Fuel Dependent Heat Release Differences between Euro Diesel Fuel and RME in a HSDI Diesel Engine

In the degree that costs and demand of crude oil rise, diminish the economical disadvantages for alternative Diesel fuels, resulting in a variety of feasible substitutes. Diesel fuel substitutes have deviating exhaust emissions from conventional fuel. The methyl ester of rapeseed oil (known as RME/Biodiesel) is receiving increasing attention as an alternative fuel for Diesel engines. RME is a non-toxic, biodegradable, and renewable fuel with the potential to reduce engine exhaust emissions [1]. The main disadvantage for RME is its vaporisation and self ignition characteristics at low load conditions. Engine experiments were carried out at 4 bar IMEP with Euro Diesel fuel (EDF) as reference and RME. During these engine experiments EGR and injection pressure were varied. As a result, differences in exhaust emissions due to EGR, injection pressure and fuel type were observed. The objective of this work was to find answers for fuel dependent differences in indicated load and exhaust gas emissions. As combustion and emission formation of RME has not been fundamentally explained yet [2], a detailed analysis approach based on explanation models for fuel characteristics was chosen to explain the observed differences

Detailed Heat Release Analyses With Regard To Combustion of RME and Oxygenated Fuels in an HSDI Diesel Engine

Experiments on a modern DI Diesel engine were carried out: The engine was fuelled with standard Diesel fuel, RME and a mixture of 85% standard Diesel fuel, 5% RME and 10% higher alcohols under low load conditions (4 bar IMEP). During these experiments, different external EGR levels were applied while the injection timing was chosen in a way to keep the location of 50% heat release constant. Emission analysis results were in accordance with widely known correlations: Increasing EGR rates lowered NOx emissions. This is explained by a decrease of global air-fuel ratio entailing longer ignition delay. Local gas-fuel ratio increases during ignition delay and local combustion temperature is lowered. Exhaust gas analysis indicated further a strong increase of CO, PM and unburned HC emissions at high EGR levels. This resulted in lower combustion efficiency. PM emissions however, decreased above 50% EGR which was also in accordance with previously reported results. Besides those similar trends, fuel dependent differences in indicated thermal efficiency as well as CO, HC, NOx and especially PM emissions were observed. These differences were evaluated by detailed heat release analysis and explanation models based upon fuel characteristics as fuel viscosity and fuel distillation curve. Fuel spray evaporation and heat release were influenced by these fuel characteristics. Due to these characteristics it was concluded that RME has a higher tendency to form fuel rich zones at low load conditions than the other tested fuel types. Moreover it was found that improved fuel spray vaporisation is an option to improve exhaust emissions at low load conditions

effect of in cylinder flow structures on late cycle soot oxidation in a quiescent heavy duty diesel engine

ABSTRACTThis paper reports on CFD simulations of in-cylinder flow and combustion in an open-bowl heavy duty diesel engine at high load. The focus of the study is to unravel the effect of swirl moti..

Evolution of In-Cylinder Diesel Engine Soot and Emission Characteristics Investigated with Online Aerosol Mass Spectrometry

To design diesel engines with low environmental impact, it is important to link health and climate-relevant soot (black carbon) emission characteristics to specific combustion conditions. The in-cylinder evolution of soot properties over the combustion cycle and as a function of exhaust gas recirculation (EGR) was investigated in a modern heavy-duty diesel engine. A novel combination of a fast gas-sampling valve and a soot particle aerosol mass spectrometer (SP-AMS) enabled online measurements of the in-cylinder soot chemistry. The results show that EGR reduced the soot formation rate. However, the late cycle soot oxidation rate (soot removal) was reduced even more, and the net effect was increased soot emissions. EGR resulted in an accumulation of polycyclic aromatic hydrocarbons (PAHs) during combustion, and led to increased PAH emissions. We show that mass spectral and optical signatures of the in-cylinder soot and associated low volatility organics change dramatically from the soot formation dominated phase to the soot oxidation dominated phase. These signatures include a class of fullerene carbon clusters that we hypothesize represent less graphitized, C5-containing fullerenic (high tortuosity or curved) soot nanostructures arising from decreased combustion temperatures and increased premixing of air and fuel with EGR. Altered soot properties are of key importance when designing emission control strategies such as diesel particulate filters and when introducing novel biofuels

Quantitative in-cylinder fuel measurements in a heavy duty diesel engine using structured laser illumination planar imaging (SLIPI)

Laser-induced fluorescence (LIF) for quantitative fuel concentration measurements in a combustion engine is a challenging task. Measuring close to the walls of the combustion chamber is even more challenging as both the incident laser light and the signal are strongly reflected on the walls of the combustion chamber. By using a new technique called Structured Laser Illumination Planar Imaging (SLIPI) such background effects, as well as unwanted multiply scattered light, can be suppressed allowing for higher measurement accuracy. In this article we demonstrate, for the first time, the feasibility of the SLIPI technique for gas phase LIF and in-cylinder measurements. Results from regular LIF and SLIPI measurements are also compared. The measurements were made on a non-reacting fuel-jet with acetone as a fuel tracer in a heavy duty diesel engine (Scania D12). It is observed that the equivalence ratio measured by SLIPI in the free part of the jet is only two thirds of that measured by regular LIF during the early jet development

Influence of spatial and temporal distribution of Turbulent Kinetic Energy on heat transfer coefficient in a light duty CI engine operating with Partially Premixed Combustion

