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Reduced emissions, improved fuel economy, and improved performance are a priority for manufacturers of internal combustion engines. However, these three goals are normally interrelated and difficult to optimize simultaneously. Studying the experimental heat release provides a useful tool for combustion optimization. Heavy-duty diesel engines are inherently transient, even during steady state operation engine controls can vary due to exhaust gas recirculation (EGR) or aftertreatment requirements. This paper examines the heat release and the derived combustion characteristics during steady state and transient operation for a 1992 DDC series 60 engine and a 2004 Cummins ISM 370 engine. In-cylinder pressure was collected during repeat steady state SET and the heavy-duty transient FTP test cycles.

The range-extended electric vehicle (REEV) is a complex nonlinear system powered by internal combustion engine and electricity stored in battery. This research proposed a Multiple Operation Points (MOP) control strategy of REVV based on operation features of REEV and the universal characteristic curve of the engine. The switching logic rules of MOP strategy are designed for the desired transition of the operation mode, which makes the engine running at high efficiency region. A Genetic algorithm (GA) is adapted to search the optimal solution. The fuel consumption is defined as the target cost function. The demand power of engine is defined as optimal variable. The state of charge (SOC) and vehicle speed are selected as the state variables. The dynamic performance of vehicle and cycling life of battery is set as the constraints. The optimal switching parameters are obtained based on this control strategy. Finally, a dynamic simulation model of REEV is developed in Matlab/Simulink.

Reactivity controlled compression ignition (RCCI) is a form of dual-fuel combustion that exploits the reactivity difference between two fuels to control combustion phasing. This combustion approach limits the formation of oxides of nitrogen (NOX) and soot while retaining high thermal efficiency. The research presented herein was performed to determine the influences that high reactivity (diesel) fuel properties have on RCCI combustion characteristics, exhaust emissions, fuel efficiency, and the operable load range. A 4-cylinder, 1.9 liter, light-duty compression-ignition (CI) engine was converted to run on diesel fuel (high reactivity fuel) and compressed natural gas (CNG) (low reactivity fuel). The engine was operated at 2100 revolutions per minute (RPM), and at two different loads, 3.6 bar brake mean effective pressure (BMEP) and 6 bar BMEP.

The Quarter Wave Coaxial Cavity Resonator (QWCCR) plasma igniter is designed, from previous theoretical work, as an ignition source for an internal combustion engine. The present research has explored the implementation of the QWCCR into an internal combustion (IC) engine. The QWCCR design parameters of inner conductor length, loop geometry, and loop position were varied for two igniters of differing operating frequency. Variations of the QWCCR radio frequency (RF) parameters, as a function of engine geometry, were studied by placing the igniter in a combustion chamber and manually varying the crank position. Three identical igniters were fitted with dielectric inserts and the parameters were studied before and after ignition was sustained in a twin-cylinder engine. Optimal resonator geometries were determined. Radio frequency parameter invariance was found with respect to crank angle and piston distance. The first successful IC engine ignition using a QWCCR was achieved.

The free piston engine combined with a linear electric alternator has the potential to be a highly efficient converter from fossil fuel energy to electrical power. With only a single major moving part (the translating rod), mechanical friction is reduced compared to conventional crankshaft technology. Instead of crankshaft linkages, the motion of the translator is driven by the force balance between the engine cylinder, alternator, damping losses, and springs. Focusing primarily on mechanical springs, this paper explores the use of springs to increase engine speed and reduce cyclic variability. A numeric model has been constructed in MATLAB®/Simulink to represent the various subsystems, including the engine, alternator, and springs. Within the simulation is a controller that forces the engine to operate at a constant compression ratio by affecting the alternator load.

Linear engine alternator (LEA) design optimization traditionally has been difficult because each independent variable alters the motion with respect to time, and therefore alters the engine and alternator response to other governing variables. An analogy is drawn to a conventional engine with a very light flywheel, where the rotational speed effectively is not constant. However, when springs are used in conjunction with an LEA, the motion becomes more consistent and more sinusoidal with increasing spring stiffness. This avoids some attractive features, such as variable compression ratio HCCI operation, but aids in reducing cycle-to-cycle variation for conventional combustion modes. To understand the cycle-to-cycle variations, we have developed a comprehensive model of an LEA with a 1kW target power in MATLAB®/Simulink, and an LEA corresponding to that model has been operated in the laboratory.

The basic design of a purely rotary motion engine has potentially many advantages over the conventional piston-crank internal combustion engine. Although only one rotary engine has been successfully placed into production, rotary mechanisms still show promise in the market place. A comprehensive review of rotary engine concepts is presented with an emphasis placed on the last 30 years. Suggestions are made as to where research concentrations should be placed to improve the progress of a rotary engine.

