Fundamental Study of Diesel-Piloted Natural Gas Direct Injection Under Different Operating Conditions

2018 ◽  
Author(s):  
Georg Fink ◽  
Michael Jud ◽  
Thomas Sattelmayer
Keyword(s):  
Natural Gas ◽  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Soot Formation ◽  
Direct Injection ◽  
Combustion Process ◽  
Operating Conditions ◽  
Gas Jet ◽  
Ignition And Combustion

Natural gas as an alternative fuel in engine applications substantially reduces both pollutant and greenhouse gas emissions. High pressure dual fuel direct injection of natural gas and Diesel pilot has the potential to minimize methane slip from gas engines and increase the fuel flexibility, while retaining the high efficiency of a Diesel engine. Speed and load variations as well as various strategies for emission reduction entail a wide range of different operating conditions. The influence of these operating conditions on the ignition and combustion process is investigated on a rapid compression expansion machine. By combining simultaneous Shadowgraphy and OH* imaging with heat release rate analysis, an improved understanding of the ignition and combustion process is established. At high temperatures and pressures the reduced pilot ignition delay and lift-off length minimize the effect of natural gas jet entrainment on pilot mixture formation. A simple geometrical constraint was found to reflect the susceptibility for misfiring. At the same time natural gas ignition is delayed by the early pilot ignition close to the injector tip. The shape of heat release is only marginally affected by the operating conditions and mainly determined by the degree of premixing at the time of gas jet ignition. Luminescence from the sooting natural gas flame is generally only detected after the flame extends across the whole gas jet at peak heat release rate. Termination of gas injection at this time was confirmed to effectively suppress soot formation, while a strongly sooting pilot seems to intensify soot formation within the natural gas jet.

Fundamental Study of Diesel-Piloted Natural Gas Direct Injection Under Different Operating Conditions

2019 ◽  
Vol 141 (9) ◽  
Author(s):  
Georg Fink ◽  
Michael Jud ◽  
Thomas Sattelmayer
Keyword(s):  
Natural Gas ◽  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Soot Formation ◽  
Direct Injection ◽  
Combustion Process ◽  
Operating Conditions ◽  
Gas Jet ◽  
Ignition And Combustion

Natural gas as an alternative fuel in engine applications substantially reduces both pollutant and greenhouse gas emissions. High pressure dual fuel (HPDF) direct injection of natural gas and diesel pilot has the potential to minimize methane slip from gas engines and increase the fuel flexibility, while retaining the high efficiency of a diesel engine. Speed and load variations as well as various strategies for emission reduction entail a wide range of different operating conditions. The influence of these operating conditions on the ignition and combustion process is investigated on a rapid compression expansion machine (RCEM). By combining simultaneous shadowgraphy (SG) and OH* imaging with heat release rate analysis, an improved understanding of the ignition and combustion process is established. At high temperatures and pressures, the reduced pilot ignition delay and lift-off length minimize the effect of natural gas jet entrainment on pilot mixture formation. A simple geometrical constraint was found to reflect the susceptibility for misfiring. At the same time, natural gas ignition is delayed by the early pilot ignition close to the injector tip. The shape of heat release is only marginally affected by the operating conditions and mainly determined by the degree of premixing at the time of gas jet ignition. Luminescence from the sooting natural gas flame is generally only detected after the flame extends across the whole gas jet at peak heat release rate. Termination of gas injection at this time was confirmed to effectively suppress soot formation, while a strongly sooting pilot seems to intensify soot formation within the natural gas jet.

