Maximizing the indicated thermal efficiency with minimal amount of emissions is one of the main challenges to overcome in the field of internal combustion engines. The main obstacle that hinders achieving this goal is the typically low thermodynamic efficiency which is the ratio of the positive produced work on the piston to the amount of heat released inside the cylinder. Many concepts and technologies were innovated to maximize the thermodynamic efficiency. One of the main guidelines that have been followed to achieve so, is the ideal Otto’s cycle that predicts that increasing the compression ratio and/or the specific heat ratio of the combustion reactants, will maximize the thermodynamic efficiency. This study combines both high compression ratios and a high specific heat ratio via two of the main approaches used to maximize the thermodynamic efficiency. First, is the HCCI combustion mode. HCCI is typically operated at fuel-lean conditions, allowing to operate at higher compression ratios without having intense knock (pressure waves, generated by undesired autoignition, that can damage the engine). Second, air was replaced by an…

In a previous study, it was shown that isobaric combustion cycle, achieved by multiple injection strategy, is more favorable than conventional diesel cycle for the double compression expansion engine (DCEE) concept. In spite of lower effective expansion ratio, the indicated efficiencies of isobaric cycles were approximately equal to those of a conventional diesel cycle. Isobaric cycles had lower heat transfer losses and higher exhaust losses which are advantageous for DCEE since additional exhaust energy can be converted into useful work in the expander. In this work, the performance of isobaric combustion cycles in terms of indicated efficiency, emissions, and energy flow distribution is compared to the conventional diesel cycle but at a relatively lower compression ratio. A standard 17-compression ratio piston is replaced by a low 11.5-compression ratio piston. GT power simulations suggest that a low compression ratio of the high-pressure unit of DCEE could lead to an improvement in efficiency. The current study consists of two sets of experiments. In the first set of experiments, the intake pressure and intake temperatures are increased to…

Ever increasing heat flux inside combustion chamber has drawn a lot of concerns from automakers. As one of the most critical components in engines, the piston suffers periodic heat and mechanical loadings due to the prolonged expose to the high-temperature combustion gas. How to cool the piston effectively and accurately becomes one of the determining factors to ensure the reliability and durability of diesel engines. At present, there’re several approaches to remove the heat flux from the piston. The cooling gallery, as one of the most efficient cooling methods for pistons, has been widely used for their thermal managements. However, it’s really difficult to understand what really happens inside the cooling gallery, as it’s deeply located within the piston head. Although a series of experiments have been conducted in previous studies, they’re all based on a quasi-steady-state assumption. Only an average heat transfer coefficient throughout one cycle can be obtained, which fails to provide the transient flow and heat transfer processes in details. During the engine operation, the piston takes a periodic motion under the…

Previously, the authors have proposed a novel strategy called trajectory based combustion control for the free piston engine where the shape of the piston trajectory between top and bottom dead centers is used as a control input to modulate the chemical kinetics of the fuel-air mixture inside the combustion chamber. It has been shown that in case of a hydraulic free piston engine, using active motion control, the piston inside the combustion chamber can be forced to track any desired trajectory, despite the absence of a crankshaft, providing reliable starting and stable operation. This allows for the use of optimized piston trajectory for every operating point which minimizes fuel consumption and emissions. In this work, this concept is extended to an electrical free piston engine as a modular power source. A dynamic model of a linear electrical free piston engine unit has been developed which consists of a single phase linear generator driven by a single cylinder engine. The linear generator unit not only provides the required electromagnetic force to ensure precise trajectory tracking for…

This study looked into the application of active thermal coatings on the surfaces of the combustion chamber as a method of improving the thermal efficiency of internal combustion engines. The combination of low thermal conductivity and low heat capacity that these coatings are offering, reduces the temperature gradient between the hot combustion gases and the cooler surroundings during the engine cycle thus leading to lower heat transfer losses and increased piston work. The use of such coatings also results in increased exhaust temperatures which has the potential to improve the cold start performance of after-treatment systems. The active thermal coating was applied to a production aluminium piston and its performance was compared against a reference aluminium piston on a single-cylinder diesel engine. The two pistons were tested over a wide range of speed/load conditions and the effects of EGR and combustion phasing on engine performance and tailpipe emissions were also investigated. A detailed energy balance approach was also employed to study the thermal behaviour of the active thermal coating. In general, improvements in indicated specific…