Recent free piston engine research reported in the literature has included development efforts for single and dual cylinder devices through both simulation and prototype operation. A single cylinder, spring opposed, oscillating linear engine and alternator (OLEA) is a suitable architecture for application as a steady state generator. Such a device could be tuned and optimized for peak efficiency and nominal power at unthrottled operation. One of the significant challenges facing researchers is startup of the engine. It could be achieved by operating the alternator in a motoring mode according to the natural system resonant frequency, effectively bouncing the translator between the spring and cylinder, increasing stroke until sufficient compression is reached to allow introduction of fuel and initiation of combustion. To study the natural resonance of the OLEA, a numeric model has been built to simulate multiple cycles of operation.

This paper examines the energy pathways of a 29cc air-cooled two-stroke engine operating on natural gas with different exhaust geometries. The engine was operated at wide-open-throttle at a constant speed of 5400 RPM with ignition adjusted to yield maximum brake torque while the fueling was adjusted to examine both rich and lean combustion. The exhaust configurations examined included an off-the-shelf (OTS) model and two other custom models designed on Helmholtz resonance theory. The custom designs included both single and multi-cone features. Out of the three exhaust systems tested, the model with maximum trapping efficiency showed a higher overall efficiency due to lower fuel short-circuiting and heat transfer. The heat transfer rate was shown to be 10% lower on the new designs relative to OTS model.

Performance of a natural gas two-stroke engine incorporated in a 1-kW free-piston oscillating Linear Engine Alternator (LEA) - a household electricity generator - was investigated under different resonant frequencies for pre-design phase purposes. To increase the robustness, power density, and thermal efficiencies, the crank mechanism in free-piston LEA is omitted and all moving parts of the generator operate at a fixed resonant frequency. Flexure springs are the main source of the LEA’s stiffness and the mass-spring dynamics dominates the engine’s speed. The trade-off between the engine’s performance, mass-spring system limits, and power and efficiency targets versus the LEA speed is very crucial and demands a careful investigation specifically at the concept design stages to find the optimum design parameters and operating conditions. CFD modeling was performed to analyze the effects of resonant frequency on the engine’s gas exchange behavior.

With few exceptions most internal combustion engines use a slider-crank mechanism to convert reciprocating piston motion into a usable rotational output. One such exception is the Stiller-Smith Mechanism which utilizes a kinematic inversion of a Scotch yoke called an elliptic trammel. The device uses rigid connecting rods and a floating/eccentric gear train for motion conversion and force transmission. The mechanism exhibits advantages over the slider-crank for application in internal combustion engines in areas such as balancing, size, thermal efficiency, and low heat rejection. An overview of potential advantages of an engine utilizing the Stiller-Smith Mechanism is presented.

Series hybrid electric vehicles (HEVs) require power-plants that can generate electrical energy without specifically requiring rotary input shaft motion. A small-bore working prototype of a two-stroke spark ignited linear engine-alternator combination has been designed, constructed and tested and has been found to produce as much as 316W of electrical energy. This engine consists of two opposed pistons (of 36 mm diameter) linked by a connecting rod with a permanent magnet alternator arranged on the reciprocating shaft. This paper presents the numerical modeling of the operation of the linear engine. The piston motion of the linear engine is not mechanically defined: it rather results from the balance of the in-cylinder pressures, inertia, friction, and the load applied to the shaft by the alternator, along with history effects from the previous cycle. The engine computational model combines dynamic and thermodynamic analyses.

With the purpose of reducing emission level while maintaining the high torque character of diesel engine, various solutions have been proposed by researchers over the world. One of the most attractive methods is to use dual fuel technique with premixed gaseous fuel ignited by a relatively small amount of diesel. In this study, Methane (CH4), which is the main component of natural gas, was premixed with intake air and used as the main fuel, and diesel fuel was used as ignition source to initiate the combustion. By varying the proportion of diesel and CH4, the combustion and emissions characteristics of the dual fuel (diesel/CH4) combustion system were investigated. Different cases of CFD studies with various concentration of CH4 were carried out. A validated 3D quarter chamber model of a single cylinder engine (diesel fuel only) generated by using AVL Fire ESE was modified into dual fuel mode in this study.