Influence of the Spatial and Temporal Interaction Between Diesel Pilot and Directly Injected Natural Gas Jet on Ignition and Combustion Characteristics

2017 ◽  
Author(s):  
Georg Fink ◽  
Michael Jud ◽  
Thomas Sattelmayer
Keyword(s):  
Natural Gas ◽  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Combustion Process ◽  
Gas Jet ◽  
Injection Timing ◽  
Release Rates ◽  
Temporal Interaction ◽  
The Impact

In this paper, pilot-ignited high pressure dual-fuel (HPDF) combustion of a natural gas jet is investigated on a fundamental basis by applying two separate single-hole injectors to a rapid compression expansion machine (RCEM). A Shadowgraphy system is used for optical observations, and the combustion progress is assessed in terms of heat release rates. The experiments focus on the combined influence of injection timing and geometrical jet arrangement on the jet interaction and the impact on the combustion process. In a first step, the operational range for successful pilot self-ignition and transition to natural gas jet combustion is determined, and the restricting phenomena are identified by analyzing the shadowgraph images. Within this range, the combustion process is assessed by evaluation of ignition delays and heat release rates. Strong interaction is found to delay or even prohibit pilot ignition, while it facilitates a fast and stable onset of the gas jet combustion. Furthermore, it is shown that the heat release rate is governed by the time of ignition with respect to the start of natural gas injection — as this parameter defines the level of premixing. Evaluation of the time of gas jet ignition within the operability map can therefore directly link a certain spatial and temporal interaction to the resulting heat release characteristics. It is finally shown that controlling the heat release rate through injection timing variation is limited for a certain angle between the two jets.

Simultaneous Imaging of OH* Chemiluminescence and Flame Luminosity of Diesel and Biodiesel Spray Combustion

2011 ◽  
Author(s):  
Ji Zhang ◽  
Tiegang Fang
Keyword(s):  
Ambient Temperature ◽  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Soot Formation ◽  
Combustion Process ◽  
Spray Combustion ◽  
Chemiluminescence Intensity ◽  
High Temperature Reaction ◽  
The Impact

The research on the spray combustion of diesel and biodiesel is vital to the understanding of emission formation and optimal utilization of fuel. This paper studies the biodiesel and diesel spray combustion in a constant volume chamber under different simulated diesel engine conditions. The ambient temperature at fuel injection varied from 800K to 1200K, while the ambient oxygen concentration was maintained at 21%. Simultaneous high speed imaging of OH* chemiluminescence and flame luminosity was employed to visualize the whole combustion process. Heat release rate was analyzed based on the measured combustion pressure. The apparent heat release rate analysis shows that biodiesel has a shorter ignition delay time than diesel, and biodiesel has a smaller cumulative heat release value due to its lower heating value. The overlaying image of OH* chemiluminescence and flame luminosity clearly identifies the high temperature reaction regions and soot formation regions. The line-of-sight images agree with the published observation that the hydroxyl radical is formed on the lean side of the flame edge. Decreasing ambient temperature greatly reduces the OH* chemiluminescence intensity of the diesel combustion, while the impact is smoother and milder for biodiesel combustion. Biodiesel shows a significantly lower level of flame luminosity than diesel under all conditions. These combined observations lead to a speculation that the soot oxidation process may serve as an important contributor to OH* chemiluminescence intensity for late stage combustion, and biodiesel shows a tendency to produce less soot than diesel under the investigated conditions.

Influence of the Spatial and Temporal Interaction Between Diesel Pilot and Directly Injected Natural Gas Jet on Ignition and Combustion Characteristics

2018 ◽  
Vol 140 (10) ◽  
Author(s):  
Georg Fink ◽  
Michael Jud ◽  
Thomas Sattelmayer
Keyword(s):  
Natural Gas ◽  
Heat Release ◽  
Combustion Process ◽  
Optical Observations ◽  
Gas Jet ◽  
Injection Timing ◽  
Ignition And Combustion ◽  
Temporal Interaction ◽  
Operational Range ◽  
The Impact

