International Journal of Engine Research

Variable geometry turbine is a technology that has been proven on diesel engines. However, despite the potential to further improve gasoline engines’ fuel economy and transient response using variable geometry turbine, controlling the variable geometry turbine during transients is challenging due to its highly non-linear behaviours especially on gasoline applications. After comparing three potential turbocharger transient control strategies, the one that predicts the turbine performances for a range of possible variable geometry turbine settings in advance was developed and validated using a high-fidelity engine model. The proposed control strategy is able to capture the complex transient behaviours and achieve the optimum variable geometry turbine trajectories. This improved the turbocharger response time by more than 14% compared with a conventional proportional–integral–derivative controller, which cannot achieve target turbocharge speed in all cases. Furthermore, the calibration effort required can be significantly reduced, offering significant benefits for powertrain developers. It is expected that the structure of this transient control strategy can also be applied to complex air-path systems.

It is of interest for engine combustion modeling to quantify the evaporation behaviors of fuel spray impinging on a wall as the fuel atomization, evaporation, and mixing with oxygen in the combustion chamber usually dominate the subsequent combustion processes. In this study, the vapor and liquid mass distributions in diesel-like fuel sprays were quantified using the ultraviolet-visible laser absorption scattering imaging technique. The sprays were injected from a single-hole nozzle with a common-rail injection system and impinged on a flat wall at an ambient pressure of 4 MPa and an ambient temperature of 833 K. The mass of the total fuel vapor, the spray volume covered by the vapor phase, and the air mass entrained into the spray were characterized. The results indicate that the time evolution of these parameters until shortly after the end of injection can be expressed by a power-law function, Y_i = k_i·t_s^1.5, where Y_i represents the parameter like vapor mass and so on, t_s is the time after start of injection, and k_i is the coefficient corresponding to Y_i. The physics behind this power-law function was analyzed and discussed based on the theory of atomization and evaporation, and verified using measurement data obtained under different conditions of injection quantity.

This article employs a mixed lubrication model to investigate the performance of the textured surface. The Jakobsson–Floberg–Olsson model is used to obtain the hydrodynamic support of the textured conjunction, while the calculation of the asperity contact load is based on the load-sharing concept. Based on the simulated Stribeck curves of the smooth surface and the textured surface, comparisons are conducted to study the effect of texturing under different lubrication regimes. It appears that the transition of lubrication regimes is influenced by the texturing parameters and the convergence degrees of conjunction. The presence of textures delays the appearance of the mixed lubrication regime and the boundary lubrication regime.

In internal combustion engines, cycle-to-cycle and cylinder-to-cylinder variations of the combustion process have been shown to negatively impact the fuel efficiency of the engine and lead to higher exhaust emissions. The combustion variations are generally tied to differences in the composition and condition of the trapped mass throughout each cycle and across individual cylinders. Thus, advanced engines featuring exhaust gas recirculation, flexible valve actuation systems, advanced fueling strategies, and turbocharging systems are prone to exhibit higher variations in the combustion process. In this study, the cylinder-to-cylinder variations of the combustion process in a dual-fuel internal combustion engine leveraging late intake valve closing are investigated and a model to predict and address one of the root causes for these variations across cylinders is developed. The study is conducted on an inline six-cylinder heavy-duty dual-fuel engine equipped with exhaust gas recirculation, a variable geometry turbocharger, and a fully flexible variable intake valve actuation system. The engine is operated with late intake valve closure timings in a dual-fuel combustion mode in which a high reactivity fuel is directly injected into the cylinders and a low reactivity fuel is port injected into the cylinders. The cylinder-to-cylinder variations observed in the study have been associated with the maldistribution of the port-injected fuel, which is exacerbated at late intake valve timings. The resulting difference in indicated mean effective pressure between the cylinders ranges from 9% at an intake valve closing of 570° after top dead center to 38% at an intake valve closing of 620° after top dead center and indicates an increasingly uneven fuel distribution. The study leverages both experimental and simulation studies to investigate the distribution of the port-injected fuel and its impact on cylinder-to-cylinder variation. The effects of intake valve closing as well as the impact of intake runner length on fuel distribution were quantitatively analyzed, and a model was developed that can be used to accurately predict the fuel distribution of the port-injected fuel at different operating conditions with an average estimation error of 1.5% in cylinder-specific fuel flow. A model-based control strategy is implemented to adjust the fueling at each port and shown to significantly reduce the cylinder-to-cylinder variations in fuel distribution.

