Search

Small, turbine-powered eAPUs (electric Auxiliary Power Unit) have poor off-design performance and efficiency. Turbo eAPUs remain competitive where efficiency is sacrificed to lightness and compactness. The first part of this paper summarizes the transformation of a very efficient, very large automotive turbocharger into an eAPU. A satisfactory solution for the design of the heavy fuel combustor has been found on the Giandomenico’s site. The performance of the APU is evaluated at the Garrett nominal air conditions (T0=302.6 K, p0=0.962 bar, dry air). The turbogas has an approximately linear braking torque from 50% to 100% load at nearly maximum efficiency. Below 50% load, it is more convenient to vary the maximum temperature of the cycle and adjust the generator torque. However, a better compromise can be obtained by coupling the APU with a battery that would supply the electric power under 50% load. The use of a recuperator is not convenient due to the increase in volume and the additional complication. The problem of the intake air filtering is particularly serious in dirty/sandy ground applications. Regarding efficiency, the turbogas is no match for the diesel eAPUs.

The 2014 Formula 1 season was characterized by the return of supercharging through turbocharger in a complex hybrid propulsion system. The new direct-injection turbocompound engines V6 of 1600cc have innovative systems for the recovery of the energy otherwise wasted (Energy Recovery System - ERS). The following article introduces a one-dimensional simulation of two different engine concepts. The first one is the “split turbocharger” arrangement that allows the design of a very short “log” exhaust; the other with a traditional short-shaft turbocharger that needs a more complex and longer “tubular” exhaust. The paper demonstrates that the longer “tubular” exhaust dissipates more energy that the shorter “log” one. In this way, the efficiency is impaired and the “log” exhaust makes it possible to have more energy available to the wheels with the same amount of fuel and with the same limitation on the fuel flow. Therefore, with the current limitations in the fuel, the “log” exhaust / split-turbo arrangement is more convenient for current Formula 1 engines. In this paper, loads, pressures, power and speed of the various components of the turbocompound engine were simulated. A standard turbocharger compressor and turbine were used for the log and tubular exhaust arrangement and the results were compared. Even if the turbocharger matching is not optimal, in fact the boost pressure does not reach the maximum allowed, the comparison between the two arrangements is still valid.

A feasibility study for the installation of a CRDID (Common Rail Direct Injection Diesel) on a light helicopter is introduced. The total mass available for the CRDID is evaluated starting from fuel consumption and helicopter data. The conversion of an automotive unit was discarded to excessive mass and excessive costs of the conversion. A derivative of an automotive engine was then considered. This solution proved to be feasible. The installation of the new CRDID was then studied. The turbocharger and the cooling system were defined for the application. The result was the evaluation of the power plant installation mass that proved to be much lower than the maximum admissible. The installation is then possible. La Se presenta un estudio de factibilidad para la instalación de un CRDID ( Common Rail Direct Injection Diesel por sus siglas en ingles) en un helicóptero ligero . La masa total disponible para el CRDID se calcula a partir de los datos de consumo de combustible y datos de helicópteros. La conversión de una unidad de automoción se descartó debido a los costos excesivos en masa, y costos excesivos en conversión. A continuación se considera un derivado de un motor de automóvil . Esta solución ha demostrado ser factible. Posteriormente, se estudió la instalación de la nueva CRDID . El sistema de refrigeración y el turbocompresor se definieron para la aplicación. El resultado fue el calculo de la masa de instalación de la planta de energía que resultó ser mucho menor que el máximo admisible. La instalación es entonces realizable.

