Study on low temperature heat release of partially premixed combustion in a heavy duty engine for real-time applications

European and US emission legislation on diesel compression ignition engines has pushed for the development of new types of combustion concepts to reduce hazardous pollutants and increase fuel efficiency. Partially premixed combustion (PPC) has been proposed as one solution to future restrictions on emissions while providing high gross indicated efficiency. The conceptual idea is that the time for the mixing between fuel and air will be longer when ignition delay is increased by addition of high amounts of exhaust gas recirculation (EGR). Increased air-fuel mixing time will lead to lower soot emissions and the high EGR rates will reduce both NOx emissions and combustion flame temperature, which decreases the overall heat transfer. Previous research in heavy-duty gasoline PPC has mostly focused on emissions and efficiency at low and medium load in single-cylinder engines. In this paper a Volvo D13 heavy-duty single-stage VGT engine with a newly developed Wave piston was run at medium and high engine load with a variation in fuel injection pressure. The Wave piston was specifically designed to enhance air-fuel mixing and increase combustion velocity. Two fuels were used in the experiments, PRF70 and Swedish MK1 diesel. Soot-NOx trade-off, combustion characteristics and efficiency were compared for both fuels at 1000 and 2000 Nm engine torque. The results show that at high load the combustion behavior with respect to rate of heat release and heat transfer is very similar between the fuels and no major difference in indicated efficiency could be observed. Peak gross indicated efficiencies were reported to be around 49 % for both fuels at 1000 Nm and slightly above 50 % at 2000 Nm. The new Wave piston made it possible to obtain 1 g/kWh engine-out NOx emissions while still complying with Euro VI legislation for particulate emissions. Soot emissions were generally lower for PRF70 compared to MK1 diesel. We could also conclude that gas exchange performance is a major issue when running high load PPC where high Λ and EGR is required. The single-stage VGT turbocharger could not provide sufficient boost to keep Λ above 1.3 at high EGR rates. This penalized combustion efficiency and soot emissions when reaching Euro VI NOx emission levels (0.3–0.5 g/kWh).

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Effect of split fuel injection on heat release and pollutant emissions in partially premixed combustion of PRF70/air/EGR mixtures

Applied Energy ◽

10.1016/j.apenergy.2015.03.058 ◽

2015 ◽

Vol 149 ◽

pp. 283-296 ◽

Cited By ~ 27

Author(s):

F. Zhang ◽

R. Yu ◽

X.S. Bai

Keyword(s):

Heat Release ◽

Fuel Injection ◽

Premixed Combustion ◽

Pollutant Emissions ◽

Partially Premixed Combustion ◽

Partially Premixed

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Combustion stratification study of partially premixed combustion using Fourier transform analysis of OH* chemiluminescence images

International Journal of Engine Research ◽

10.1177/1468087417740270 ◽

2017 ◽

Vol 19 (10) ◽

pp. 1024-1035 ◽

Cited By ~ 2

Author(s):

Mohammad Izadi Najafabadi ◽

Bart Somers ◽

Bengt Johansson ◽

Nico Dam

Keyword(s):

Heat Release ◽

High Speed ◽

Spatial Information ◽

Fourier Transforms ◽

Combustion Regime ◽

Premixed Combustion ◽

Two Dimensional ◽

Spatial Frequencies ◽

Partially Premixed Combustion ◽

Partially Premixed

A relatively high level of stratification (qualitatively: lack of homogeneity) is one of the main advantages of partially premixed combustion over the homogeneous charge compression ignition concept. Stratification can smooth the heat release rate and improve the controllability of combustion. In order to compare stratification levels of different partially premixed combustion strategies or other combustion concepts, an objective and meaningful definition of “stratification level” is required. Such a definition is currently lacking; qualitative/quantitative definitions in the literature cannot properly distinguish various levels of stratification. The main purpose of this study is to objectively define combustion stratification (not to be confused with fuel stratification) based on high-speed OH* chemiluminescence imaging, which is assumed to provide spatial information regarding heat release. Stratification essentially being equivalent to spatial structure, we base our definition on two-dimensional Fourier transforms of photographs of OH* chemiluminescence. A light-duty optical diesel engine has been used to perform the OH* bandpass imaging on. Four experimental points are evaluated, with injection timings in the homogeneous regime as well as in the stratified partially premixed combustion regime. Two-dimensional Fourier transforms translate these chemiluminescence images into a range of spatial frequencies. The frequency information is used to define combustion stratification, using a novel normalization procedure. The results indicate that this new definition, based on Fourier analysis of OH* bandpass images, overcomes the drawbacks of previous definitions used in the literature and is a promising method to compare the level of combustion stratification between different experiments.

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