Search Results

A viable option to reduce global warming related to internal combustion engines is to use renewable fuels, for example methanol. However, the risk of knocking combustion limits the achievable efficiency of SI engines. Hence, most high load operation is run at sub-optimal conditions to suppress knock. Normally the fuel is a limiting factor, however when running on high octane fuels such as methanol, other factors also become important. For example, oil droplets entering the combustion chamber have the possibility to locally impact both temperature and chemical composition. This may create spots with reduced octane number, hence making the engine more prone to knock. Previous research has confirmed a connection between oil droplets in the combustion chamber and knock. Furthermore, previous research has confirmed a connection between oil droplets in the combustion chamber and exhaust particle emissions.

Sustainable fuels can help to decrease carbon dioxide emissions in road transportation compared to standard fossil fuels. The most common sustainable fuels used today in heavy-duty applications are biodiesel and hydrogenated vegetable oil (HVO). Biodiesel and HVO are known as drop-in fuels since they are fuels that can be blended with standard diesel. However, due to changes in the chemical properties when the fuels are mixed, solubility problems in terms of precipitates may be formed. These insolubilities can lead to deposits in the fuel system, e.g., blocked fuel filters and internal injector deposits, and thus driveability problems. This study is a part of a project where the goal is to study the processes that cause the formation of deposits inside the injectors in heavy-duty vehicles. The deposits inside the injectors are known as internal diesel injector deposits (IDID).

A method developed in SAE 2019-01-0058 to correct for deviations from quasi-steady exhaust valve flow is implemented on a single-cylinder GT-Power model and the effects on pumping work and blowdown pulse characteristics are investigated. The valve flow area is always reduced compared to the reference quasi-steady case. It decreases with higher pressure ratios over the valve and increases with higher engines speeds. The reduced flow area increases pumping work with load and engine speed, though primarily with engine speed. The magnitude of the blowdown pulse is reduced and the peak is shifted to a later crank angle.

Increasing demands for more efficient engines and stricter legislations on exhaust emissions require more accurate control of the engine operating parameters. Engine control is based on sensors monitoring the condition of the engine. Numerous sensors, in a complex control context, increase the complexity, the fragility and the cost of the system. An alternative to physical sensors are virtual sensors, observers used to monitor parameters of the engine thus reducing both the fragility and the production cost but with a slight increase of the complexity. In the current paper a virtual intake manifold cylinder port pressure sensor is presented. The virtual sensor is based on a compressible flow model and on the pressure signal of the intake manifold pressure sensor. It uses the linearized pressure coefficient approach to keep vital performance behaviors while still conserving calibration effort and embedded system memory.

To conduct system level studies on internal combustion engines reduced order models are required in order to keep the computational load below reasonable limits. By its nature a reduced order model is a simplification of reality and may introduce modeling errors. However what is of interest is the size of the error and if it is possible to reduce the error by some method. A popular system level study is gas exchange and in this paper the focus is on the exhaust valve. Generally the valve is modeled as an ideal nozzle where the flow losses are captured by reducing the flow area. As the valve moves slowly compared to the flow the process is assumed to be quasi-steady, i.e. interpolation between steady-flow measurements can be used to describe the dynamic process during valve opening. These measurements are generally done at low pressure drops, as the influence of pressure ratio is assumed to be negligible.

Gaseous methane fuel for internal combustion engines have proved to be a competitive source of propulsion energy for heavy duty truck engines. Using biogas can even reduce the carbon footprint of the truck to near-zero levels, creating fully environmentally friendly transport. Gas engines have already been on the market and proved to be a popular alternative for buses and waste transport. However, for long haulage these gas engines have not been on par with the equivalent diesel engines. To improve the power and efficiency of EURO VI gas engines running stoichiometrically, a direct way forward is adding more boost pressure and spark advance in combination with more EGR to mitigate knock. Using in-cylinder turbulence to achieve higher mixing rate, the fuel can still be combusted efficiently despite the increased fraction of inert gases.

