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Simulation Based Investigation of Achieving Low Temperature Combustion with Methanol in a Direct Injected Compression Ignition Engine

Lund University-Erik Svensson, Sebastian Verhelst
Published 2019-04-02 by SAE International in United States
Low temperature combustion concepts used in compression ignition engines have shown to be able to produce simultaneous reduction of oxides of nitrogen and soot as well as generating higher gross indicated efficiencies compared to conventional diesel combustion. This is achieved by a combination of premixing, dilution and optimization of combustion phasing. Low temperature combustion can be complemented by moving away from fossil fuels in order to reduce the net output of CO2 emissions. Alternative fuels are preferably liquid and of sufficient energy density. As such methanol is proposed as a viable option. This paper reports the results from a simulation based investigation on a heavy-duty multi-cylinder direct injection compression ignition engine with standard compression ratio. The engine was simulated using two different fuels: methanol and gasoline with an octane number of 70. The primary objective of the study was to find the optimal engine settings which maximized the brake efficiency for the engine. A secondary objective was to find the optimal injection strategy and combustion mode that would result if the brake efficiency was targeted.…
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Measurement of Gasoline Exhaust Particulate Matter Emissions with a Wide-Range EGR in a Heavy-Duty Diesel Engine

Lund University-Mengqin Shen, Sam Shamun, Per Tunestal, Martin Tuner
Published 2019-04-02 by SAE International in United States
A large number of measurement techniques have been developed or adapted from other fields to measure various parameters of engine particulates. With the strict limits given by regulations on pollutant emissions, many advanced combustion strategies have been developed towards cleaner combustion. Exhaust gas recirculation (EGR) is widely applied to suppress nitrogen oxide (NOx) and reduce soot emissions. On the other hand, gasoline starts to be utilized in compression ignition engines due to great potential in soot reduction and high engine efficiency. New engine trends raise the need for good sensitivity and suitable accuracy of the PM measurement techniques to detect particulates with smaller size and low particulate mass emissions. In this work, we present a comparison between different measurement techniques for particulate matter (PM) emissions in a compression ignition engine running on gasoline fuel. A wide-range of EGR was used with lambda varied from 3 down to 1. The compared equipment includes AVL smoke meter, AVL Micro Soot Sensor, Pegasor and Cambustion Differential Mobility Spectrometer (DMS). The goal of this paper is to compare the…
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Effect of Injection Timing on the Ignition and Mode of Combustion in a HD PPC Engine Running Low Load

Lund University-Christian Ibron, Mehdi Jangi, Sara Lonn, Alexios Matamis, Oivind Andersson, Martin Tuner, Mattias Richter, Xue-Song Bai
Published 2019-04-02 by SAE International in United States
This work aims to study the effect of fuel inhomogeneity on the ignition process and subsequent combustion in a compression ignition Partially Premixed Combustion (PPC) engine using a primary reference fuel (PRF) in low load conditions. Five cases with injection timings ranging from the start of injection (SOI) at -70 crank angle degrees (CAD) to -17 CAD have been studied numerically and experimentally in a heavy duty (HD) piston bowl geometry. Intake temperature is adjusted to keep the combustion phasing constant. Three dimensional numerical simulations are performed in a closed cycle sector domain using the Reynolds Averaged Navier-Stokes (RANS) formulation with k-ϵ turbulence closure and direct coupling of finite rate chemistry. The results are compared with engine experiments. The predicted trends in required intake temperature and auto-ignition location for a constant combustion phasing are consistent with experiments. The simulations show that the auto-ignition is critically dependent on both fuel and temperature stratification. The ignition occurs in fuel-lean regions but the mixing of the fuel with the cylinder gas and the cylinder gas temperature stratification (prior…
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Interaction between Fuel Jets and Prevailing Combustion During Closely-Coupled Injections in an Optical LD Diesel Engine

