assisted lignin depolymerization in the presence of a short length surfactant, ethylene glycol monobutyl ether (EGBE).
Technical Paper

Spray Combustion Analysis of Humins

2017-09-04
2017-24-0119
Second generation biomass is an attractive renewable feedstock for transport fuels. Its sulfur content is generally negligible and the carbon cycle is reduced from millions to tens of years. One hitherto non-valorized feedstock are so-called humins, a residual product formed in the conversion of sugars to platform chemicals, such as hydroxymethylfurfural and methoxymethylfurfural, intermediates in the production of FDCA, a building block used to produce the polyethylene furanoate (PEF) bottle by Avantium. The focus of this study is to investigate the spray combustion behavior of humins as a renewable alternative for heavy fuel oil (HFO) under large two-stroke engine-like conditions in an optically accessible constant volume chamber.
Technical Paper

Redesign of a Radial Turbine Variable Stator Geometry with Optimized Free Space Parameter for Improved Efficiency

2017-09-04
2017-24-0154
The Free Space Parameter (FSP) is evaluated as a predictor for the efficiency of a Variable Geometry Turbine (VGT). Experiments show an optimum value at 2 times the vane height. However, the optimum was found to be dependent on the pressure ratio, yielding an optimum closer to 2.5 at pressures of 2 and 2.5 bar. After this validation the FSP of a conventional VGT is evaluated and an attempt is made to improve the efficiency of this turbine using the FSP. A new geometry is proposed which yields more favorable FSP values. Experiments show that at the original design point the efficiency is unchanged. However, at both larger and smaller nozzle area’s the turbine efficiency improves as predicted by the FSP values. A relative efficiency improvement of 3 to 28 % is attained.
Technical Paper

Experimental Study on the Potential of Higher Octane Number Fuels for Low Load Partially Premixed Combustion

2017-03-28
2017-01-0750
The optimal fuel for partially premixed combustion (PPC) is considered to be a gasoline boiling range fuel with an octane number around 70. Higher octane number fuels are considered problematic with low load and idle conditions. In previous studies mostly the intake air temperature did not exceed 30 °C. Possibly increasing intake air temperatures could extend the load range. In this study primary reference fuels (PRFs), blends of iso-octane and n-heptane, with octane numbers of 70, 80, and 90 are tested in an adapted commercial diesel engine under partially premixed combustion mode to investigate the potential of these higher octane number fuels in low load and idle conditions. During testing combustion phasing and intake air temperature are varied to investigate the combustion and emission characteristics under low load and idle conditions.
Technical Paper

Numerical Investigation of PPCI Combustion at Low and High Charge Stratification Levels

2017-03-28
2017-01-0739
Partially premixed compression ignition combustion is one of the low temperature combustion techniques which is being actively investigated. This approach provides a significant reduction of both soot and NOx emissions. Comparing to the homogeneous charge compression ignition mode, PPCI combustion provides better control on ignition timing and noise reduction through air-fuel mixture stratification which lowers heat release rate compared to other advanced combustion modes. In this work, CFD simulations were conducted for a low and a high air-fuel mixture stratification cases on a light-duty optical engine operating in PPCI mode. Such conditions for PRF70 as fuel were experimentally achieved by injection timing and spray targeting at similar thermodynamic conditions.
Technical Paper

Auto-Ignition of Iso-Stoichiometric Blends of Gasoline-Ethanol-Methanol (GEM) in SI, HCCI and CI Combustion Modes

2017-03-28
2017-01-0726
Gasoline-ethanol-methanol (GEM) blends, with constant stoichiometric air-to-fuel ratio (iso-stoichiometric blending rule) and equivalent to binary gasoline-ethanol blends (E2, E5, E10 and E15 in % vol.), were defined to investigate the effect of methanol and combined mixtures of ethanol and methanol when blended with three FACE (Fuels for Advanced Combustion Engines) Gasolines, I, J and A corresponding to RON 70.2, 73.8 and 83.9, respectively, and their corresponding Primary Reference Fuels (PRFs). A Cooperative Fuel Research (CFR) engine was used under Spark Ignition and Homogeneous Charge Compression Ignited modes. An ignition quality tester was utilized in the Compression Ignition mode. One of the promising properties of GEM blends, which are derived using the iso-stoichiometric blending rule, is that they maintain a constant octane number, which has led to the introduction of methanol as a drop-in fuel to supplement bio-derived ethanol.
Technical Paper

An Insight on the Spray-A Combustion Characteristics by Means of RANS and LES Simulations Using Flamelet-Based Combustion Models

2017-03-28
2017-01-0577
Advanced Computational Fluid Dynamics (CFD) modeling of reacting sprays provides access to information not available even applying the most advanced experimental techniques. This is particularly evident if the combustion model handles detailed chemical kinetic models efficiently to describe the fuel auto-ignition and oxidation processes. Complex chemistry also provides the temporal evolution of key species closely related to emissions formation, such as polycyclic aromatic hydrocarbons (PAHs) that are well-known as soot precursors. In this framework, present investigation focuses on the analysis of the so-called Spray-A combustion characteristics using two different flamelet-based combustion models. Both Reynolds-Averaged Navier-Stokes (RANS) and Large-Eddy Simulation (LES) predictions are combined to study not only the averaged spray characteristics, but also the relevance of different realizations in this particular problem.
Journal Article

Experimental and Numerical Analyses of Liquid and Spray Penetration under Heavy-Duty Diesel Engine Conditions

