The negative impact of transport on climate has led to incentives to increase the amount of renewable fuels used in internal combustion engines (ICEs). Oxygenated, liquid biofuels are promising alternatives, as they exhibit similar combustion behaviour to gasoline. In this article, the effect of the different biofuels on engine efficiency, combustion propagation and emissions of a gasoline-optimised direct injected spark ignited (DISI) engine were evaluated through engine experiments. The experiments were performed without any engine hardware modifications. The investigated fuels are gasoline, four alcohols (methanol, ethanol, n-butanol and iso-butanol) and one ether (MTBE). All fuels were tested at two speed sweeps at low and mid load conditions, and a spark timing sweep at low load conditions. The oxygenated biofuels exhibit increased efficiencies, even at non-knock-limited conditions. At lower loads, the oxygenated fuels decrease CO, HC and NOx emissions. However, at mid load conditions, decreased volatility of the alcohols leads to increased emissions due to fuel impingement effects. Methanol exhibited the highest efficiencies and significantly increased burn rates compared to the other fuels. Gasoline exhibited the lowest level of PN and PM emissions. N-butanol and iso-butanol show significantly increased levels of particle emissions compared to the other fuels

The transport sector is one of the main sources of greenhouse gas emissions.Replacing fossil fuels with renewable fuels can help reduce the impact oftransportation on the climate. Liquid, oxygenated biofuels show great potentialas a replacement in spark-ignited engines, as they exhibit similarcombustion behavior to gasoline, and are compatible with existing infrastructure.This thesis aims to expand the knowledge on how oxygenated fuelsaffect emissions and performance in direct-injected spark-ignited (DISI) engines.Experiments on a gasoline optimised DISI engine at low and mid loadconditions, were conducted to establish how these fuels affect engine efficiency,combustion propagation, and emissions. A thorough investigationon how the particle emissions change with different fuels was also performed.The research evaluated five different oxygenated fuels in comparison to gasoline:ethanol, methanol, n-butanol, iso-butanol, and methyl tert-butyl ether.The oxygenated fuels all increased engine efficiency, even at low loads wherethe engine was not knock limited. The most significant increase in efficiencywas observed for methanol, with up to 12% improvement in indicated thermalefficiency compared to gasoline. At low loads all oxygenated fuels decreasedthe emissions of unburned hydrocarbons, carbon monixde and nitrogenoxides. The results at mid load conditions show that fuels with lowvolatility will increase these emissions. The findings also indicate that fuelvolatility will have a more significant impact on the particle emissions levelsthan fuel oxygen content. This effect is more pronounced at lower enginespeeds and higher engine loads.This thesis work reveals great potential to use liquid, oxygenated biofuelsin DISI engines to decrease transport-associated carbon dioxide emissions.Even without engine modifications, oxygenated fuels yield improved engineefficiency compared to gasoline. Optimized injection for fuels with decreasedvolatility is needed to reduce emissions at higher engine loads.

Transportsektorn är en stor bidragande faktor till utsläppen av växthusgaser. Därmed kan ersättningen av fossila bränslen med förnyelsebara bränslen bidra till att reducera transportsektorns inverkan på klimatet. Flytande oxygenerade biobränslen visar stor potential som ersättningsalternativ till bensin, eftersom de har liknande förbränningsegenskaper och är kompatibla med nuvarande infrastruktur. Målet med denna avhandling är att bidra till en ökad kunskap om hur oxygenerade bränslen påverkar emissioner och prestanda i direktinsprutade gnisttända (DISI) motorer. Experiment på en bensinoptimerad DISI motor utfördes för att fastställa hur dessa bränslen påverkar motorns verkningsgrad, flamutbredning, samt utsläppsnivåerna av emissioner. En grundlig undersökning av hur partikelemissionerna förändrades med olika bränslen genomfördes också. Fem olika oxygenarade bränslen undersöktes, och jämfördes med bensin: etanol, metanol, n-butanol, iso-butanol, och metyl tert-butyl eter.

