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We have proposed the engine featuring a new compressive combustion principle based on pulsed supermulti-jets colliding through a focusing process in which the jets are injected from the chamber walls to the chamber center. This principle has the potential for achieving relatively silent high compression around the chamber center because autoignition occurs far from the chamber walls and also for stabilizing ignition due to this plug-less approach without heat loss on mechanical plugs including compulsory plasma ignition systems. Then, burned high temperature gas is encased by nearly complete air insulation, because the compressive flow shrinking in focusing process gets over expansion flow generated by combustion.

Computation of the three-dimensional flow in the intake ports and the cylinders of real engines, including moving valves and piston, has been carried out by solving the Navier-Stokes equations. No explicit turbulence models are used. An extended version of the SIMPLE and ICE method is employed to simulate density variations in engines, which are connected with compression rate, heat transfer, and compressibility. A third-order upwind scheme is combined with this method. Computational results show complex flow fields such as separated flows near the valve seat and small vortices of the order of the mesh size near the end of compression. These computational results are compared with the LDV measurements.

Turbulent flows in a model engine having a square piston were analyzed in detail by using a numerical simulation method with higher-order accuracy to perform simulations on an orthogonal homogeneous grid without grid motions. Calculations were performed during several continuous engine cycles. A better understanding of the cycle-by-cycle differences, i.e., cyclic variations, in flow fields may lead to more effective ways of stabilizing combustion.

Large Eddy Simulation of the turbulent premixed-flame in engine is performed in a wide range of the operating conditions such as engine speed, air-fuel ratio, and ignition timing. Firstly, a mathematical formulation suitable for Large Eddy Simulation (LES) and Direct Numerical Simulation (DNS) of the compressible turbulence and combusting flows is derived, which is the Multi-Level formulation. And a numerical algorithm based on the formulation is developed in order to calculate precisely the supergrid fluctuations of the physical quantities. As the determinations of the subgrid-turbulence and flame wrinkling, the Yakhot-Orszag turbulence model based on the Renormalization Group theory(RNG theory) and a flame-sheet model are combined with the numerical code. Computations are performed for a real engine with dual intakeport and valves. Obtained computational data agrees well with the experimental data on turbulence-intensity and pressure history.

Computational and theoretical analyses for a new type of engine (Fugine), which was proposed by us based on the colliding of pulsed supermulti-jets, indicate a potential for very high thermal efficiencies and also less combustion noise. Three types of prototype engines were developed. One of them has a low-cost gasoline injector installed in the suction port and a double piston system in which eight octagonal supermulti-jets are injected and collide. Combustion experiments conducted on the prototype gasoline engine show high thermal efficiency comparable to that of diesel engines and less combustion noise comparable to that of traditional spark-ignition gasoline engines. This paper presents some combustion experiments of one of the other piston-less prototype engines having bi-octagonal pulsed multi-jets injected from fourteen nozzles.

A single-point autoignition gasoline engine (Fugine) proposed by us previously has a strongly asymmetric double piston unit without poppet valves, in which pulsed multi-jets injected from eight suction nozzles collide around the combustion chamber center. Combustion experiments conducted on this engine at a low operating speed of 2000 rpm using gasoline as the test fuel under lean burn conditions showed both high thermal efficiency comparable to that of diesel engines and silent combustion comparable to that of conventional spark-ignition gasoline engines. This gasoline engine was tested with a weak level of point compression generated by negative pressure of about 0.04 MPa and also at an additional mechanical homogeneous compression ratio of about 8:1 without throttle valves. After single-point autoignition, turbulent flame propagation may occur at the later stage of heat release.

In recent years, a new type of engine (Fugine) based on the colliding of pulsed supermulti-jets was proposed by us, which indicates the potential for attaining very high thermal efficiencies and also less combustion noise. A prototype engine with eight nozzles for injecting octagonal pulsed supermulti-jets, which was developed with a low-cost gasoline injector and a double piston system, showed high thermal efficiency comparable to that of diesel engines and also less combustion noise comparable to that of traditional spark-ignition gasoline engines. Another type of prototype piston-less engine having fourteen bioctagonal nozzles was also developed and test results confirmed the occurrence of combustion, albeit it was unstable. In this work, time histories of pressure were measured in the combustion chamber of the piston-less prototype engine under a cold flow condition without combustion in order to examine the compression level obtained with the colliding supermulti-jets.

