Rsg Rik Baert

Experimental Demonstration of RCCI in Heavy-Duty Engines using Diesel and Natural Gas

Premixed combustion concepts like PCCI and RCCI have attracted much attention, since these concepts offer possibilities to reduce engine out emissions to a low level, while still achieving good efficiency. Most RCCI studies use a combination of a high-cetane fuel like diesel, and gasoline as low-cetane fuel. Limited results have been published using natural gas as low-cetane fuel; especially full scale engine results. This study presents results from an experimental study of diesel-CNG RCCI operation on a 6 cylinder, 8 l heavy duty engine with cooled EGR. This standard Tier4f diesel engine was equipped with a gas injection system, which used single point injection and mixed the gaseous fuel with air upstream of the intake manifold. For this engine configuration, RCCI operating limits have been explored. In the 1200-1800 rpm range, RCCI operation with Euro-VI engine out NOx and soot emissions was achieved between 2 and 9 bar BMEP without EGR. Corresponding hydrocarbon levels were high, but exhaust temperature levels hold promise for a suitable reduction through catalytic aftertreatment. Thermal efficiency was comparable to or better than diesel operation. In the load ranges tested, gas Methane Number (MN) variations between 70 and 100 have only a small effect on RCCI performance.

Oxygenated fuels for clean heavy-duty diesel engines

For diesel engines, changing the fuel composition is an alternative route towards achieving lower emission levels. The potential of oxygenated fuels to significantly reduce particulate matter emissions has already been demonstrated earlier. In this study, this research has been extrapolated towards lower emission levels. Exhaust gas recirculation (EGR) was applied to a modern EURO-3-type HD diesel engine. Tests were done at different engine working points, with EGR-levels and start of fuel delivery timings set to give NOx emissions between 3.5 and 2.0g/kWh with regular diesel fuel. Fourteen blends of a low-sulphur diesel fuel respectively of a gas-to-liquid synthetic diesel fuel with different oxygenates were tested. The corresponding fuel matrix covers a range of fuel oxygen mass fractions up to 15%. Results are presented and the impact of fuel oxygen mass fraction and Cetane Number are analysed and compared with results from previous research.

Experimental validation of extended NO and Soot model for advanced HD Diesel Engine Combustion

A computationally efficient engine model is developed based on an extended NO emission model and state-of-the-art soot model. The model predicts exhaust NO and soot emission for both conventional and advanced, high-EGR (up to 50%), heavy-duty DI diesel combustion. Modeling activities have aimed at limiting the computational effort while maintaining a sound physical/chemical basis. The main inputs to the model are the fuel injection rate profile, in-cylinder pressure data and trapped in-cylinder conditions together with basic fuel spray information. Obtaining accurate values for these inputs is part of the model validation process which is thoroughly described. Modeling results are compared with single-cylinder as well as multi-cylinder heavy-duty diesel engine data. NO and soot level predictions show good agreement with measurement data for conventional and high-EGR combustion with conventional timing.

Study of Turbulent Flow Structures of a Practical Steady Engine Head Flow Using Large-Eddy Simulations

The prediction performance of two computational fluid dynamics codes is compared to each other and to experimental data of a complex swirling and tumbling flow in a practical complex configuration. This configuration consists of a flow in a production-type heavy-duty diesel engine head with 130-mm cylinder bore. One unsteady Reynolds-averaged Navier-Stokes (URANS)-based simulation and two large-eddy simulations (LES) with different inflow conditions have been performed with the KIVA-3V code. Two LES with different resolutions have been performed with the FASTEST-3D code. The parallelization of the this code allows for a more resolved mesh compared to the KIVA-3V code. This kind of simulations gives a complete image of the phenomena that occur in such configurations, and therefore represents a valuable contribution to experimental data. The complex flow structures gives rise to an inhomogeneous turbulence distribution. Such inhomogeneous behavior of the turbulence is well captured by the LES, but naturally damped by the URANS simulation. In the LES, it is confirmed that the inflow conditions play a decisive role for all main flow features. When no particular treatment of the flow through the runners can be made, the best results are achieved by computing a large part of the upstream region, once performed with the FASTEST-3D code. If the inflow conditions are tuned, all main complex flow structures are also recovered by KIVA-3V. The application of upwinding schemes in both codes is in this respect not crucial.

Experimental Study into a Hybrid PCCI/CI Concept for Next-Generation Heavy-Duty Diesel Engines

This paper presents the first results of an experimental study into a hybrid combustion concept for next-generation heavy-duty diesel engines. In this hybrid concept, at low load operating conditions, the engine is run in Pre-mixed Charge Compression Ignition (PCCI) mode, whereas at high load conventional CI combustion is applied. This study was done with standard diesel fuel on a flexible multi-cylinder heavy-duty test platform. This platform is based on a 12.9 liter, 390 kW heavy-duty diesel engine that is equipped with a combination of a supercharger, a two-stage tubocharging system and lowpressure and highpressure EGR circuitry. Furthermore, Variable Valve Actuation (VVA) hardware is installed to have sufficient control authority. Dedicated pistons, injector nozzles and VVA cam were selected to enable PCCI oombustion for a late DI injection strategy, free of wall-wetting problems. The decision to use a multicylinder configuration instead of a single cylinder research engine was taken because this allows to assess the impact of limitations in operating range of current turbocharger equipment and that of cylinder interaction. It also allowed to assess control issues relevant for future production engines. First results are shown for four low load ESC operating points, Injection timing, EGR rate and effective compression ratio are varied to find suitable PCCI operating conditions with this equipment. The effect of these control parameters on combustion phasing, heat release, emissions (NOx, HC, CO, smoke), and fuel consumption is presented. Similar trade-offs are determined for conventional CI combustion at higher loads. From the experimental results, it is concluded that PCCI combustion is succcessfuly realized up to 25% load, corresponding to 5.6 bar BMEP. Further optimization of TC matching and combustion is needed to improve PCCI fuel efficiency and especially high load CI operation.