Clean combustion is one of the inherent benefits of using a high methane content fuel, natural gas or biogas. A single carbon atom in the fuel molecule results, to a large extent, in particle-free combustion. This is due to the high energy required for binding multiple carbon atoms together during the combustion process, required to form soot particles. When scaling up this process and applying it in the internal combustion engine, the resulting emissions from the engine have not been observed to be as particle free as the theory on methane combustion indicates. These particles stem from the combustion of engine oil and its ash content. One common practice has been to lower the ash content to regulate the particulate emissions, as was done for diesel engines. For a gas engine, this approach has been difficult to apply, as the piston and valvetrain lubrication becomes insufficient.

On-engine surge detection could help in reducing the safety margin towards surge, thus allowing higher boost pressures and ultimately low-end torque. In this paper, experimental data from a truck turbocharger compressor mounted on the engine is investigated. A short period of compressor surge is provoked through a sudden, large drop in engine load. The compressor housing is equipped with knock accelerometers. Different signal treatments are evaluated for their suitability with respect to on-engine surge detection: the signal root mean square, the power spectral density in the surge frequency band, the recently proposed Hurst exponent, and a closely related concept optimized to detect changes in the underlying scaling behavior of the signal. For validation purposes, a judgement by the test cell operator by visual observation of the air filter vibrations and audible noises, as well as inlet temperature increase, are also used to diagnose surge.

Improving turbocharger performance to increase engine efficiency has the potential to help meet current and upcoming exhaust legislation. One limiting factor is compressor surge, an air flow instability phenomenon capable of causing severe vibration and noise. To avoid surge, the turbocharger is operated with a safety margin (surge margin) which, as well as avoiding surge in steady state operation, unfortunately also lowers engine performance. This paper investigates the possibility of detecting compressor surge with a conventional engine knock sensor. It further recommends a surge detection algorithm based on their signals during transient engine operation. Three knock sensors were mounted on the turbocharger and placed along the axes of three dimensions of movement. The engine was operated in load steps starting from steady state. The steady state points of operation covered the vital parts of the engine speed and load range.

Diesel engine manufacturers strive towards further efficiency improvements. Thus, reducing in-cylinder heat losses is becoming increasingly important. Understanding how location, thermal insulation, and engine operating conditions affect the heat transfer to the combustion chamber walls is fundamental for the future reduction of in-cylinder heat losses. This study investigates the effect of a 1mm-thick plasma-sprayed yttria-stabilized zirconia (YSZ) coating on a piston. Such a coated piston and a similar steel piston are compared to each other based on experimental data for the heat release, the heat transfer rate to the oil in the piston cooling gallery, the local instantaneous surface temperature, and the local instantaneous surface heat flux. The surface temperature was measured for different crank angle positions using phosphor thermometry.

In one dimensional engine simulation software, flow losses over complex geometries such as valves and ports are described using flow coefficients. It is generally assumed that the pressure ratio over the valve has a negligible influence on the flow coefficient. However during the exhaust valve opening the pressure difference between cylinder and port is large which questions the accuracy of this assumption. In this work the influence of pressure ratio on the exhaust valve flow coefficient has been investigated experimentally in a steady-flow test bench. Two cylinder heads, designated A and B, from a Heavy-Duty engine with different valve shapes and valve seat angles have been investigated. The tests were performed with both exhaust valves open and with only one of the two exhaust valves open. The pressure ratio over the exhaust port was varied from 1.1:1 to 5:1. For case A1 with a single exhaust valve open, the flow coefficient decreased significantly with pressure ratio.

Due to demanding legislation on exhaust emissions for internal combustion engines and increasing fuel prices, automotive manufacturers have focused their efforts on optimizing turbocharging systems. Turbocharger system control optimization is difficult: Unsteady flow conditions combined with not very accurate compressor maps make the real time turbocharger rotational speed one of the most important quantities in the optimization process. This work presents a methodology designed to obtain the turbocharger rotational speed via vibration analysis. Standard knock sensors have been employed in order to achieve a robust and accurate, yet still a low-cost solution capable of being mounted on-board. Results show that the developed method gives an estimation of the turbocharger rotational speed, with errors and accuracy acceptable for the proposed application. The method has been evaluated on a heavy duty diesel engine.