2016-04-05
2016-01-0861
The modeling of fuel sprays under well-characterized conditions relevant for heavy-duty Diesel engine applications, allows for detailed analyses of individual phenomena aimed at improving emission formation and fuel consumption. However, the complexity of a reacting fuel spray under heavy-duty conditions currently prohibits direct simulation. Using a systematic approach, we extrapolate available spray models to the desired conditions without inclusion of chemical reactions. For validation, experimental techniques are utilized to characterize inert sprays of n-dodecane in a high-pressure, high-temperature (900 K) constant volume vessel with full optical access. The liquid fuel spray is studied using high-speed diffused back-illumination for conditions with different densities (22.8 and 40 kg/m3) and injection pressures (150, 80 and 160 MPa), using a 0.205-mm orifice diameter nozzle.
Technical Paper

Implementation of High-Speed Laser-Induced Incandescence Imaging in CI Engines

2016-04-05
2016-01-0725
Laser-induced incandescence (LII) is a well-established technique for tracking soot, potentially enabling soot volume fraction determination. To obtain crank angle resolved data from a single cycle, a multi-kHz system should be applied. Such an approach, however, imposes certain challenges in terms of application and interpretation. The present work intends to apply such a high-speed system to an optically-accessible, compression ignition engine. Possible problems with sublimation, local gas heating or other multishot effects have been studied on an atmospheric co-flow burner prior to the engine experiments. It was found that, in this flame, fluences around 0.1 J/cm2 provide the best balance between signal-tobackground ratio, and soot sublimation. This fluence is well below the plateau regime of LII, which poses additional problems with interpretation of the signal. This is especially true when a wide span of temperatures and gradients is present, as encountered in diesel combustion.
Technical Paper

Ignition Sensitivity Study of Partially Premixed Combustion by Using Shadowgraphy and OH* Chemiluminescence Methods

2016-04-05
2016-01-0761
Partially Premixed Combustion (PPC) is a promising combustion concept for future IC engines. However, controllability of PPC is still a challenge and needs more investigation. The scope of the present study is to investigate the ignition sensitivity of PPC to the injection timing at different injection pressures. To better understand this, high-speed shadowgraphy is used to visualize fuel injection and evaporation at different Start of Injections (SOI). Spray penetration and injection targeting are derived from shadowgraphy movies. OH* chemiluminescence is used to comprehensively study the stratification level of combustion which is helpful for interpretation of ignition sensitivity behavior. Shadowgraphy results confirm that SOI strongly affects the spray penetration and evaporation of fuel. However, spray penetration and ignition sensitivity are barely affected by the injection pressure.
Technical Paper

Combustion and Emission Characteristics of a Heavy Duty Engine Fueled with Two Ternary Blends of N-Heptane/Iso-Octane and Toluene or Benzaldehyde

2016-04-05
2016-01-0998
In this work, the influences of aromatics on combustion and emission characteristics from a heavy-duty diesel engine under various loads and exhaust gas recirculation (EGR) conditions are investigated. Tests were performed on a modified single-cylinder, constant-speed and direct-injection diesel engine. An engine exhaust particle sizer (EEPS) was used in the experiments to measure the size distribution of engine-exhaust particle emissions in the range from 5.6 to 560 nm. Two ternary blends of n-heptane, iso-octane with either toluene or benzaldehyde denoted as TRF and CRF, were tested, diesel was also tested as a reference. Test results showed that TRF has the longest ignition delay, thus providing the largest premixed fraction which is beneficial to reduce soot. However, as the load increases, higher incylinder pressure and temperature make all test fuels burn easily, leading to shorter ignition delays and more diffusion combustion.
Technical Paper

Experimental Investigation on the Characteristics of Sprays Representative for Large 2-Stroke Marine Diesel Engine Combustion Systems

2015-09-01
2015-01-1825
Fuel spray propagation and its morphology are important aspects for the in-cylinder mixture preparation in Diesel engines. Since there is still a lack of suitable measurements with regard to large 2-stroke marine Diesel engines combustion systems, a comprehensive data set of spray characteristics has been investigated using a test facility reflecting the specific features of such combustion systems. The spray penetration, area and cone angle were analysed for a variation of gas density (including the behaviour at evaporation and non-evaporating conditions), injection pressure and nozzle diameter. Moreover, spray and swirl flow interaction as well as fuel quality influences have been studied. To analyse the impacts and effects of each measured parameter, an empirical correlation for the spray penetration has been derived and discussed for all measurements presented.
Technical Paper

Validation of a Reduced Chemical Mechanism Coupled to CFD Model in a 2-Stroke HCCI Engine

2015-04-14
2015-01-0392
Homogeneous Charge Compression Ignition (HCCI) combustion technology has demonstrated a profound potential to decrease both emissions and fuel consumption. In this way, the significance of the 2-stroke HCCI engine has been underestimated as it can provide more power stroke in comparison to a 4-stroke engine. Moreover, the mass of trapped residual gases is much larger in a 2-stroke engine, causing higher initial charge temperatures, which leads to easier auto-ignition. For controlling 2-stroke HCCI engines, it is vital to find optimized simulation approaches of HCCI combustion with a focus on ignition timing. In this study, a Computational Fluid Dynamic (CFD) model for a 2-stroke gasoline engine was developed coupled to a semi-detailed chemical mechanism of iso-octane to investigate the simulation capability of the considered chemical mechanism and the effects of different simulation parameters such as the turbulence model, grid density and time step size.
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