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Alcohol-based fuels are a viable alternative to fossil fuels for powering vehicles. As a drop-in fuel, an oxygenated fuel blend containing the C8 alcohol 2-ethylhexanol (isomer of octanol), hydrotreated vegetable oil (HVO) and rapeseed methyl ester (RME) can reduce soot and NOx emissions whilst maintaining engine performance. However, fuel injection strategy significantly affects combustion and hence has been investigated with a view to reducing emissions whilst maintaining engine efficiency. In a single cylinder light-duty compression ignition research engine, the effect of different injection strategies (main, main/post, double pre/main, double pre/main/post injection) and EGR levels (0%, 19%) on specifically NOx, soot emissions and particle size distribution was investigated for three different fuels: fossil diesel fuel, HVO and the oxygenated blend. The blend was designed to have diesel-like combustion properties (cetane number of 52) and had an oxygen content of 5.4% by mass.

Spray characteristics of fossil Diesel fuel, hydrotreated vegetable oil (HVO) and two oxygenated fuel blends were studied to elucidate the combustion process. The fuels were studied in an optically accessible high-pressure/high-temperature chamber under non-combusting (623 K, 4.69 MPa) and combusting (823 K, 6.04 MPa) conditions. The fuel blends contained the long-chain alcohol 2-ethylhexanol (EH), HVO and either 20 vol.% Diesel or 7 vol.% rapeseed methyl ester (RME) and were designed to have a Diesel-like cetane number (CN). Injection pressures were set to 120 MPa and 180 MPa and the gas density was held constant at 26 kg/m3. Under non-combusting conditions, shadow imaging revealed the penetration length of the liquid and vapor phase of the spray. Under combusting conditions, the lift-off length and soot volume fraction were measured by simultaneously recording time-resolved two-dimensional laser extinction, flame luminosity and OH* chemiluminescence images.

The effects of using n-butanol, n-octanol, fossil Diesel, hydrotreated vegetable oil (HVO), and blends of these fuels on spray penetration, flame and soot characteristics were investigated in a high-pressure high-temperature constant volume combustion chamber designed to mimic a heavy duty Diesel engine. Backlight illumination was used to capture liquid and vapor phase spray images with a high-speed camera. The flame lift-off length (LOL) and ignition delay were determined by analyzing OH* chemiluminescence images. Laser extinction diagnostics were used to measure the spatially and temporally resolved soot volume fraction. The spray experiments were performed by injecting fuels under non-combusting (623 K) and combusting (823 K) conditions at a fixed ambient air density of 26 kg/m3. A Scania 0.19 mm single straight hole injector and Scania XPI common rail fuel supply system were used to produce injection pressures of 120 MPa and 180 MPa.

Global warming driven by “greenhouse gas” emissions is an increasingly serious concern of both the public and legislators. A potentially potent way to reduce these emissions and conserve fossil fuel resources is to use n-butanol, iso-butanol or octanol (2-ethylhexanol) from renewable sources as alternative fuels in diesel engines. The effects of adding these substances to diesel fuel were therefore tested in a single-cylinder heavy duty diesel engine operated using factory settings. These alcohols have better calorific values, flash points, lubricity, cetane numbers and solubility in diesel than shorter-chain alcohols. However, they have lower cetane numbers than diesel, so either hydrotreated vegetable oil (HVO) or Di-tertiary-butyl peroxide (DTBP) was added to the diesel-alcohol mixtures to generate blends with the same Cetane Number (CN) as diesel.

The free piston internal combustion engine used in conjunction with a linear alternator offers an interesting choice for use in hybrid vehicles. The linear motion of the pistons is directly converted to electricity by the alternator, and the result is a compact and efficient energy converter that has only one moving part. The movement of the pistons is not prescribed by a crank mechanism, but is the result of the equilibrium of forces acting on the pistons, and the engine will act like a mass-spring system. This feature is one of the most prominent advantages of the FPE (Free Piston Engine), as the lack of mechanical linkage gives means of varying the compression ratio in simple manners, without changing the hardware of the engine. By varying the compression ratio, it is also it possible to run on a multitude of different fuels and to use HCCI (Homogeneous Charge Compression Ignition) combustion.