Alla de oxygenerade bränslena ökade motorns verkninsgrad, även vid lägre laster då motorn inte var begränsad av knack. Störst öking av verkningsgraden uppvisades då metanol användes som bränsle. Metanol ökade den indikerade termiska verkningsgraden med upp till 12% jämfört med bensin. Vid låga laster minskade emissionerna av oförbrända kolväten, kolmonoxid och kväveoxider vid användning av oxygenerade bränslen jämfört mot bensin. Medan vid medelhög last så ökade emissionerna för de bränslen som har låg flyktighet. De experimentella resultaten visar att bränslets flyktighet har högre inverkan på mängden partiklar som motorn släpper ut än bränslets syrehalt. Denna effekt är tydligare vid lägre varvtal och högre laster. Den här avhandlingen visar att användningen av flytande, oxygenerade bränslen i DISI motorer visar stor potential till att minska transportsektorns koldioxid utsläpp. De oxygenerade bränslena ökade motorns verkningsgrad i jämförelse med bensin, även optimering av motorn till dessa bränslen. Optimering av bränsleinsprutningen krävs för att minska emissionerna vid högre laster för bränslen med lägre flyktighet än bensin.

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. However, PN shows a significant increase for ethanol, especially at low engine speed due to a deterioration in the evaporation, mixture formation and air entrainment of ethanol. A majority of the emitted particles exhibit particle sizes below 23 nm, wherein the highest numbers occurred below 10 nm. At steady-state operation, no clear difference was observed between the diluted and undiluted measurements. On the contrary, a significant difference is detected between the undiluted and diluted measurements of ethanol at idle. These observations could indicate a greater significance of dilution at lower exhaust gas temperatures and mass flow rates or when a large number of nucleation mode particles are emitted from the engine.

The utilisation of internal combustion engines is one of the main causes of particle emissions in urban areas. As the interest for the utilisation of biofuels increases, it is important to understand their effect on particle number emissions. In this paper, the particle size distribution and the particle number emissions from a gasoline-optimised direct-injected spark-ignited (DISI) engine are investigated. The effects of five different biofuel alternatives on these emissions were evaluated and compared to gasoline. The utilisation of the high-resolution, high-temperature ELPI+ enabled undiluted measurements of the particle size distribution down to 6 nm, without extensive cooling of the engine exhaust. Contrary to other studies, the results show that the particle number emissions for the three measured cut-off sizes (23, 10 and 7 nm) increased with the utilisation of oxygenated biofuels. The results indicate that the decreased volatility and energy density of the alcohols has a more significant impact on the particle formation in a DISI engine than the increased oxygen content of these fuels.

The increased rates of research on complex fuel blends in engine applications poses a need for more efficient and accurate fuel blending processes in engine laboratories. Making the fuel blending process automatic, effective, accurate and flexible saves time, storage space and cost without compromising the tests of future fuel alternatives. To meet these requirements, an automatic fuel blending system, following a sequential batch process, was designed and tested for engine laboratory application.The fuel blending system was evaluated in terms of functionality, safety, accuracy and repeatability. The functionality and safety was evaluated through a risk analysis. Whereas, the accuracy and repeatability of the system was investigated through blend preparation tests. The results show that the minimum fuel mass limitation of the system is 0.5 kg. This allows for blends with fuel ratios as low as 7 vol-% to be prepared by the system. The mean relative errors for all tested fuels are below 5% by mass, enabling a wide range of fuels to be used in the system. The absolute error in fuel ratio is 0.5 vol-% or less. In addition, the relative error in fuel ratio of the prepared blends is below 4% for all but one of the tested blends. Moreover, the system can prepare all of the tested fuel blends in 5 minutes.

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. Three groups of oxygenated liquid biofuels were investigated in this review: alcohols, ethers and furans. While the investigated alcohols showcase properties associated with increased engine efficiencies (such as higher chemical knock resistance, greater charge cooling and faster laminar flame speeds). They also pose the challenge of greater fuel consumption due to lower energy densities than gasoline. Ethers and furans, on the other hand are favored by current engine designs as they exhibit properties (such as the energy density) closer to gasoline alongside increased chemical knock resistance.

The compiled data summarizes the possibilities to improve efficiency and fuel economy for biofuel and binary blends in SI engines. However, the results also, show that some of the trends are more complex than anticipated. The effect of biofuels on combustion speed, regulated emissions and exhaust temperatures are not proven to be as self-evident as reported in previous studies. Results on multiple blends with focus on the effect of blending on properties would help improve the picture of the effect of future fuels on SI combustion.