A new engine concept (Fugine) based on colliding pulsed supermulti-jets was proposed in recent years, which is expected to provide high thermal efficiencies over 50% and less combustion noise. Theoretical analyses indicate a high potential for thermal efficiency over 60%. Three types of prototype engines have been developed. The first prototype engine based only on the colliding of pulsed supermulti-jets with fourteen nozzles has no piston compression, while the second type equipped with a low-cost gasoline injector in the suction port has a double piston system and eight jet nozzles. Combustion experiments conducted on the second prototype gasoline engine show high thermal efficiency similar to that of traditional diesel engines and lower combustion noise comparable to that of traditional spark-ignition gasoline engines.

In our previous papers, a new concept of a compressive combustion engine (Fugine) was proposed based on the collision of pulsed supermulti-jets, which can enclose the burned gas around the chamber center leading to an air-insulation effect and also a lower exhaust gas temperature due to high single-point compression. In order to examine the compression level and air-insulation effect as basic data for application to automobiles, aircraft, and rockets, a prototype engine based on the concept, i.e., a piston-less prototype engine with collision of bi-octagonal pulsed multi-jets from fourteen nozzles, was developed. Some combustion results [Naitoh et al. SAE paper, 2016] were recently reported. However, there was only one measurement of wall temperature and pressure in the previous report. Thus, in this paper, more experimental data for pressures and temperatures on chamber walls and exhaust temperatures, are presented for the prototype engine.

A single lightweight engine capable of operating over a wide range of Mach numbers from startup to the hypersonic regime is proposed for automobiles and airplanes. Traditional piston engines, turbojet engines, and scram jet engines operate only under a narrower range of conditions. A compression system of colliding super multijets is proposed instead of a traditional turbofan. This ultimate engine system can be extended with a special piston system to achieve an improved fuel consumption rate, while maintaining a low noise level.

For various densities of gas jets including very light hydrogen and relatively heavy ones, the penetration length and diffusion process of a single high-speed gas fuel jet injected into air are computed by performing a large eddy simulation (LES) with fewer arbitrary constants applied for the unsteady three-dimensional compressible Navier-Stokes equation. In contrast, traditional ensemble models such as the Reynolds-averaged Navier-Stokes (RANS) equation have several arbitrary constants for fitting purposes. The cubic-interpolated pseudo-particle (CIP) method is employed for discretizing the nonlinear terms. Computations of single-component nitrogen and hydrogen jets were done under initial conditions of a fuel tank pressure of gas fuel = 10 MPa and back pressure of air = 3.5 MPa, i.e., the pressure level inside the combustion chamber after piston compression in the engine.

Fluid-dynamic principle for obtaining relatively stable combustion is found by performing cycle-resolved computations of turbulent flows in engines. Cycle-resolved computations are performed by using the implicit large eddy simulation (ILES) code, which we have proposed earlier. Calculations over continuous cycles show us the existence of “silent domain” in the engine cylinder, having weak cyclic-variations of flow. Time-dependent velocities averaged over six cycles, mean velocities, are also small in the silent domain. Moreover, we examine further on why cyclic variations of flow is weaker in the silent domain. This brings us a way for controlling cyclic variations for several engines.

Instability of the Initial flame propagation is examined after computing the flows during three continuous cycles of an engine. Cycle-resolved large eddy simulation (CLES) is employed for these computations. First, we calculated the compressible turbulent flows during three continuous cycles in a model engine having square piston. Then, the initial flame propagation processes are calculated by using G-equation at the flow condition of TDC. Grid system of 1,000,000 points is employed. Relation between cyclic-resolved turbulence and initial flame is qualitatively examined by the computational results.

Much effort has been devoted to studies on auto-ignition engines of gasoline including homogeneous-charge combustion ignition engines over 30 years, which will lead to lower exhaust energy loss due to high-compression ratio and less dissipation loss due to throttle-less device. However, the big problem underlying gasoline auto-ignition is knocking phenomenon leading to strong noise and vibration. In order to overcome this problem, we propose the principle of colliding pulsed supermulti-jets. In a prototype engine developed by us, octagonal pulsed supermulti-jets collide and compress the air around the center point of combustion chamber, which leads to a hot spot area far from chamber walls. After generating the hot spot area, the mechanical compression of an asymmetric double piston unit is added in four-stroke operation, which brings auto-ignition of gasoline.