Due to tightening emission legislations, both within the US and Europe, including concerns regarding greenhouse gases, next-generation combustion strategies for internal combustion diesel engines that simultaneously reduce exhaust emissions while improving thermal efficiency have drawn increasing attention during recent years. In-cylinder combustion temperature plays a critical role in the formation of pollutants as well as in thermal efficiency of the propulsion system. One way to minimize both soot and NOx emissions is to limit the in-cylinder temperature during the combustion process by means of high levels of dilution via exhaust gas recirculation (EGR) combined with flexible fuel injection strategies. However, fuel chemistry plays a significant role in the ignition delay; hence, influencing the overall combustion characteristics and the resulting emissions.

A conceptual understanding of modularity in internal combustion engines (defined as design, operation, and sensing on an individual cylinder basis) is presented. Three fundamental modular concepts are identified. These are dissimilar component sizing and operation, component deactivation, and direct sensing. The implementation of these concepts in spark ignition internal combustion engines is presented. Several modular approaches are reviewed with respect to breathing, fueling, power generation, and sensing. These include dissimilar orientation, geometry, and activation of multiple induction runners, partial or total disablement of valves through direct or indirect means, dissimilar fueling of individual cylinders, skipping the combustion event of one or more cylinders, deactivation of dissimilar individual cylinders or a group of cylinders, and individual cylinder gas pressure and mixture strength sensing.

Evermore demanding market and legislative pressures require stationary lean burn natural gas engines to operate at higher efficiencies and reduced levels of emissions. Higher in-cylinder pressures and leaner air/fuel ratios are required in order to meet these demands. The performance and durability of spark plug ignition systems suffer as a result of the increase in spark energy required to maintain suitable engine operation under these conditions. Advancing the state of the art of ignition systems for these engines is critical to meeting increased performance requirements. Laser-spark ignition has shown potential to improve engine performance and ignition system durability to levels required meet or exceed projected requirements. This paper discusses testing which extends previous efforts [1] to include constant fueling knock, misfire, thermal efficiency, and NOx emissions mapping of a single cylinder lean burn natural gas engine.

The key to overcoming Low Temperature Combustion (LTC) load range limitations is based on suitable control over the thermo-chemical properties of the in-cylinder charge. The proposed alternative to achieve the required control of LTC is the use of two separate fuel streams to regulate timing and heat release at specific operational points, where the secondary fuel, with different autoignition characteristics, is a reformed product of the primary fuel in the tank. It is proposed in this paper that the secondary fuel is produced using Thermo-Chemical Recuperation (TCR) with steam/fuel reforming. The steam/fuel mixture is heated by sensible heat from the engine exhaust gases in the recuperative reformer, where the original hydrocarbon reacts with water to form a hydrogen rich gas mixture. An equilibrium model developed by Gas Technology Institute (GTI) for n-heptane steam reforming was applied to estimate reformed fuel composition at different reforming temperatures.

As the demand for higher engine efficiencies and lower emissions drive stationary, spark-ignited reciprocating engine combustion to leaner air/fuel operating conditions and higher in-cylinder pressures, increased spark energy is required for maintain stable combustion and low emissions. Unfortunately, increased spark energy negatively impacts spark plug durability and its effectiveness in transmitting adequate energy as an ignition source. Laser ignition offers the potential to improve ignition system durability, reduce maintenance, as well as to improve engine combustion performance. This paper discusses recent engine combustion testing with an open beam path laser ignition system in a single-cylinder engine fueled by natural gas. In particular, engine knock and misfire maps are developed for both conventional spark plug and laser spark ignition. The misfire limit is shown to be significantly extended for laser ignition while the knock limit remains virtually unaffected.

Two and three-dimensional test cases were simulated using a detailed kinetic mechanism for di-methyl ether to represent methane combustion. A piston-bowl assembly for the compression and expansion strokes with combustion has been simulated at 1500 RPM. A fine grid was used for the 2-D simulations and a rather coarse grid was used for the 3-D calculations together with a k-ε subgrid-scale turbulence model and a partially stirred reactor model with three time scales. Ignition was simulated artificially by increasing the temperature at one point inside the cylinder. The results of these simulations were compared with experimental results. The simulation involved an engine with a homogeneous charge of methane as fuel. Results indicate that pressure fluctuations were captured some time after the ignition started, which indicates knock conditions.

The KIVA family of codes (Amsden et al., 1989,1993,1997) are being used by many researchers for internal combustion engine simulation. For these codes to continue to be useful, improvements need to be made to make them more efficient. One of the most CPU intensive parts of these codes is the pressure solver. Improvement in the convergence of the pressure solver could have a significant effect on the performance of the overall code. This paper presents the theory behind the matrix solution procedure utilized by KIVA. A different approach to preconditioning is then presented. When implemented, it is shown that the overall CPU time required to perform a simulation is reduced by up to 20% for pressure dominated three-dimensional simulations. This is accomplished without an increase in memory allocation.