Referring to spark-ignition engines, the downsizing, coupled to turbocharging and variable valve actuation systems are very common solutions to reduce the brake-specific fuel consumption at low-medium brake mean effective pressure. However, the adoption of such solutions increases the complexity of engine control and management because of the additional degrees of freedom, and hence results in a longer calibration time and higher experimental efforts. In this work, a twin-cylinder turbocharged variable valve actuation spark-ignition engine is numerically investigated by a one-dimensional model (GT-Power^™). The considered engine is equipped with a fully flexible variable valve actuation system, realizing both a common full-lift strategy and a more advanced early intake valve closure strategy. Refined sub-models are used to describe turbulence and combustion processes. In the first stage, one-dimensional engine model is validated against the experimental data at full and part load. The validated model is then integrated in a multipurpose commercial optimizer (modeFRONTIER^™) with the aim to identify the engine calibration that minimizes brake-specific fuel consumption at part load. In particular, the decision parameters of the optimization process are the early intake valve closure angle, the throttle valve opening, the turbocharger setting and the spark timing. Proper constraints are posed for intake pressure in order to limit the gas-dynamic noise radiated at the intake mouth. The adopted optimization approach shows the capability to reproduce with good accuracy the experimentally identified calibration. The latter corresponds to the numerically derived Pareto frontier in brake mean effective pressure–brake specific fuel consumption plane. The optimization also underlines the advantages of an engine calibration based on a combination of early intake valve closure strategy and intake throttling rather than a purely throttle-based calibration. The developed automatic procedure allows for a ‘virtual’ calibration of the considered engine on completely theoretical basis and proves to be very helpful in reducing the experimental costs and the engine time-to-market.

In this work, we study the effects of injector nozzle inclusion angle, injection pressure, boost, and swirl ratio on gasoline compression ignition combustion. Closed-cycle computational fluid dynamics simulations using a 1/7th sector mesh representing a single cylinder of a four-cylinder 1.9 L diesel engine, operated in gasoline compression ignition mode with 87 anti-knock index (AKI) gasoline, were performed. Two different operating conditions were studied—the first is representative of idle operation (4 mg fuel/cylinder/cycle, 850 r/min), and the second is representative of a low-load condition (10 mg fuel/cylinder/cycle, 1500 r/min). The mixture preparation and reaction space from the simulations were analyzed to gain insights into the effects of injection pressure, nozzle inclusion angle, boost, and swirl ratio on achieving stable low-load to idle gasoline compression ignition operation. It was found that narrower nozzle inclusion angles allow for more reactivity or propensity to ignition (determined qualitatively by computing constant volume ignition delays) and are suitable over a wider range of injection timings. Under idle conditions, it was found that lower injection pressures helped to reduce overmixing of the fuel, resulting in greater reactivity and ignitability (ease with which ignition can be achieved) of the gasoline. However, under the low-load condition, lower injection pressures did not increase ignitability, and it is hypothesized that this is because of reduced chemical residence time resulting from longer injection durations. Reduced swirl was found to maintain higher in-cylinder temperatures through compression, resulting in better ignitability. It was found that boosting the charge also helped to increase reactivity and advanced ignition timing.

The use of a knock intensity threshold set at a relatively high level is effective for identifying knocking cycles, but results in high Type II (false negative) classification errors. Many cycles, although classified as non-knocking cycles (i.e. below the threshold), are actually operating in an undesirably high knock rate region. A traditional controller is therefore likely to advance the spark further into this region, when the correct response would be to retard the spark. In this article, a new dual-threshold knock controller is presented in which a second threshold is introduced in order to identify non-knocking cycles more clearly. This enables the advance gain to be increased without adversely affecting other aspects of the response, thereby improving the transient and steady-state performance characteristics of the controller. The threshold values can also be optimized so as to minimize the total Type I and Type II misclassification errors, resulting in a significant improvement in most aspects of the controller response.

Premixed charge compression ignition (PCCI) is a promising combustion strategy for reducing in-cylinder NO_x and particulate matter formation in diesel engines without incurring fuel penalty. However, one of the challenges in PCCI implementation is that the process does not allow direct control of the combustion timing. The crank angle of 50% heat release, known as the CA50, is generally a reasonable proxy for the quality of combustion in terms of maximum pressure rise rate, combustion noise, and fuel conversion efficiency. This paper outlines the development, and validation, of a real-time capable estimation strategy for diesel-fueled PCCI CA50 using production-viable measurements that do not include in-cylinder pressure. The CA50 estimation strategy considers both stages of diesel-fueled PCCI combustion—low-temperature heat release and high-temperature heat release, which contributes most to the cumulative heat released during combustion. The strategy is validated using a PCCI CA50 dataset generated with a wide range of positions of a variable geometry turbocharge, exhaust gas recirculation fractions, and intake valve closing timings. The model estimates CA50 within ±2 CAD for 65 out of 80 data points and exhibits an error standard deviation of 2.55 CAD.

Better knowledge of the instantaneous soot and nitrogen oxides (NO _x ) emissions in Diesel engines would allow better choices of injection parameters and thus lead to better raw emissions than, for instance, with classical averaged measures, like smoke maps. Unfortunately, while for most regulated emissions fast measurements are possible and reasonably fast sensors are available, the same is not true for soot. Against this background, this paper proposes a real time, delay-free soot model based on the pressure trace information. The model essentially maps changes of the pressure trace into changes of the raw soot emissions. The key elements of the approach are the design of experiments, segmentation of the pressure trace and the use of the principal component analysis technique to extract the essential information. The model is based only on data; that is, it needs an initial calibration with working points measured with a standard device, such as an AVL Microsoot or Opacimeter. This paper describes the method and then shows validation results with an additional amount of pilot injection in one cylinder which confirms the delay-free soot estimation.