The piston temperature has to be carefully controlled to achieve effective and efficient thermal management in internal combustion engines. One of the common methods to cool piston is by injecting oil from the crankcase underside to the piston under-crown area. In the present study, a novel 3D multiphase thermal-fluid coupled model is developed using the commercial CFD software SimericsMP+ to study the piston cooling using the oil jet. In this model, an algorithm is proposed to couple the fluid and solid computation domain to account for the different timescale of heat transfer in the fluid and solid due to the high thermal inertia of the solid piston. Combustion heat flux on the piston surface and the liner temperature distribution are used as the boundary conditions. The temperature-dependent material properties, piston motion, and thermal contact resistance between the ring and piston are also accounted for. The oil film on the piston under-crown area is captured in the model to ensure an accurate prediction of the heat transfer coefficient. The piston temperature from the numerical simulation is…

Low combustion efficiency and high hydrocarbon emissions at low load are key issues of natural gas and diesel dual fuel engines. For better engine performance, two diesel-spray-orientated (DSO) bowls were developed based on the existing diesel injector of a heavy-duty diesel engine with the purpose of placing more combustible natural gas/air mixture around the diesel spray jets. A bulge-ring was designed at the rim of the piston bowl to enhance the in-cylinder flame propagation. Numerical simulations were conducted for a whole engine cycle by using STAR-CD 4.22 at engine speed of 1200 r/min and indicated mean effective pressure (IMEP) of 0.6 MPa. ECFM-3Z combustion model with built-in soot emissions model was employed. In this paper, natural gas was considered as a mixture of 95% methane and 5% ethanol. Simulation results of the original piston bowl agreed well with the experimental data, including in-cylinder pressure and heat released rate, as well as soot and methane emissions. Turbulence kinetic energy, combustion efficiency and methane emissions of the DSO piston geometries were compared with that of the original…

An experimental study was conducted on a Ricardo Hydra single-cylinder light-duty diesel research engine. Start of Injection (SOI) timing sweeps from -350 deg aTDC to -210 deg aTDC were performed on a total number of five pistons including two baseline metal pistons and three coated pistons to investigate the effects of thick thermal barrier coatings (TBCs) on the efficiency and emissions of low-temperature combustion (LTC). A fuel with a high latent heat of vaporization, wet ethanol, was chosen to eliminate the undesired effects of thick TBCs on volumetric efficiency. Additionally, the higher surface temperatures of the TBCs can be used to help vaporize the high heat of vaporization fuel and avoid excessive wall wetting. A specialized injector with a 60° included angle was used to target the fuel spray at the surface of the coated piston. Throughout the experiments, the equivalence ratio, ϕ, was maintained constant at 0.4; the combustion phasing was consistently matched at 6.8 ± 0.4 deg aTDC. It can be concluded that the thick TBC cases achieved 1 to 2 percentage points…

Increasingly stringent emissions regulations in automotive applications are driving advancements in after-treatment technology and emissions control strategies. Fast warm-up of the after-treatment system during the engine cold-start is essential to meet future emissions targets. In this study, a range of strategies were evaluated on a 2.2L, four cylinder, light-duty Gasoline Compression Ignition (GCI) engine with geometric compression ratio 17. The GCI engine has a single stage turbocharger and low-pressure exhaust gas recirculation (EGR) with EGR cooler bypass. . For cold-start assist, the engine is equipped with a 2.5kW electric heater. The aftertreatment system is comprised of an oxidation catalyst, followed by a particulate filter and an SCR catalyst. A detailed GT-Power model of the GCI engine system was developed for evaluations. In the first work phase, the individual and combined benefit of the engine-based strategies, such as flare speed, load, retarded CA50, intake air heater and backpressure valve throttling were evaluated for ambient cold-start. The cumulative benefit of the strategies produced estimated exhaust temperature and exhaust enthalpy of 470 degree C and 10 kW, respectively…

We have proposed a new compressive combustion principle based on pulsed supermulti-jets colliding through focusing process, by injection from chamber wall to chamber center. This principle has potential of relatively-silent high compression around chamber center because of auto-ignition far from chamber wall and nearly-complete air insulation due to encasing of burned high temperature gas. The present principle leading to higher thermal efficiency and higher power will be applicable for automobiles, aircrafts, rockets, and also flying cars to be realized in the future. Then, water cooling system made smaller or even eliminated will result in lower price, while auto-ignition in an area larger than that created by traditional spark-ignition will lead to less NOx emission at very lean burning. Thus, we here show four new evidences based on experimental data and computational and theoretical considerations. (1) Quantitative clarification of compression level at condition without combustion (2) Atomization effect due to high-speed jets reducing fuel tank pressure (3) Combustion experiments in piston-less engine having pulsed 14-focusing jets colliding (1st prototype engine for checking this compressive combustion principle),…