Search Results

Diesel Dual Fuel, DDF, is a concept which promises the possibility to utilize CNG/biogas in a compression ignition engine maintaining a high compression ratio, made possible by the high knock resistance of methane, and the resulting benefits in thermal efficiency associated with Diesel combustion. Presenter Fredrik K�nigsson, AVL Sweden

In order for premixed methane diesel dual fuel engines to meet current and future legislation, the emissions of unburned hydrocarbons must be reduced while high efficiency and high methane utilization is maintained. This paper presents an experimental investigation into the effects of in cylinder air motion, swirl and tumble, on the emissions, heat transfer and combustion characteristics of dual fuel combustion at different air excess ratios. Measurements have been carried out on a single cylinder engine equipped with a fully variable valve train, Lotus AVT. By applying different valve lift profiles for the intake valves, the swirl was varied between 0.5 and 6.5 at BDC and the tumble between 0.5 and 4 at BDC. A commercial 1D engine simulation tool was used to calculate swirl number and tumble for the different valve profiles. Input data for the simulation software was generated using a steady-state flow rig with honeycomb torque measurements.

Emissions of unburned methane are the Achilles heel of premixed gas engines whether they are spark ignited or diesel pilot ignited. If the engine is operated lean, lower temperatures prevail in the combustion chamber and several of the mechanisms behind the hydrocarbon emissions are aggravated. This paper presents an experimental investigation of the contribution from combustion chamber crevices and quenching to the total hydrocarbon emissions from a diesel-methane dual fuel engine at different operating conditions and air excess ratios. It is shown that the sensitivity to a change in topland crevice volume is greater at lean conditions than at stoichiometry. More than 70% of hydrocarbon emissions at air excess ratios relevant to operation of lean burn engines can be attributed to crevices.

The purpose of an engine controller is to fulfil emission, consumption and driveability requirements and to be able to fully utilize the potential of a modern engine with its high degree of freedom, the complexity of the controller becomes very high. The long calibration time, the complex architecture, the limited I/O and intellectual property make production controllers difficult to use in a research environment, where there is often a need to change the functionality in order to test new concepts. This is why many universities develop their own engine controller, which in many cases is only used for one project, why a lot of valuable research time is lost in developing the basic controller. This paper describes an open source engine controller for rapid prototyping to be used freely at the universities in Sweden for their research and education purposes.

Diesel Dual Fuel, DDF, is a concept which promises the possibility to utilize CNG/biogas in a compression ignition engine maintaining a high compression ratio, made possible by the high knock resistance of methane, and the resulting benefits in thermal efficiency associated with diesel combustion. A series of tests has been carried out on a single-cylinder lab engine, equipped with a modern common rail injection system supplying the diesel fuel and two gas injectors, placed in the intake runners. One feature of port-injected Dual Fuel is that full diesel functionality is maintained, which is of great importance when bringing the dual fuel technology to market. The objective of the study was to characterize and investigate the potential for dual fuel combustion utilizing all degrees of freedom available in a modern diesel engine. Increased diesel pilot proved efficient at reducing NOx emissions at low λ.

Engine simulation has traditionally been an instrument for the early phase of engine design in order to choose the optimal compromise between the different requirements, such as cost, packaging, performance and fuel consumption. However, the problem has somewhat changed from an engine design to an engine calibration and function development task, as new technologies increase the degree of freedom to such an extent that it is almost impossible to find the optimal setting in the test bench. The purpose of the model is to be used as a Model-In-the-Loop model for offline simulation and debugging during the algorithm development phase of the engine controller. It can also be used during the rapid prototyping calibration phase as the amount of measurements needed for the model is relatively small. From the measurements, simulation can rapidly be executed to find a calibration setting which is in the correct ballpark.

Diesel Dual Fuel, DDF, is a concept where a combination of methane and diesel is used in a compression ignited engine, maintaining the high compression ratio of a diesel engine with the resulting benefits in thermal efficiency. One benefit of having two fuels on board the vehicle is the additional degree of freedom provided by the ratio between the fuels. This additional degree of freedom enables control of combustion phasing for combustion modes such as Homogenous Charge Compression Ignition, HCCI, and Partly Premixed Compression Ignition, PPCI. These unconventional combustion modes have great potential to limit emissions at light load while maintaining the low pumping losses of the base diesel engine. A series of tests has been carried out on a single cylinder lab engine, equipped with a modern common rail injection system supplying the diesel fuel and two gas injectors, placed in the intake runners.

Diesel Dual Fuel, DDF, is a concept where a combination of methane and diesel is used in a compression ignited engine, maintaining the high compression ratio of a diesel engine with the resulting benefits in thermal efficiency. Attention has recently been drawn to the fact that the tip of the diesel injector may reach intolerable temperatures. The high injector tip temperatures in the DDF engine are caused by the reduction in diesel flow through the injector. For dual fuel operation, as opposed to diesel, high load does not necessarily imply a high flow of diesel through the injector nozzle. This research investigated the factors causing high injector tip temperatures in a DDF engine and the underlying mechanisms which transfer heat to and from the injector tip. Parameter sweeps of each influential parameter were carried out and evaluated. In addition to this, a simple and useful model was constructed based on the heat balance of the injector tip.

Nozzle coking in diesel engines has received a lot of attention in recent years. High temperature in the nozzle tip is one of the key factors known to accelerate this process. In premixed CNG-diesel dual fuel, DDF, engines a large portion of the diesel fuel through the injector is removed compared to regular diesel operation. This can result in very high nozzle temperatures. Nozzle hole coking can therefore be expected to pose a significant challenge for DDF operation. In this paper an experimental study of nozzle coking has been performed on a DDF single cylinder engine. The objective was to investigate how the rate of injector nozzle hole coking during DDF operation compares to diesel operation. In addition to the nozzle tip temperature, the impact of other parameters on coking rate was also of interest. Start of injection, λ, diesel substitution ratio and common rail pressure were varied in two levels starting from a common baseline case, resulting in a total of 10 operating cases.