The primary task in DI (Direct Injection) diesel engines design is the fulfilment of the required emission limits. This result should be achieved with acceptable power-to-rpm diagrams, acceptable fuel consumption, acceptable power density and affordable purchase and maintenance expenses. The most common approach to fulfil these requirements is the downsizing. In this case a significant increase in the crankshaft speed and boost pressure is unavoidable. In this way, an improvement in airflow through the redesign of the intake and exhaust geometry is obtained. Unfortunately, duct design is extremely difficult due to “Mach lock”. A further important boundary condition is due the injector inertia. The dynamic response improves with small injectors due to the Newton’s second law. Small injectors designed for unitary power of 15 to 70 HP are extremely common. Therefore, most of the research is centered on these injectors. Furthermore, their small inertia favors better opening and closing time. Nozzles number and position is also greatly influential on combustion performance. The larger surface of the spray reduces the gasification time of the droplets. For these reasons, multiple injectors systems may be used in large high pressure HSDI-CR (High Speed Direct Injection – Common Rail) diesels. Multi injection was commonplace in relatively large old diesels. This paper proposes new intake duct geometries for modern two-injectors-per-cylinder truck-size engines. For this purpose a new promising, patented concept is introduced. The study includes flow simulations during the intake phase. This patented geometry induces the presence of two extremely strong swirls approximately centered to the injectors, with excellent swirl coefficient and high flow rate. The use of swirl generators on the manifolds avoids the necessity to design helical intake ducts. This patented approach simplifies head design. Moreover, using a VG (Variable Geometry) arrangement for the volutes (swirl generators) it is possible to tune the swirl index at the optimum for every crankshaft velocity and every load. In this way, the vehicle fuel consumption is also reduced.

This paper introduces a Montecarlo Genetic Algorithm, hierarchical, multi-objective optimization of a Vertical Take Off landing Unmanned Aerial Vehicle having a tail sitter configuration. An optimization of the hierarchical type is introduced in place of the methods generally used multi-objective optimization, such as Pareto and “arbitrary” weighted sums. A Montecarlo method optimizes the weights of the final objective function used by the Genetic Algorithm. A very simple “spreadsheet based” algorithm defines the CAD model of the Genetic Algorithm individuals in order to evaluate the performance of the candidates. The optimization method described in this study appears to be very effective. Then experimental tests were conducted with scaled-down prototypes. Four flight tests were performed: Take Off, Cruise, Slow flight, Landing. A Taguchi matrix was defined for each experiment. The tests started from a prototype that comes directly from the Montecarlo Genetic Algorithm optimization and led to the final prototype shown along the paper (page 7, right figure). Unfortunately, the tail sitter approach proved poor control authority in the final phase of the vertical landing. Even the “final” prototype showed unsatisfactory behavior in case of erratic wind gusts. This unsolved problem is common to the tail sitter configuration that requires a power control by air jets or additional propeller to control the aircraft in the final phase of landing. Unfortunately, this necessity renders the tail sitter configuration inconvenient for small Unmanned Aerial Vehicles.

This paper introduces a method to efficiently monitor the status of a piston engine during flight. ECUs (Electronic Control Units) make it possible to fly safely without emergencies or urgencies with random electronic failures of components and connections. The same can be easily done on older engines by adding a reliable digital monitoring system and an automated calibration of the carburetors. In fact, their reliability is several order of magnitude inferior to modern turboshafts. In modern engines with FADEC (Full Authority Digital Electronic Control) as the “on” button is pressed the sensors and actuators are checked. The CPUs will then run start-up during the cranking phase (engine running without ignition). If everything is all right, then the engine starts and the post start checks are also performed. During flight, the ECU checks CPUs, sensors and actuators. Therefore, the electronic system can be monitored with high reliability without much effort. The sensors may crosscheck the engine situation and may output very reliable early diagnosis of incoming failures. Statistical data on spare parts are invaluable for monitoring application, signaling weak or not-lasting components and failure modes. This is another advantage of automotive piston engines conversions to aircraft use.