[EN] Emission regulations together with the need of more fuel-efficient engines have driven the development of promising combustion concepts in compression ignition (CI) engines. Most of these combustion concepts, lead towards a lean and low temperature combustion potentially suitable to achieve lower emission and fuel consumption levels compared to conventional diesel combustion. In this framework, Partially Premixed Combustion (PPC) using gasoline as fuel is one of the most accepted concepts. There are numerous studies focused on studying concepts such as PPC from the emissions point of view. Nonetheless, there is a lack of knowledge regarding changes in heat transfer introduced by the use of these combustion concepts. It is worth noting that heat transfer can be considered as a key aspect behind possible engine performance improvements. Thus, the reliable estimation of this parameter is of considerable importance. Additionally, a better understanding of how events such as injection and combustion might affect heat transfer is also relevant. To gain insight into gasoline PPC heat transfer coefficient, its evolution during late compression and early expansion were studied. In particular, this work aims to analyze Turbulent Kinetic Energy (TKE) spatial and temporal evolution influence on heat transfer coefficient. The analysis is based on experimental TKE maps derived from Particle Image Velocimetry (PIV) data. For the heat transfer coefficient estimation a modified Woschni correlation has been used. Results from several injection strategies and a reference motored case have been analyzed. It has been found that injection strategy has a considerable influence on the TKE field and hence on heat transfer coefficient evolution. (C) 2017 Elsevier Ltd. All rights reserved.The authors gratefully acknowledge the Swedish Energy Agency and the Competence Center for Combustion Processes KCFP. The authors also would like to acknowledge that part of the work has been partially funded by the Spanish Government under the grant "Jose Castillejo" (JC2015/0036). Research leading to this work has also receive funding from Universitat Politecnica de Valencia through the FPI program.Tanov, S.; Pachano-Prieto, LM.; Andersson, Ö.; Wang, Z.; Richter, M.; Pastor, JV.; García-Oliver, JM.... (2018). Influence of spatial and temporal distribution of Turbulent Kinetic Energy on heat transfer coefficient in a light duty CI engine operating with Partially Premixed Combustion. Applied Thermal Engineering. 129:31-40. https://doi.org/10.1016/j.applthermaleng.2017.10.006S314012

Investigation of late-cycle soot oxidation using laser extinction and in-cylinder gas sampling at varying inlet oxygen concentrations in diesel engines

[EN] This study focuses on the relative importance of O-2 and OH as oxidizers of soot during the late cycle in diesel engines, where the soot oxidation is characterized in an optically accessible engine using laser extinction measurements. These are combined with in-cylinder gas sampling data from a single cylinder engine fitted with a fast gas-sampling valve. Both measurements confirm that the in-cylinder soot oxidation slows down when the inlet concentration of O-2 is reduced. A 38% decrease in intake O-2 concentration reduces the soot oxidation rate by 83%, a non-linearity suggesting that O-2 in itself is not the main soot oxidizing species. Chemical kinetics simulations of OH concentrations in the oxidation zone and estimates of the OH-soot oxidation rates point towards OH being the dominant oxidizer.The authors gratefully acknowledge the Swedish Energy Agency, the Competence Center for Combustion Processes KCFP (Project number 22485-3), and the competence center METALUND funded by FORTE for financially supporting this research. The authors acknowledge Volvo AB for providing the gas-sampling valve and personally Jan Eismark (Volvo AB) and Mats Bengtsson (Lund University) for their technical support.Gallo, Y.; Malmborg, VB.; Simonsson, J.; Svensson, E.; Shen, M.; Bengtsson, P.; Pagels, J.... (2017). Investigation of late-cycle soot oxidation using laser extinction and in-cylinder gas sampling at varying inlet oxygen concentrations in diesel engines. Fuel. 193:308-314. https://doi.org/10.1016/j.fuel.2016.12.013S30831419

Development and Application of Laser Techniques for Studying Fuel Dynamics and NO Formation in Engines

Development and application of some laser techniques for the study of engine combustion are presented. The investigations mainly cover two aspects: fuel dynamics and formation of NO. Fuel dynamics is one of the most central problems in engine design since many performance parameters are affected by it; emission formation, efficiency, drivability etc. The studies include cycle-resolved measurements of short-circuiting losses in two-stroke engines, mixture stratification in a direct-injection gasoline engine, and mixture formation in DI diesel engines. NO is one of the most harmful pollutants from combustion and is subject to tightening emission regulations. Absolute NO concentrations were determined in a near-production spark ignition engine, and a two-photon detection scheme was evaluated for use in practical applications. Furthermore, an alternative fuel for diesel engines, DME, was investigated with respect to optical properties and fuel properties when used in DI diesel engines. One of the major advantages of using laser diagnostics in this context is their unique capability of providing simultaneous multi-point information in two dimensions, e.g. on species concentrations. They also feature superior spatial and temporal resolution and are, almost always, non-intrusive. The use of probe sampling to determine species concentrations yields lower resolution in space and time and inevitably disturbs flows and temperature fields

Performance of new and aged injectors with and without fuel additives in a light duty diesel engine

Two sets of diesel injectors are tested in combination with common fuel additives in a multi-cylinder light-duty diesel engine. One set consists of new injectors and the other is aged by over 100,000 km use in a vehicle. Four fuels are tested with these injector sets to investigate the impact of fuel additives on combustion and emission characteristics. The results show that the aged injectors consistently deliver larger quantities of fuel for a given injection strategy, leading to a higher power output and deviating emissions. This is hypothesized to be due to drift in the injector actuating characteristics. The fuels tested are a baseline diesel quality, and blends of this fuel with three additives: a cetane number improver (2-ethylhexyl nitrate), a soot reducer (tripropylene-glycol monomethyl ether), and a flow improver consisting of quaternary ammonium salts. At the selected low and medium load operating conditions, these additives had a smaller effect on the emissions than the injector ageing, the most notable effect being that TPGME reduces the soot emissions even at the oxygen-rich conditions studied here. These studies will be followed by optical investigations of the in-cylinder effects on spray and combustion characteristics