Martin Muinos

RCCI of synthetic kerosene with PFI of N-butanol-combustion and emissions characteristics

In this study, the combustion and emissions characteristics of Reactivity Controlled Compression Ignition (RCCI) obtained by direct injection (DI) of S8 and port fuel injection (PFI) of n-butanol were compared with RCCI of ultra-low sulfur diesel #2 (ULSD#2) and PFI of n-butanol at 6 bar indicated mean effective pressure (IMEP) and 1500 rpm. S8 is a synthetic paraffinic kerosene (C6–C18) developed by Syntroleum and is derived from natural gas. S8 is a Fischer-Tropsch fuel that contains a low aromatic percentage (0.5 vol. %) and has a cetane number of 63 versus 47 of ULSD#2. Baselines of DI conventional diesel combustion (CDC), with 100% ULSD#2 and also DI of S8 were conducted. For both RCCI cases, the mass ratio of DI to PFI was set at 1:1. The ignition delay for the ULSD#2 baseline was found to be 10.9 CAD (1.21 ms) and for S8 was shorter at 10.1 CAD (1.12 ms). In RCCI, the premixed charge combustion has been split into two regions of high temperature heat release, an early one BTDC from ignition of ULSD#2 or S8, and a second stage, ATDC from n-butanol combustion. RCCI with n-butanol increased the NOx because the n-butanol contains 21% oxygen, while S8 alone produced 30% less NOx emissions when compared to the ULSD#2 baseline. The RCCI reduced soot by 80–90% (more efficient for S8). However, S8 alone showed a considerable increase in soot emissions compared with ULSD#2. The indicated thermal efficiency was the highest for the ULSD#2 and S8 baseline at 44%. The RCCI strategies showed a decrease in indicated thermal efficiency at 40% ULSD#2-RCCI and 42% and for S8-RCCI, respectively.S8 as a single fuel proved to be a very capable alternative to ULSD#2 in terms of combustion performance nevertheless, exhibited higher soot emissions that have been mitigated with the RCCI strategy without penalty in engine performance.Copyright

NVH of RCCI With DI ULSD and PFI With 50% N-Butanol

The noise of diesel engines is dependent upon numerous factors such as: load, speed, fuel injection strategies and fuel type, design of the piston, piston-pin and cylinder and their tolerances, bearings, valves and rocker arm clearances, and designs of the manifolds.In this study, engine sound and vibrations analysis have been conducted using two types of fueling and combustion strategies: classical ULSD combustion and the new RCCI with n-butanol injected in the intake manifold. The analyses add to the understanding of the influence of combustion characteristics’ effect on mechanical noise and vibrations throughout the engine’s operating cycle.The sound and vibration signals were both analyzed in the frequency and angle domain spectrum. Overall NVH spectrum from ULSD combustion was compared to that of RCCI with 50% by mass PFI of n-butanol (the 50% remaining ULSD fuel was directly injected).Frequency analyses were performed using the FFT and CPB methods with Bruel & Kjaer’s Pulse sound and vibrations analysis software. Angle domain analyses were performed, referencing 0 CAD as TDC in combustion.The engine tests were conducted at 1500 rpm and 4 bar IMEP. The COV of IMEP for DI ULSD and RCCI were 2.4 and 2.2, respectively. The correlations between sound, three dimensional vibration levels, and timings were found for: pressure gradients from combustion process, intake and exhaust valve actuations and gas exchange, and piston slap on the cylinder liner.The measurements were extracted and analyzed, and the results determined that virtually all the noise and vibration values pertinent to RCCI were lower than those of ULSD classical combustion.Copyright

Indirect Combustion Technology With Renewable Non-Edible Transesterified Oil Feedstock

This investigation focused on the combustion and performance of an indirect injection (IDI) diesel engine powered by a non-edible biodiesel blend, Brassica Carinata. This oilseed has become an attractive non-edible feedstock for biodiesel in the United States, given potential agronomical advantages. A small bore, single cylinder IDI engine was run at 2000 rpm and 5.5 bar indicated mean effective pressure (IMEP) using ultra-low sulfur diesel #2 (ULSD#2) and compared with C50, a 50% Carinata biodiesel-ULSD#2 blend (by mass). The apparent heat release for C50 reached a maximum of 22.04 J/deg which was 6.3 % lower and peaked 1.80 CAD before ULSD#2. The radiation and convection heat fluxes had similar maximum values of 0.62 MW/m2 and 1.34 MW/m2, respectively. The brake specific fuel consumption (BSFC) of C50 was 211.05 g/kWh, which was 9% higher than for ULSD#2. The mechanical efficiency was maintained relatively constant at 55% while the indicated thermal efficiency of the engine reached 59%. Both fuels produced similar nitrogen oxide (NOx) emissions with ULSD#2 and C50 producing 2.29 g/kWh and 2.23 g/kWh, respectively. The results indicate that the IDI engine can optimally work with concentrations up to 50% biodiesel.Copyright

Combustion Performance, Noise, and Vibrations of an IDI Engine Fueled With Carinata Biofuel