Multiple-speed gearboxes with computer controlled automatic gear selection devices are a common possible choice in cars. Robotized gear insertion of one tenth of a second is possible. Economical and weight consideration are to be made to verify if it is convenient to use a smaller engine and a larger gearbox with a wider choice of speeds. In this paper, an automotive application for a public transport vehicle based on a Class S chassis with the choice of common-rail direct injection engines. This choice is particular unfavorable for the multispeed gearbox since common-rail engines have very flat specific fuel consumption curves. The lumped mass model implemented is conceived to estimate velocity, acceleration and fuel consumption starting from aerodynamic, inertia and thermodynamic data of the vehicle. The estimated data of performance and fuel consumption were compared with measured values. A Genetic elitarian Algorithm (GA) was used to optimise the engine choice and the gearbox speeds distribution. A maximum reduction of 15% was then calculated with a 16-speeds gearbox and a 140 HP/300Nm engine in comparison with the standard 5-speeds 204 HP/500Nm engine. This fuel reduction was obtained on the mixed city-motorway cycle. In this case, maximum speed is limited to 180km/h and the 0-100km/h acceleration is reduced to 11s (from the original 8.6s). The weight remains almost unaltered since the 204 HP engine is heavier than the 140 HP and this largely compensates the gearbox weight increase. The multiple speed solution seems to be very interesting also for public transports vehicles and for trucks. © 2015 Pushpa Publishing House, Allahabad, India.

Electric turbocompounding in racing spark ignition engine is focused on transient operation. Classical compressor and turbine maps should be adapted for this particular condition. Electric turbocompounding has limited torque and power available on the electric side. For this reason, an ad hoc solution should be devised. A low inertia solution is proposed in this paper with the advantage of minor modifications on existing commercial highly optimized turbochargers. A large advantage over the current solution may be achieved. In this solution, a very low inertia electric/motor generator is magnetically coupled to the turbocharger on the compressor side of the shaft. The electromagnetic coupling acts also as a torque limiter allowing extremely large slips between turbocharger and generator shafts.

Starting from a good automotive engine is always a good idea, also for brand new automotive design. In the case of automotive to aircraft conversions, the automotive engine is modified as little as possible. This approach has several advantages: reduced development time, good reliability and availability of cheap and worldwide spare parts. What it may appear a good idea is to tune up the original ECU (electronic control unit) by using one of the several softwares available on the market. However, this approach is not feasible even for ultra light aircrafts. This is due to the lack of control on the software of these ECUs. In fact, automotive software timing or ECU set-up is performed in the following way. The final ECU manufacturer (who holds the responsibility of the hardware and the software in the final car ECU) supplies to the car manufacturer a “development ECU” with a “development Software”. This system is tuned on the engine and on the car to fulfill the car manufacturer requirement. When the tuning is considered satisfactory, the “maps” (the data inputted by the manufactured) are given to the ECU manufacturer. This later translates the data into the software of a “production ECU”, that is given back to the car manufacturer for final validation prior to serial production of ECU and car. In this case, even the car manufacturer does not have a full control of what happens inside his ECU. This is logical since the full responsibility is given to the ECU part supplier. So the tuning of a serial production ECU is more than a true programming. Results are unpredictable to a certain extent that depends on the level of knowledge of the person who performed the tuning and of the software house that implemented the software. The software that truly runs on serial production ECU is a well kept secret of the ECU manufacturer, since it is the knowledge of ECU. The simpler is the software the less expensive will be the ECU and the larger the profits of the ECU supplier. Tricks are hidden inside the ECU to obtain these results; these tricks multiplied per millions of ECU give the supplier a competitive advantage. So, even the car manufacturer has a limited control on what happens inside the real-time software of the ECU, what emerges is the engine and the car behavior. Aircraft conversions require the replacement of ECU, wirings and sensors with appropriate units. This assembly with its own software constitutes the aircraft FADEC.

Recent developments in diesel piston engine technology have increased performance in a very significant way. In this paper a new hybrid diesel-turbine engine is introduced and it is compared to up-to-date turboprops. The weak point of the common rail engine is the difficulty to obtain very fast injectors for large engines. Automotive injectors are available only for small power outputs. The problem was solved with a dual chambers piston with two injectors per cylinder. It is then possible to use off-the-shelf automotive common rail components even on very large diesel engines with benefits on combustion especially at medium low power level. The other more interesting advantage is a significant increase on crankshaft maximum speed and reduction of head mechanical stress. It is then possible to have smaller and more powerful turbodiesel and hybrid engines. Another advantage is the improved reliability of a dual injection system. The diesel – turbine hybrid power unit proposed in this paper combines the advantages of the turboprop/turbofan/turboshaft and piston turbo-diesel-prop / turbo-diesel-fan / turbodiesel engines. However, It should be clear than the automotive commercial common rail components should be treated to use jp4, jp8 and jet(A1) fuels and to fulfil aeronautical requirements.