An inexpensive, lightweight, and relatively quiet engine reactor that has the potential to achieve thermal efficiency over 50% for small engines was proposed in our previous reports, which is achieved with colliding supermulti-jets that create air insulation to encase burned gas around the chamber center, avoiding contact with the chamber walls and piston surfaces. The colliding of pulse jets can maintain high pressure ratio for various air-fuel ratios, whereas traditional homogeneous compression engines due to piston cannot get high pressure ratio at stoichiometric condition. Emphasis is also placed on the fact that higher compression in this engine results in less combustion noise because of encasing effect. Here, a small prototype engine having supermulti-jets colliding with pulse and strongly-asymmetric double-piston system is examined by using computational experiments. Pulse can be generated by the double piston system of a short stroke of about 40mm.

In our previous reports based on computations and fluid dynamic theory, we proposed a new compressive combustion principle for an inexpensive and relatively quiet engine reactor that has the potential to achieve thermal efficiency over 50% even for small combustion chambers having less than 100 cc. This can be achieved with colliding supermulti-jets that create complete air insulation to encase burned gas around the chamber center. We originally developed two small prototype engine systems for gasoline. First one with one rotary valve for pulsating intake flow and sixteen nozzles of jets colliding has no pistons. Next, we developed the second one having a strongly-asymmetric double piston system with the supermulti-jets colliding, although there are no poppet valves. The second prototype engine can vary point-compression strength due to the supermulti-jets and homogeneous compression level due to piston, by changing phase and size of two gears.

We proposed a new compressive combustion principle for an inexpensive and relatively quiet engine reactor that has the potential to achieve incredible thermal efficiency. The high efficiency can be achieved with colliding supermulti-jets that create complete air insulation to encase burned gas around the chamber center. We developed a small prototype engine system for gasoline, which has a strongly-asymmetric double piston and the supermulti-jets colliding with pulse. In this report, we will show combustion experimental results at startup and at steady state operation. We obtained exhaust temperature over 100 degree Celsius and pressure data, which imply auto-ignition occurrence of gasoline.

The authors have previously proposed a plume ignition and combustion concept (i.e., PCC combustion), in which a hydrogen fuel is directly injected to the combustion chamber in the latter half of compression stroke and forms a richer mixture plume. By combusting the plume, both cooling losses and NOx formation are reduced. In this study, thermal efficiency was substantially improved and NOx formation was reduced with PCC combustion by optimizing such characteristics as direction and diameter of the jets in combination with combustion of lean mixture. Output power declined due to the lean mixture, however, was recovered by supercharging while keeping NOx emissions at the same level. Thermal efficiency was further improved by slightly re-optimizing the jet conditions.

A new engine concept based on pulsed supermulti-jets colliding at a small area around the chamber center was proposed in our previous research. It was expected to provide noiseless high compression ratio and nearly-complete air-insulation on chamber walls, leading to high thermal efficiency. In the previous reports, three-dimensional computations for the unsteady compressible Navier-Stokes equation were conducted, which were qualitative because of using regular grid method. This time, we develop a new numerical code in order to quantitatively simulate the compression level caused by the jets colliding with pulse. It is achieved by applying a staggered grid method to improve conservatibity of physical quantities at very high compression in combustion phenomena. Computations at a simple condition were fairly agreed with a theoretical value. Computational results obtained for a complex geometry of an engine by the new code had less error than one with previous codes.

In our previous reports based on computational experiments and fluid dynamic theory, we proposed a new compressive combustion principle for an inexpensive, lightweight, and relatively quiet engine reactor that has the potential to achieve incredible thermal efficiency over 60% even for small combustion chambers having less than 100 cc. This level of efficiency can be achieved with colliding supermulti-jets that create complete air insulation to encase burned gas around the chamber center, thereby avoiding contact with the chamber walls, including the piston. We originally developed an actual prototype engine system for gasoline. The engine has a strongly-asymmetric double piston and the supermulti-jets colliding with pulse, although there are no poppet valves. The number of jets pulsed for intake and exhaust is eight, while both of bore and stroke are about 40mm.