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In spark-ignition engines, fluctuations of the in-cylinder pressure trace and the apparent rate of heat release are usually observed from one cycle to another. These Cycle-to-Cycle Variations (CCV) are affected by the early flame development and the subsequent flame front propagation. The CCV are responsible for engine performance (e.g. fuel consumption) and the knock behavior. The occurrence of the phenomena is unpredictable and the stochastic nature offers challenges in the optimization of engine control strategies. In the present work, CCV are analyzed in terms of their impact on the engine knock behavior and the related efficiency. Target is to estimate the possible fuel consumption savings in steady-state operation and in the drivecycle, when CCV are reduced. Since CCV are immanent on real engines, such a study can only be done by means of simulation.

Spark Ignited (SI) combustions engines in combination with different degrees of hybridization are expected to play a major role in future vehicle propulsion. Due to the combustion principle and the related thermodynamic efficiency, it is especially challenging to meet future CO2 targets. The layout and optimization of the overall system requires novel methods in the development process which feature a seamless transition between real and virtual prototypes. Herein, engine models need to predict the entire engine operating range in steady-state and transient conditions and must respond to all relevant control inputs. In addition, the model must feature true real-time capability. This work presents a holistic and modular modeling framework, which considers all relevant processes in the complex chain of physical effects in SI combustion.

Today unmanned aerial vehicle applications are powered by Wankel rotary engines due to their high power-to-weight ratio and smooth operation. Most of modern propulsion units for unmanned aerial vehicles are designed to run on high volatile fuels such as aviation gasoline (AvGas). However, the refueling infrastructure in aviation is geared toward the most used aviation fuel, kerosene. This and other reasons, such as significantly lower price and easier fire protection regulations, lead to the desire to be able to operate these propulsion units with kerosene. Opposed to reciprocating engines, the low compression ratio of rotary engines prevents the implementation of compression ignition combustion processes. Therefore, the purpose of this paper is to discuss the operation of a spark-ignited rotary engine on different fuels. In detail, different qualities of kerosene as well as gasoline/kerosene blends are compared together.

Unstable combustion and high cyclic variations of the in-cylinder pressure associated with low engine running smoothness and high emissions are mainly caused by cyclic variations of the fresh charge composition, the variability of the ignition and the fuel mass. These parameters affect the inflammation, the burn rate and thus the whole combustion process. In this paper, the effects of fluctuating fuel mass on the combustion behavior are shown. Small two-stroke engines require special measuring and testing equipment, especially for measuring the fuel consumption at very low fuel flow rates as well as very low fuel supply pressures. To realize a cycle-resolved measurement of the injected fuel mass, fuel consumption measurement with high resolution and high dynamic response is not enough for this application.

The piston ring and cylinder liner tribosystem is very sensitive. It is a heavily loaded system with high temperature and force exposure. High demands are made on the components in this area. These facts concern not only system components, but also the engine oil which can reach up to 300°C at the inner cylinder walls. High temperatures and force cause oil aging. As a part of the combustion chamber, the piston ring-cylinder liner tribosystem is in close contact with combustion constituents. If alternative fuels like ethanol are used, the influences to this tribosystem have to be investigated. In particular, the impacts of oil aging have to be considered to avoid higher wear and damage to the engine, to assure low fuel consumption, and to extend oil change intervals. Research work on abrasion of the ring-cylinder system was aimed to gain detailed information about the effects on this tribosystem.

This study presents a methodology to predict particle number (PN) generation on a naturally aspirated 4-cylinder gasoline engine with port fuel injection (PFI) from wall wetting, employing numerical CFD simulation and fuel film analysis. Various engine parameters concerning spray pattern, injection timing, intake valve timing, as well as engine load/speed were varied and their impact on wall film and PN was evaluated. The engine, which was driven at wide open throttle (WOT), was equipped with soot particle sampling technology and optical access to the combustion chamber of cylinder 1 in order to visualise non-premixed combustion. High-speed imaging revealed a notable presence of diffusion flames, which were typically initiated between the valve seats and cylinder head. Their size was found to match qualitatively with particulate number measurements. A validated CFD model was employed to simulate spray propagation, film transport and droplet impingement.

A naturally aspirated SI engine with port fuel injection was investigated at the Institute for Powertrains and Automotive Technology of the Vienna University of Technology to analyze the impact of the ethanol blend E85 on the full load performance. Measurements and numerical studies with a predictive wall film model have been carried out to explain the mixture cooling, the calorific fluid properties after inlet valve closing and the volumetric efficiency with conventional fuel and E85. It could be shown that only with a detailed modelling of the wall film formation in the inlet port an accurate prediction of the engine's full load performance is possible when studying different fuels with varying fluid properties. Anyway, an integrated approach that includes measurements and numerical investigations is necessary to analyse the mixture preparation and the engine process correctly.

Today's calibration process for ECU functions is often based on a wide variety of proprietary tools and individual expert knowledge of calibration engineers. Automatic calibration with an industrialized tool chain provides high potential to reduce testbed time, calibration time and project costs. Based on an efficient measurement procedure in combination with an offline calibration methodology the capability is validated, e.g. for calibrating the ECU function “Air Charge Determination” for SI engines. In this article the implementation, in a series production project of a major OEM, is shown. The whole workflow - which can also be applied to other calibration tasks - will be described in detail. Presented here will be how General Motors Corporation (GM) is able to speed up the calibration of the ECU functions, whilst maintaining at least the same quality of calibration as before, by the use of this tool chain.

The present paper deals with the application of the LES approach to in-cylinder flow modeling. The main target is to study cycle-to-cycle variability (CCV) using 3D-CFD simulation. The engine model is based on a spark-ignited single-cylinder research engine. The results presented in this paper cover the motored regime aiming at analysis of the cycle-resolved local flow properties at the spark plug close to firing top dead center. The results presented in this paper suggest that the LES approach adopted in the present study is working well and that it predicts CCV and that the qualitative trends are in-line with established knowledge of internal combustion engine (ICE) in-cylinder flow. The results are evaluated from a statistical point of view based on calculations of many consecutive cycles (at least 10).

The shift toward electrification and limitations in battery electric vehicle technology have led to high demand for hybrid vehicles (HEVs) that utilize a battery and an internal combustion engine (ICE) for propulsion. Although HEVs enable lower fuel consumption and emissions compared to conventional vehicles, they still require combustion of fuels for ICE operation. Thus, emissions from hybrid vehicles are still a major concern. Engine starts are a major source of emissions during any driving event, especially before the three-way catalyst (TWC) reaches its light-off temperature. Since the engine is subjected to multiple starts during most driving events, it is important to mitigate and better understand the impact of these emissions. In this study, experiments were conducted to analyze engine starts in a hybrid powertrain on different experimental setup.