Engine designers face a gathering storm...and it’s starting to rain, says Reaction Design CEO Bernie Rosenthal. The high-level clouds are global warming concerns and material and financial scarcity, while engine designers have to contend with a plethora of resulting requirements: engine down-sizing/hybridization; new fuel sources; changing fuel composition; cost constraints; particle size and umber limits; tighter emissions regulations; stringent engine-control requirements; and fuel efficiency requirements.

The response has been to increase engine complexity with the solutions that designers are coming up with—for example, charge compression ignition, either homogeneous or partially premixed, or new dual fuels concepts. We’re starting to see another layer of complexity. All these things are very hard to test...very costly to test if you wait until you have a prototype. We believe that simulation is becoming more and more at the forefront of where engine designers are trying to get to.

Practice shows that existing CFD tools can’t handle realistic fuel chemistry required for accurate emissions and efficiency predictions. FORTÉ gives designers the ability to model efficient engines that are able to take advantage of the broadening fuels landscape while meeting increasingly strict emissions standards.

—Bernie Rosenthal, CEO of Reaction Design

Seeking feedback from engine designers on their current tools, Reaction Design found that:

• Designers can’t use their existing tools to predict fuel effects/emissions. Time-to-solution is prohibitively long, and emissions models (especially soot) give wrong trends/results.

• The CFD companies they currently work with cannot help them with chemistry

• Too much fitting/calibration was needed to match real data; current CFD is not sufficiently predictive.

• Too much time is spent generating CFD meshes.

• Designers employ multiple/different software tools to get their jobs done, including visualization and comparison of results to experimental data.

To deal with the challenge, designers are relying on iterations of non-reacting flow simulations and experimental testing; using severely reduced/simplified mechanism and handling chemistry with look--up tables; relying only on experimental testing to try to understand real fuel effects; and/or ignoring emissions in cylinder and dealing with them only in the aftertreatment system. The result, says Rosenthal, has been a trade-off between accuracy and time-to-solution. An accurate model, he notes, should predict engine outputs based on engine inputs, with a minimized need to calibrate model parameters.

RD/WERC joint venture yields spray model that does not require excessive grid refinement near the droplets. Source: Reaction Design. Click to enlarge.

Through a joint venture between Reaction Design and Wisconsin Engine Research Consultants (WERC), FORTÉ CFD integrates unique “grid independent” spray models that greatly reduce the amount of calibration required for predicting engine performance. These high-fidelity spray models also allow real fuel analysis by matching multi-component physical properties with a multi-component chemistry model.

Generating the computational meshes required for internal combustion engine simulations have traditionally required expert personnel and long cycle times. Some commercially available CFD packages use automatic meshing techniques that claim to reduce the time and expertise required to create a mesh. These solutions often add more complexity to the problem that can actually increase the overall time-to-solution and affect the accuracy of the calculations. FORTÉ CFD includes a novel and proprietary automated mesh generator that, combined with the advanced mesh independent spray models, produces accurate meshes without compromising run time or solution accuracy.

FORTÉ benchmarks: PCCI PRF+Ethanol. Blue line= FORTÉ CFD. Red line = reduced mechanism without FORTÉ solver. Triangles = experimental data. Source: Reaction Design. Click to enlarge.

Benchmark tests have shown that FORTÉ CFD delivers more accurate predictions of basic combustion characteristics, such as ignition timing, knocking tendency and pollutant and soot emissions, when compared to other CFD software products. FORTÉ CFD also allows simulation of advanced engine concepts promising dramatic efficiency improvements, such as Premixed or Homogeneous Charge Compression Ignition (PCCI or HCCI) and dual-fuel engines.

Key features of FORTÉ CFD include:

• Proprietary combustion chemistry solver: Employing industry leading numerical solution methods, FORTÉ CFD is the only commercial CFD software that supports the modeling of real fuel chemistry effects with acceptable time-to-solution metrics.

• Advanced spray models: High-fidelity spray models provide mesh-independent results and account for multi-component fuel-vaporization effects and flash boiling, as well as state-of-the-art droplet breakup and collision effects.

• Automatic mesh generation: Starting from a CAD description of the geometry, FORTÉ CFD creates a Cartesian mesh that is dynamic, adapts on-the-fly, and is fully automated throughout the piston cycle.

If you look at the world situation, we could sorely use some new and more efficient technology as quickly as possible.

—Bernie Rosenthal

Reaction Design’s FORTÉ CFD product for predictive engine simulation is available now.