In this paper, pilot-ignited high pressure dual-fuel combustion of a natural gas jet is investigated on a fundamental basis by applying two separate single-hole injectors to a rapid compression expansion machine (RCEM). A Shadowgraphy system is used for optical observations, and the combustion progress is assessed in terms of heat release rates (HRRs). The experiments focus on the combined influence of injection timing and geometrical jet arrangement on the jet interaction and the impact on the combustion process. In a first step, the operational range for successful pilot self-ignition and transition to natural gas jet combustion is determined, and the restricting phenomena are identified by analyzing the shadowgraph images. Within this range, the combustion process is assessed by evaluation of ignition delays and HRRs. Strong interaction is found to delay or even prohibit pilot ignition, while it facilitates a fast and stable onset of the gas jet combustion. Furthermore, it is shown that the HRR is governed by the time of ignition with respect to the start of natural gas injection—as this parameter defines the level of premixing. Evaluation of the time of gas jet ignition within the operability map can therefore directly link a certain spatial and temporal interaction to the resulting heat release characteristics. It is finally shown that controlling the HRR through injection timing variation is limited for a certain angle between the two jets.

scholarly journals Heat release rate and emissions regimes of stratified pilot-ignited direct-injection natural gas combustion

2021 ◽  
pp. 146808742110469
Author(s):  
Jeremy Rochussen ◽  
Gordon McTaggart-Cowan ◽  
Patrick Kirchen
Keyword(s):  
Natural Gas ◽  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Internal Combustion Engines ◽  
Direct Injection ◽  
Injection Timing ◽  
Heavy Duty ◽  
Wide Range ◽  
The Impact

Natural gas (NG) is an attractive fuel for heavy-duty internal combustion engines because of its potential for reduced CO2, particulate, and NOX emissions and lower cost of ownership. Pilot-ignited direct-injected NG (PIDING) combustion uses a small pilot injection of diesel to ignite a main direct injection of NG. Recent studies have demonstrated that increased NG premixing is a viable strategy to increase PIDING indicated efficiency and further reduce particulate and CO emissions while maintaining low CH4 emissions. However, it is unclear how the combustion strategies relate to one another, or where they fit within the continuum of NG stratification. The objective of this work is to present a systematic evaluation of pilot combustion, NG combustion, and emissions behavior of stratified-premixed PIDING combustion modes that span from fully-premixed to non-premixed conditions. A sweep of the relative injection timing, [Formula: see text], of NG and pilot diesel was performed in a heavy-duty PIDING engine with [Formula: see text] = 140–220 bar, [Formula: see text] = 0.47–0.71, and a constant NG energy fraction of 94%. Apparent heat release rate and emissions analyses identified interactions between the pilot fuel and NG, and qualitatively characterized the impact of NG stratification on combustion and emissions. Changes in the [Formula: see text] resulted in six distinct PIDING combustion regimes, for all considered injection pressures and equivalence ratios: (i) RIT-insensitive premixed, (ii) stratified-premixed (early-cycle injection), (iii) NG jet impingement transition, (iv) stratified-premixed (late-cycle injection), (v) variable premixed fraction, and (vi) minimally-premixed. Parametric definitions for the bounds of each regime of combustion were valid for the wide range of [Formula: see text] and [Formula: see text] investigated, and are expected to be relevant for other PIDING engines, as previously identified regimes agree with those identified here. This conceptual framework encompasses and validates the findings of previous stratified PIDING investigations, including optimal ranges of operation that provide significantly increased efficiency and lower emissions of incomplete combustion products.

Predicting Ignition and Combustion of a Pilot Ignited Natural Gas Jet Using Numerical Simulation Based on Detailed Chemistry

2017 ◽  
Author(s):  
Michael Jud ◽  
Georg Fink ◽  
Thomas Sattelmayer
Keyword(s):  
Natural Gas ◽  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Direct Injection ◽  
Dual Fuel ◽  
Pressure Curve ◽  
Detailed Chemistry ◽  
Dual Fuel Combustion ◽  
Good Agreement