Lund University-Alexios Matamis, Mattias Richter, Öivind Andersson
Volvo Car Corporation-Michael Denny, Håkan Persson
Published 2019-04-02 by SAE International in United States
Two imaging techniques are used to investigate the interaction between developed combustion from earlier injections and partially oxidized fuel (POF) of a subsequent injection. The latter is visualized by using planar laser induced fluorescence (PLIF) of formaldehyde and poly-cyclic aromatic hydrocarbons. High speed imaging captures the natural luminescence (NL) of the prevailing combustion. Three different fuel injection strategies are studied. One strategy consists of two pilot injections, with modest separations after each, followed by single main and post injections. Both of the other two strategies have three pilots followed by single main and post injections. The separations after the second and third pilots are several times shorter than in the reference case (making them closely-coupled). The closely-coupled cases have more linear heat release rates (HRR) which lead to much lower combustion noise levels. For all cases, POF is detected during the very weak HRR before the notable combustion of the first pilot injection’s fuel. When the subsequent fuel injections overlap with a local decrease in HRR, the prevailing combustion is to some degree extinguished during…
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Cylinder to Cylinder Variation Related to Gas Injection Timing on a Dual-Fuel Engine

Lund University-Menno Merts, Sebastian Verhelst
HAN University of Applied Sciences-Quintin Pet, Peter Mesman
Published 2019-04-02 by SAE International in United States
The natural gas/diesel dual-fuel engine is an interesting technique to reduce greenhouse gas emission. A limitation of this concept is the emission of un-combusted methane. In this study we analyzed the influence of PFI gas-injection timing on cylinder to cylinder gas-distribution, and the resulting methane emissions. This was done on a 6 cylinder HD engine test bench and in a GT-power simulation of the same engine. The main variable in all tests was the timing of the intake port gas injection, placed either before, after, or during the intake stroke. It showed that injecting outside of the intake window resulted in significant variation of the amount of trapped gaseous fuel over the 6 cylinders, having a strong impact on methane emissions. Injecting outside of the intake stroke results in gas awaiting in the intake port. Both testing and simulation made clear that as a result of this, cylinder 1 leans out and cylinder 6 enriches. The simulation showed how this is caused by the airflow into the manifold, which enters the manifold close to cylinder…
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The Relevance of Different Fuel Indices to Describe Autoignition Behaviour of Gasoline in Light Duty DICI Engine under PPC Mode

Lund University-Amir Aziz, Changle Li, Sebastian Verhelst, Martin Tuner
Published 2019-04-02 by SAE International in United States
Partially premixed combustion (PPC) with gasoline fuels is a new promising combustion concept for future internal combustion engines. However, many researchers have argued the capabilities of research octane number (RON) and Motor Octane Number (MON) to describe the autoignition behaviour of gasoline fuels in advanced combustion concepts like PPC. The objective of this study is to propose a new method, called PPC number, to characterize the auto ignition quality of gasoline fuels in a light-duty direct injected compression ignition engine under PPC conditions. The experimental investigations were performed on a 4-cylinder Volvo D4 2 litre engine. The ignition delay which was defined as the crank angle degrees between the start of injection (SOI) and start of combustion (SOC) was used to represent the auto ignition quality of a fuel. The ignition delays of primary reference fuels PRF (blends of n-heptane and iso-octane) were used to develop a reference curve where a PPC metric for gasoline could be based on. The PPC number of a specific gasoline is defined as the octane number of the PRF,…
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Comparison of Kinetic Mechanisms for Numerical Simulation of Methanol Combustion in DICI Heavy-Duty Engine

Lund University-Mateusz Pucilowski, Shijie Xu, Changle Li, Martin Tuner, Xue-Song Bai, Alexander A. Konnov
Northwestern Polytechnical University-Rui Li, Fei Qin
Published 2019-04-02 by SAE International in United States
The combustion process in a homogeneous charge compression ignition (HCCI) engine is mainly governed by ignition wave propagation. The in-cylinder pressure, heat release rate, and the emission characteristics are thus largely driven by the chemical kinetics of the fuel. As a result, CFD simulation of such combustion process is very sensitive to the employed reaction mechanism, which model the real chemical kinetics of the fuel. In order to perform engine simulation with a range of operating conditions and cylinder-piston geometry for the design and optimization purpose, it is essential to have a chemical kinetic mechanism that is both accurate and computational inexpensive. In this paper, we report on the evaluation of several chemical kinetic mechanisms for methanol combustion, including large mechanisms and skeletal/reduced mechanisms. These mechanisms are evaluated in terms of homogeneous ignition delay time, laminar flame speed, and multi-phase simulations of HCCI heavy-duty engine. The results are compared with experimental data and evaluated in terms of the accuracy and computational cost. It was found that scattering of ignition delay time predicted from different chemical…
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Effects of In-Cylinder Flow Simplifications on Turbulent Mixing at Varying Injection Timings in a Piston Bowl PPC Engine

