Premixed charge compression ignition (PCCI) is one of the most promising combustion strategies re fPoCrCinItecronmalbcuosmtiobnusitsioanbelengtoineresailniztehevefurytulroew,ssinocoet rssue 1 2 3 4 and nitric oxide emissions. PCCI is a low temper- P ature combustion (LTC) strategy, which combines the efficiency of a Diesel and the low particulate emission of an Otto engine. BDC TDC
To achieve low emissions of NOx and particu- Timing (CA) late matter (PM) the combustion should be decou- Figure 1: Engine cycle with pressure peak at top dead pled from the injection of the fuel to avoid a spray center (TDC). PCCI concepts classification by injection that burns predominantly in diffusion mode. This timing range. 1=port fuel injection, before bottom dead decoupling makes the combustion process difficult center (BDC), 2= early DI, 3=conventional diesel comto control. When allowing a certain degree of strat- bustion, 4=late DI ification in the cylinder, control over the combustion process by injection timing is partly restored. and extend the operating range. This will be in
Although premixed, the air-fuel mixture is not vestigated by measuring velocities, concentrations
completely homogeneous, as in a homogeneous and temperatures both in an optical engine and in
charge compression ignition (HCCI) engine. By a constant volume high pressure cell.
premixing the charge, combustion in both HCCI
and PCCI is dominated by chemical kinetics [
The lower rate of heat release extends the op- gine is used to investigate stratification under runerating range from low load to medium or even full ning engine conditions. The engine test setup conload. Temperature stratification has the highest in- sists of a one cylinder optically accessible heavy fluence on the rate of heat release and pressure duty engine, based on a Ricardo Proteus test enrise rate and extends the high-load operating limit gine and a DAF MX NA cylinder head, driven by [2]. an electrical motor. A cross-section of the setup
A classification of PCCI combustion concepts is is shown in figure 2. The piston is elongated and given in figure 1. In this figure the pressure inside the upper part of the liner and piston bottom are the engine is plotted as a function of time and dif- both made of sapphire. Via a mirror, positioned unferent classes of PCCI injection timing are shown. der 45 degrees, optical access to the combustion Port fuel injection is only applied for gasoline fueled chamber is obtained. The hydraulic cylinder can PCCI engines and takes place before bottom dead be lowered, allowing easy access to the combuscenter (BDC). For early direct injection (DI) PCCI tion chamber. The engine specifications in Table 1 combustion, collision of injected fuel spray against show fixed valve timings and variable compression the cylinder liner, so-called wall-wetting, is one of ratios (CR). The compression ratio can be changed the main hurdles to overcome. quickly between measurements by positioning the
In this project we are focussing on injecting to- cylinder head on a different height, thereby changwards the end of the early DI regime, around 30 ing the volume at TDC.
CAD BTDC. The objective of this project is to in- The Eindhoven high pressure cell setup (EHPC) vestigate the influence of charge stratification on can be seen in figure 3. Its core is a cubically PCCI combustion to reduce the heat release rate shaped combustion chamber produced through spark erosion inside a stainless steel cube. The holes on each side of the combustion chamber can ∗ be fitted either with a window or with a similarly shaped metal plug. Engine conditions towards the
Corresponding author: r.p.c.zegers@tue.nl Towards Clean Diesel Engines, TCDE 2009
45◦ mirror cently, with crank angle resolution obtained from ensemble averaging of single shot measurements [3]. Time-resolved PIV measurements are in progress, to obtain a data set for comparison with end of the compression stroke are simulated by CFD results. The engine will be modified further burning a lean pre-charge of gaseous fuel, and the to apply PCCI combustion by implementing more walls of the cell are heated up electrically to sim- flexible fuel injection equipment. ulate realistic wall temperatures and prevent water Tracer PLIF will be used to measure tempercondensation on the windows. This is the so-called ature and concentrations gradients (which is now pre-combustion technique. Once the desired con- being prepared at Radboud University of Nijmegen ditions are reached the diesel fuel spray is injected. [4], possibly combined with a phosphoresce techTo determine the right moment of injection, the de- nique for temperature gradient detection. The cay of average pressure at a certain condition is phosphoresce technique is developed in cooperarecorded. tion with Lund institute of Technology. Methodology Acknowledgements
Stratification control will in practice have to rely This project is funded by the Dutch technolon sophisticated injection strategies. The main fo- ogy foundation STW, involving the following induscus point of this research is the use of (multiple) di- trial partners: Shell Global Solutions, DAF Trucks, rect injections as a method to create stratification. Wa¨rtsila¨ and TNO Automotive. Their contribution For this project some restrictions are applied on the is greatly acknowledged. amount of engine operating points, summarized in table 2.
A first elaborate set of PIV (Particle Image Velocimetry) measurements has been performed re[2] Sjoberg M., Dec J.E., and Cernansky N.P. Potential of thermal stratification and combustion retard for reducing pressure-rise rates in HCCI engines based on multi-zone modeling and experiments. SAE 2005-01-0113, 2005. [3] Zegers R.P.C., Meyden T.J. van der, Luijten C.C.M., Dam N.J., Baert R.S.G., and Goey L.P.H. de. Crank angle resolved flow field characterization of a heavy-duty (PCCI) engine. Proceedings of the European Combustion Meeting, 2009. [4] Mannekutla J.R., Huijben J.C.C.M., Donkerbroek A.J., Vliet A.P. van, Gerritsen L., Dam N.J., and Meulen J.J. ter. Two-line OH thermometry during PCCI combustion. Towards Clean Diesel Engines symposium, 2009.