In this paper, a multidimensional computational fluid dynamics (CFD) model coupled with detailed chemistry calculations was used to analyze dual-fuel combustion based on high pressure direct injection of natural gas. The main focus was to analyze the capability of predicting pressure curve and heat release rate (HRR) for different injection strategies. Zero-dimensional homogeneous constant volume reactor calculations were used to select a reaction mechanism for the temperature range below 800 K. As the best-performing mechanism, the Chalmers mechanism was chosen. To validate the numerical model, the setup was first split into a single gas injection and a single Diesel injection. They were validated individually using shadowgraphs obtained from a Rapid Compression Expansion Machine (RCEM). Diesel ignition timing and position in the combustion chamber were close to experimental results. Gas direct injection showed good agreement with regard to penetration and mixing. In the dual-fuel setup, the injection timing of natural gas was varied to create a first case with mainly diffusive combustion and a second case with mainly premixed combustion of natural gas. For both setups good agreement with pressure curve and heat release rate were achieved. A qualitative comparison of shadowgraphs with the density field highlights the important points to predict dual-fuel combustion.

Development of a Real-Time NOx Prediction Model Based on Heat Release Analysis in a Direct-Injection Diesel Engine

2013 ◽  
Vol 136 (3) ◽  
Author(s):  
Dong Wang ◽  
Chao Zhang
Keyword(s):  
Diesel Engine ◽  
Prediction Model ◽  
Heat Release ◽  
Real Time ◽  
Heat Release Rate ◽  
Release Rate ◽  
Direct Injection ◽  
Operating Conditions ◽  
Nox Emissions ◽  
Direct Injection Diesel Engine

A prediction model, which describes linear relationship between the nitrogen oxides (NOx) emissions and the in-cylinder heat release rate in a direct-injection diesel engine, was developed through numerical simulations. A modified KIVA-3 V code was used to calculate NOx formations and to conduct heat release analyses in a direct-injection diesel engine under different operating conditions. The numerical simulation results indicated that the NOx formation amount was related to both the magnitude and the timing of the peak heat release rate in each engine cycle. Based on the above observations, a control-oriented dynamic NOx model was constructed and then implemented into a feedback emission control system on a small diesel engine. A new parameter—combustion acceleration—was proposed in this research to describe the intensity of the premixed combustion. Experimental work was also conducted to measure the real-time in-cylinder pressure at each crank-angle when the engine was running and the heat release rate was calculated instantaneously to control an exhaust gas recirculation (EGR) valve. The experimental results showed that the proposed NOx prediction model was effective in controlling NOx emissions under high rpm conditions.

Effects of Ambient Temperature and Oxygen Concentration on Soot Evolution in Diesel Spray Combustion

Volume 4 ◽  
2004 ◽  
Author(s):  
Yi Xu ◽  
Chia-Fon F. Lee
Keyword(s):  
Ambient Temperature ◽  
Heat Release ◽  
Oxygen Concentration ◽  
Heat Release Rate ◽  
Release Rate ◽  
Soot Formation ◽  
Premixed Combustion ◽  
Ambient Oxygen ◽  
Lower Heat ◽  
Soot Measurement

A newly developed Forward Illumination Light Extinction (FILE) soot measurement technique was applied in a constant volume spray chamber to study the effects of ambient temperature and oxygen concentration on soot evolution in diesel combustion. The FILE technique with the capability of two-dimensional time-resolved quantitative soot measurement provides the much-needed information to investigate the soot formation mechanism. The ambient temperatures of 1200K, 1000K and 800K were tested to study the temperature effects on soot formation. A decrease of ambient temperature results in a longer ignition delay, which promotes a larger premixed combustion zone combining with higher heat release rates. The change of ambient temperature from 1200K to 800K increases the fuel portion burnt in the premixed combustion period. At 800K, combustion is dominated by the premixed combustion and much less soot is formed. Diesel combustion with 21% and 15% ambient oxygen concentration was also studied. With lower ambient oxygen concentration, the combustion process is basically not changed, but expands into a longer time span with a lower heat release rate. The lower heat release rate results in a lower flame temperature, which benefits the NOx emission control. However, with about the same amount of soot within the flame, and much longer soot life, soot has more chance to escape to the exhaust.

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