A new generation of aircraft piston engines is currently being introduced on the market. These new engines come directly from the huge experience achieved in the motorcycle and automotive racing and production. However direct use of automotive power unit is not advisable, since car engines work mainly in the first quarter of the power output, while sport motorcycles are used in a very "light" way, with the engines that span several times through the entire range of power outputs and rpm. The other problem is fuel. Aircraft spark ignition engine for ultralight and light aircrafts may continue to use automotive gasoline, while diesel engines for light up to cargo aircraft should use jet(A1) and jp4. However, the large experience obtained from racing/high-performance motorcycles, racing/high-performance cars and common rail engines cannot be ignored. Thousand of hours and billion of Euros have been spent for this development and the results are interesting. This paper tries to calculate the future aircraft engine performance from the many experimental data already available on a certain type of combustion chamber or better from a well defined and experimented cylinder unit. On the other side the "lean-thinking" approach to aircraft engine design may be not applicable. The lean thinking approach tends to prefer the time-to-market to the optimization of the engine unit. With engines that will probably stay on the market for 30 years this approach is not convenient. An important optimization during the design phase is possible with modern CAD tools. Mass and cost reduction may easily reach the 30%. On the other side the "brain storming approach" is not applicable to the heavily-constrained aircraft-engine design, where it is common that inapplicable solutions and ideas seem to be the best during the initial phase even to experts. Our research team developed three different families of engines: the first family uses the cylinder unit of a well proven motorcycle engine, which comes directly from racing and was sold in tenth of thousands in the world market. These spark ignition engines have 4 up to 16 cylinders (Figg. 1, 2), with power from 150 HP to 800 HP. This type of engines have very brilliant power to weight ratios with not superlative fuel consumptions. They are conceived for ultralight aircrafts and helicopters, tilt rotor, tilt shaft and tilt motor power lift V/STOL aircrafts. The second cylinder unit comes directly from the 2 valves FIAT 1900 jtd, that is one of the best two valves turbocharged common rail diesel available on the market. These units span from 4 up to 16 cylinders with power outputs from 175 HP (Fig. 3) up to 1000 HP. They run with jp4, jp8 or jet (A1) and can be bolted directly to the original engine mount of existing light aircraft like Cessna 172/182/337 or can be used in new light aircrafts. The third one is an originally conceived twin combustion chamber diesel family with output power from 600 HP to 4000 HP (hybrid engine) originally conceived for the Hercules C130J, ATR42 or ATR72 aircrafts (Figg. 4, 5). Our hybrid engine is composed by two separate engines: the VD007 diesel and a turboshaft. Each engine moves a separate contra rotating propeller. In ordinary flight the turboshaft works as a turbocharger. In this case the rear propeller is nearly idle. During take off or emergency the turboshaft combustion chamber is activated and additional power is available. In this case pitch is given to the rear propeller that outputs additional useful thrust. All these engines use only the thermo-fluid-dynamics and a few parts of the original cylinder unit, since aircraft application need extended modifications and, in many cases, complete redesign. However on all these engines a large amount of experimental, road and reliability data are available. Their direct application in the aircraft field is a plain mistake, since automotive and motorcycle are very different, but it is not the case to discard all this data that are available for free. For this reason innovative simulation methods were used to obtain engine performance envelope, with the possibility to choose the most convenient off-design solution on a certain aircraft, depending on the use and on the requirements. It is also possible to obtain reliability data for the aircraft FADEC (Full Authority Digital Engine Control) that controls all these new units. It is important to underline that airborne FADECs should be completely different from ground borne FADECs since in the aircraft application recovery strategies are to be chosen by the well trained pilot, while in the automotive field recovery is usually applied automatically in order to preserve engine integrity. A new method for the determination of the engine performance envelope is introduced as an example on the turbo/hybrid diesel unit for the C130J; this engine is called VD007. This approach has been successfully applied on the small diesel jtd family and also to the spark ignition family. © 2008 by the American Institute of Aeronautics and Astronautics, Inc.