The performance of an indirect injection engine fueled with a biodiesel blend was investigated at 2400 rpm and 6 bar IMEP. The single cylinder experimental engine was run using C50 and compared to a ULSD#2 baseline. Brassica carinata oilseed was studied as it can potentially provide improvements for existing fuel infrastructures. Cylinder pressure data for C50 showcased a lower heat release and slightly higher injection pressure due to higher SMD. Brake specific fuel consumption was 6% higher for C50 given the characteristic LHV of biodiesel. Vibrations and sound measurements were analyzed in the frequency and crank angle domain through the Bruel & Kjaer PULSE software platform. Sound pressure correlations were determined according to the piston normal force on the cylinder liner, intake and exhaust valve timing, and operating speed. For both fuels, vibrations parallel to the cylinder axis reached 1.6–2.6 m/s2 in the 40–120 Hz frequency range; noise reached 80–87 dB at frequencies of 1–4 kHz. C50 produced 0.4 g/kWh fewer NOx emissions which correlate to a lower maximum bulk gas temperature and richer air-fuel ratio. The average ringing intensity was 0.05 MW/m2 for both fuels due to a comparable pressure rise rate. When the engine was run with C50, the reference mechanical efficiency of 53% was effectively maintained. This offers validation for further implementation of blended biodiesel fuel in IDI engines.Copyright

Aircraft Turbine Sound and Vibrations Signatures for a Synthetic Kerosene Fuel

Aero gas turbine engines generate high levels of sound across a wide frequency spectrum. The total sound energy produced by the engine is composed of multiple thermodynamic sources, including the air intake, combustion, and exhaust. The focus in this research is the investigation of the combustion noise. The combustion process is complex and dependent upon the properties of the fuel being used. Different fuels have different reaction and evaporation times, indicating that the noise may increase or decrease between each type of fuel. Fuels can affect how a turbine produces a sound output that will eventually be perceived by the human ear. In this study, two fuels were used in the operation of an aircraft gas turbine in the Georgia Southern University’s Aerospace Engine Laboratory. The SR-30 gas turbine is capable of operating at a maximum speed of 80,000 rpm, produce a maximum thrust of 40 lbf, has a pressure ratio of 3.4 to 1, and a specific fuel consumption of 1.22 lbfuel/lbthrust per hour. The fuels used were Jet-A fuel and two synthetic kerosene fuels. Synthetic fuels are attractive in the aviation industry because of their potential for reducing energy dependence and the growing need for higher efficiencies, while reducing emissions. While synthetic fuels show multiple benefits for their use over traditional jet fuels, the sound and vibration signatures were less investigated and this brought the need of this paper. This is especially important if the sound shows a noticeable decibel difference of three decibels or more. The three decibels difference is key, since humans can perceive a difference in sound, based on the logarithmic scale for decibel, of three decibels or more. Hence, A-weighting would be used for the determination of a noticeable difference in sound. This study investigates the vibrations characteristics within the 1/3 octave band of 400 Hz. The sound and vibrations of the engine were measured with an advanced Bruel & Kjaer condenser microphone and piezoelectric tri-axial accelerometer. The sound and vibration characteristics in the mid frequency range is of particular interest regarding combustion of the gas turbine. It has been determined that a 7 dB(A) difference between the reference fuel and the synthetic fuel was achieved at 400 Hz on a 1/3 octave band analysis. Overall, sound signals coming from one of the synthetic kerosene fuels was higher than Jet-A. The highest fuel throughout the vibrations signals overall was Jet-A and at least one of the synthetic kerosene fuels. All data was processed using a Constant Percentage Bandwidth analysis. Understanding the combustion from the sound and vibrations point-of-view can help to foresee the potential danger to the components of the engine, understand the potential effects of sound on the human passenger, and work towards a design to mitigate these phenomena, if necessary.Copyright

Jet-A Combustion in an Indirect Injection Compression Engine Versus a Direct Injection Compression Engine at Same Load and Speed

This study compares combustion of Jet-A in an indirect injection (IDI) compression ignition engine and a direct injection (DI) compression ignition engine at the same load and speed. The Jet-A was blended (75Jet-A): 75% Jet-A and 25% Ultra Low Sulfur Diesel # 2 (ULSD) by mass. Both engines had a load of 4.5 bars Indicated Mean Effective Pressure (IMEP) and were run at 2000 RPM.The IDI engine configuration was very similar to that used in High Mobility Multipurpose Wheeled Vehicles (HMMWV).The research showed that combustion pressure in the IDI engine separate combustion chamber was 81 bars versus 71 bars in the main combustion chamber showing high gas-dynamics losses at transfer passages while in the DI engine the peak pressure reached 65 bars.The Apparent Heat Release Rate (AHRR) in the IDI engine has both the premixed and diffusion stage combined while in the DI classical combustion there are visible both the premixed and diffusion burn stages. The results show that in both engines there is a Low Temperature Heat Release (LTHR) region before top dead center (BTDC). The mass averaged instantaneous temperature reached 1750 K in the direct injection engine being the same for both fuels and for the IDI engines reached 1700 K in main combustion chamber and 1950 K in the separate combustion chamber for both fuels.The study showed that there are significant differences in the shape of the AHRR between the engines, nevertheless, the Jet-A has very similar combustion characteristics with ULSD in both combustion systems making a viable option as a substitute fuel to use in High Mobility Multipurpose Wheeled Vehicles (HMMWV).Copyright