Optimization of Operating Conditions in the Early Direct Injection Premixed Charge Compression Ignition Regime

Early Direct Injection Premixed Charge Compression Ignition (EDI PCCI) is a widely researched combustion concept, which promises soot and CO2 emission levels of a spark-ignition (SI) and compression-ignition (CI) engine, respectively. Application of this concept to a conventional CI engine using a conventional CI fuel faces a number of challenges. First, EDI has the intrinsic risk of wall-wetting, i.e. collision of fuel against the combustion chamber periphery. Second, engine operation in the EDI regime is difficult to control as auto-ignition timing is largely decoupled from fuel injection timing. In dual-mode PCCI engines (i.e. conventional DI at high loads) wall-wetting should be prevented by selecting appropriate (most favorable) operating conditions (EGR level, intake temperature, injection timing-strategy etc.) rather than by redesign of the engine (combustion chamber shape, injector replacement etc.). This paper presents the effects of EGR concentration, intake temperature, intake pressure, injection timing, injection pressure and fuel temperature on engine performance and emission behavior in EDI PCCI mode. In addition, several minor adjustments to the conventional injector nozzle are investigated. Wall-wetting and engine performance are characterized by the measured emissions (smoke and unburned hydrocarbons) and in-cylinder pressure (CA50 and IMEP). The main contribution of this paper is to investigate the cumulative effects on engine performance and emissions, unburnt hydrocarbons (HC) in particular, of various known measures designed to address wall-wetting. All experiments have been performed at low load (~ 3-4 bar IMEP) and at an engine speed of 1200 RPM, using a modified 6-cylinder 12.6 liter heavy-duty DI DAF XE 355 C engine. Experiments are conducted in one dedicated cylinder, which is equipped with a stand-alone fuel injection system, EGR circuit and air compressor, fuelled with commercial diesel fuel (EN590).

SCR-only concept for heavy-duty Euro-VI applications

To meet Euro VI emission targets for heavy-duty applications, truck manufacturers concentrate on Exhaust Gas Recirculation (EGR) and its combination with urea-based Selective Catalytic Reduction (SCR). TNO developed a concept that opens the route for an alternative solution which relies on SCR as the main technology for NOx abatement. This concept offers potential fuel benefits in combination with low impact on engine design and cooling equipment. Together with Haldor Topsoe, Yara and Grundfos, TNO examined the achievable NOx emission reduction on an engine dynamometer.

On The Impact of the Ideal Gas Assumption to High-Pressure Combustion Phenomena in Engines

The effect of the ideal gas law assumption on auto-ignition and NOx-formation in a rapid compression machine is studied. For both processes the simulations are compared to a reference simulation using a Redlich-Kwong equation-of-state based on the critical properties of all constituents. Auto-ignition is studied for several n-heptane/air mixtures and the results show that the ideal gas assumption can impose large deviations. However, only marginal differences (< 7%) appear if the pressure history is used. A simplified theory is presented that explains these observations. For the case of NOx-formation similar observations can be made. Large deviations from the full simulation occur for the case of a prescribed pressure and volume history (≈ 100%). This, however, is mainly due to the fact that in engine like applications NOx concentrations never reach their equilibrium value. Equilibrium values only differ by a maximum of 20%.

The effect of the strain rate on PAH/soot formation in laminar counterflow diffusion flames

PAH/soot has been modeled in two types of laminar counterflow diffusion flames using a detailed reaction mechanism based on the sectional method. The two flames differ mainly by their fuel type: ethylene versus benzene. Their sensitivity to the strain rate is analyzed with respect to the total PAH/soot mass density and number density, as well as the particle size distribution function. A strong sensitivity to these parameters has been confirmed, in line with experimental data. The chemical production rates of the first two moments of the PAH/soot particle size distribution functions are found to be a moderate function of the strain rate. These observations are explained by a scaling analysis. The current application of the detailed mechanism in different diffusion type of flames gives valuable information on its width of applicability, and can be used for the optimization of the model parameters.

Application of PIV to characterise the Flow-Phenomena of a Heavy-Duty Cylinder Head on a Stationary Flow-Bench

With modern heavy-duty diesel engines the design of the inlet ports in the cylinder head is such that some degree of swirling motion is induced in the engine cylinders during intake. This swirling motion is mostly characterized using a stationary flow bench. In such a flow bench, a dummy cylinder is used instead of the cylinder in the engine. In this situation there is no moving piston, the air can flow out of the open end of the dummy cylinder.