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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.

Modern spark-ignited (SI) engines offer excellent emission reduction when operated with a stoichiometric mixture and a three-way catalytic converter. A challenge with stoichiometric compared to diluted operation is the knock propensity due to the high reactivity of the mixture. This limits the compression ratio, thus reducing engine efficiency and increasing exhaust temperature. The current work evaluated a model of conditions at inlet valve closing (IVC) and top dead center (TDC) for steady state operation. The IVC temperature model is achieved by a cycle-to-cycle resolved residual gas fraction estimator. Due to the potential charge cooling effect from methanol, a method was proposed to determine the fraction of fuel sourced from a wall film. Determining the level of charge cooling is important as it heavily impacts the IVC and TDC temperatures.

Stoichiometric operation of a Port Fueled Injection (PFI) Spark-Ignited (SI) engine with a three-way catalytic converter offers excellent CO2 reduction when run on renewable fuel. The main drawbacks with stoichiometric operation are the increased knock propensity, high exhaust temperature and reduced efficiency. Knock is typically mitigated with a reactive knock controller, with retarded ignition timing whenever knock is detected and the timing then slowly advanced until knock is detected again. This will cause some cycles to operate with non-ideal ignition timing. The current work evaluates the possibility to predict knock using the measured and modelled temperatures at Inlet Valve Closing (IVC) and Top Dead Center (TDC). Feedback effects are studied beyond steady state operation by using induced ignition timing disturbances.

Alcohols offer high resistance to autoignition which is necessary to attain the required load in heavy duty (HD) spark ignition (SI) engines. Dilution increases thermal efficiency and reduces propensity to autoignition making it an important combustion strategy. Reliable and robust prediction at increased dilution is necessary to support development of high efficiency spark ignition engines and the transition to renewable fuels. A previous experimental study demonstrated 25 bar gross IMEPg for ethanol and methanol at λ=1.4 excess air ratio and over 48% indicated efficiency at λ=1.6 on a single cylinder engine. Based on this dataset, a semi-predictive model (SITurb) was fitted for a range of excess air ratios and engine loads. With the default model, poor accuracy was observed above λ=1.4. Ignition delay was incorrectly predicted at λ=1.6 and λ=1.8.

In this paper, a High-Temperature Electrical Low-Pressure Impactor (HT-ELPI+) was used to measure particles from a light-duty direct injected spark ignited (DISI) engine fueled with gasoline and ethanol. The HT-ELPI+ measured volatile and non-volatile particle emissions down to 6 nm without the need for dilution. Particle emissions were measured at four operating points while sweeping the end of injection, and at idle operation. The total particle number (PN) and particle size distribution (number and mass) for both non-volatile and volatile emissions were measured with the HT-ELPI+ and compared to the measured PN using two 71.4 times diluted Condensation Particle Counters (CPCs) with two different cut-off sizes, with 23 nm and 7 nm cut-off, respectively. The results show an increase in particle emissions in terms of particle mass and total particle number for ethanol compared to gasoline. The difference in soot mass emissions is small between the fuels.

Diffusive combustion of direct injected ethanol is investigated in a heavy-duty single cylinder engine for a broad range of operating conditions. Ethanol has a high potential as fossil fuel alternative, as it provides a better carbon footprint and has more sustainable production pathways. The introduction of ethanol as fuel for heavy-duty compression-ignition engines can contribute to decarbonize the transport sector within a short time frame. Given the resistance to autoignition of ethanol, the engine is equipped with two injectors mounted in the same combustion chamber, allowing the simultaneous and independent actuation of the main injection of pure ethanol and a pilot injection of diesel as an ignition source. The influence of the dual-fuel injection strategy on ethanol ignition, combustion characteristics, engine performance and NOx emissions is evaluated by varying the start of injection of both fuels and the ethanol-diesel ratio.

Knock in heavy duty (HD) spark ignition (SI) engines is exacerbated by a large bore diameter and a higher flame travel distance. An increase in turbulence close to TDC can improve combustion speed and reduce knock through low residence time for end gas auto-ignition. Since HD SI engines are usually derived from diesel engines, it is common to have a swirl motion that does not dissipate into turbulence. To increase flame speed and limit knock, squish can be used to produce turbulence close to TDC. In this study, two different piston bowl geometries are examined: the re-entrant and quartette. The influence of squish area on turbulence production by these piston geometries were investigated using motored simulations in AVL FIRE. The effect of increased turbulence on knock reduction was analyzed using a calibrated 1D GT-Power model of a HD SI engine and the performance improvement was estimated.

The introduction of renewable alcohols as fuels for heavy-duty engines may play a relevant role for the reduction of the carbon footprint of the transport sector. The direct injection of ethanol as main fuel and diesel as pilot fuel in the engine combustion chamber through two separate injectors may allow good combustion controllability over the entire engine operating range by targeting diffusive combustion. Closed-cycle combustion simulations have been carried out using AVL FIRE coupled to AVL TABKIN for the implementation of the Flamelet Generated Manifold (FGM) chemistry reduction technique in order to investigate the influence of the injection system geometry and the injection strategy of pure ethanol and diesel fuel on ignition characteristics and combustion at different operating conditions.

Global warming and climate change have led to a greater interest in the implementation of biofuels in internal combustion engines. In spark ignited engines, biofuels have been shown to improve efficiency and knock resistance while decreasing emissions of unburned hydrocarbons, carbon monoxide and particles. This study investigates the effect of biofuels on SI engine combustion through a graphical compilation of previously reported results. Experimental data from 88 articles were used to evaluate the trends of the addition of different biofuels in gasoline. Graphs illustrating engine performance, combustion phasing and emissions are presented in conjunction with data on the physiochemical properties of each biofuel component to understand the observed trends. Internal combustion engines have the ability to handle a wide variety of fuels resulting in a broad range of biofuel candidates.

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.

Spark Ignition (SI) engines operating on stoichiometric mixtures can employ a simple three-way catalyst as after-treatment to achieve low tailpipe emissions unlike diesel engines. This makes heavy duty (HD) SI engines an attractive proposition for low capital cost and potentially low noise engines, if the power density and efficiency requirement could be met. Specific torque at low speeds is limited in SI engines due to knock. In HD engines, the higher flame travel distances associated with higher bore diameters exacerbates knock due to increased residence time of the end gas. This report reviews the challenges in developing HD SI engines to meet current diesel power density. It also focuses on methods to mitigate them in order to achieve high thermal efficiency while running on stoichiometric condition. High octane renewable fuels are seen as a key enabler to achieve the performance level required in such applications.

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.