Lund University-Christian Ibron, Mehdi Jangi, Xue-Song Bai
Published 2019-04-02 by SAE International in United States
In computational fluid dynamic simulations of partially premixed combustion engines it is common to find simplifications of the in cylinder flow conditions in order to save computational cost. One common simplification is to start the simulation at the moment of intake valve closing with an assumed initial flow condition, rather than making a full scavenging simulation. Another common simplification is the periodic sector assumption, limiting all sector cuts of the full cylinder to be identical periodic copies of each other. This work studies how such flow simplifications affect the spray injection and in turn the fuel/air mixing at different injection timings. Focus is put on the stratification of fuel concentration and gas temperature due to interaction of the spray, turbulence and piston geometry. The investigated engine setup consists of a light duty engine with a piston bowl and a five-hole injector. The simulations are performed under non-reacting conditions and utilize the large eddy simulation turbulence model. Both full cylinder mesh and sector mesh simulations are carried out to evaluate the effects of (a) turbulent vs…
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Study on Heat Losses during Flame Impingement in a Diesel Engine Using Phosphor Thermometry Surface Temperature Measurements

Lund University-Alexios Matamis, Mattias Richter
Scania CV AB-Christian Binder, Daniel Norling
Published 2019-04-02 by SAE International in United States
In-cylinder heat losses in diesel engines decrease engine efficiency significantly and account for approximately 14-19% [1, 2, 3] of the injected fuel energy. A great part of the heat losses during diesel combustion presumably arises from the flame impingement onto the piston. Therefore, the present study investigates the heat losses during flame impingement onto the piston bowl wall experimentally. The measurements were performed on a full metal heavy-duty diesel engine with a small optical access through a removed exhaust valve. The surface temperature at the impingement point of the flame was determined by evaluating a phosphor’s temperature dependent emission decay. Simultaneous cylinder pressure measurements and high-speed videos are associated to the surface temperature measurements in each cycle. Thus, surface temperature readings could be linked to specific impingement and combustion events. The results showed a sharp increase of the surface temperature during the flame impingement and an abrupt decrease as the flame disappeared.
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Simulation of System Brake Efficiency in a Double Compression-Expansion Engine-Concept (DCEE) Based on Experimental Combustion Data

Lund University-Nhut Lam, Per Tunestal
Volvo Global Truck Tech. Powertrain Eng.-Arne Andersson
Published 2019-01-15 by SAE International in United States
The double compression-expansion engine concepts (DCEE) are split-cycle concepts where the compression, combustion, expansion and gas exchange strokes occur in two or more different cylinders. Previous simulation studies reveal there is a potential to improve brake efficiency with these engine concepts due to improved thermodynamic and mechanical efficiencies. As a continuation of this project this paper studies an alternative layout of the DCEE-concept. The concept studied in this paper has three different cylinders, a compression, a combustion and an expansion cylinder. Overall system indicated and brake efficiency estimations were based on both engine experiments and simulations. The engine experiments were carried out at 10 different operating points and 5 fuelling rates (between 98.2 and 310.4 mg/cycle injection mass) at an engine speed of 1200 rpm. The inlet manifold pressure was varied between 3 and 5 bar. Due to concerns with structural stability the peak cylinder pressure during the engine experiments was limited to 210 bar. Exhaust backpressure was limited to 8 bar due to thermal stress on the exhaust valves. The engine experiments reveal that…
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