Automotive Engine Combustion Research Articles

Ion Current Simulation Model Design for a Spark-Ignited Engine

The use of ion current signals generated during the combustion process of mixed gas as a function of initial mixture composition, temperature and pressure to detect cylinder combustion states is the most recent approach in the design, development, and optimisation of automotive engine combustion control. This paper aims to design predictive identification and computationally fast and accurate ion current models for obtaining combustion information in the engine cylinder in real time. To build a more comprehensive ion current calculation model, the effect of the flame ionisation process, the geometry of the spark plugs, and the combustion pressure and temperature are considered in the new building ion current model. The simulation ion current waveform, which has a double-peak structure, is in good agreement with the experiment values; thus, the ion current model has the potential to be used for real-time control and optimisation of engine cylinder combustion.

Experimental study of pulsed microwave discharges at pressures ranging over five orders of magnitude

Microwave discharge igniter (MDI) is a discharge system developed to initiate combustion in automotive engines. The MDI uses a sequence of N = 700 microwave (2.45 GHz) pulses 100 ns in duration separated by 1 μs. The initial breakdown is provided by the first microwave pulse, 5 μs in duration. The aim of pulsing the microwave signal is to keep an optimal combination of parameters when, even at elevated pressures, (i) the discharge propagates over the largest possible volume; (ii) the plasma is non-equilibrium. Properties of plasma produced by MDI igniter in non-combustible gas mixtures at ambient gas temperature and gas pressure in the range between 0.2 mbar and 8 bar were studied experimentally. Discharge spatial structure was analyzed with the help of time-resolved ICCD imaging. Near-UV optical emission spectra taken in different pulses provided the information about rotational and vibrational temperatures. The electric field was estimated on the basis of ratio of emission of the second positive and the first negative systems of molecular nitrogen.

自動車エンジン燃焼解析ソフトウェアHINOCA（火神）の開発

自動車エンジン燃焼解析ソフトウェアHINOCA（火神）の開発

On Beneficial Mode Switch Decisions based on Short-term Engine Load Prediction

Multimode combustion in automotive engines have the potential to increase fuel efficiency by choosing the best combustion mode at each operating condition. When switches among the combustion modes are neither instantaneous nor lossless, a mode switch can only be beneficial if the associated residence time in the target mode is long enough to compensate for the fuel penalty of the switch. An accurate engine load prediction over a short-term horizon is thus necessary for deciding on a beneficial mode switch. This paper addresses this. In the application of spark ignited (SI) and homogeneous charge compression ignition (HCCI) combustion modes, prior work quantified fuel efficiency benefits and mode switch penalties. In this paper, it is estimated that, to result in a fuel economy benefit, the residence time in HCCI mode is required to be longer than 1.2 s. If it is possible to accurately predict engine load over such a time horizon, an optimal mode switch decision could be made. To this end, five receding horizon prediction methods, based on artificial neural networks and polynomial extrapolation, are tested with vehicle measurement data and compared in terms of their accuracy in predicting engine load as well as HCCI entry and exit events. It is shown that although the prediction accuracy is very low for visitations of the HCCI regime around 1.2 s, all the methods are able to determine if an immediate entry of exit will occur, and if a HCCI visitation is going to be very short. This finding is applied in a basic mode switch decision structure.

Mixture of glycerol ethers as diesel bio-derivable oxy-fuel: Impact on combustion and emissions of an automotive engine combustion system

The effects on combustion and emissions of a bio-derivable glycerol-based ethers mixture (GEM) usable in a compression ignition engine have been investigated. The tests were performed on a single cylinder research engine derived from a Euro5 compliant four cylinder engine for passenger car application. The experimental methodology has considered the comparison among three fuels: (1) a reference diesel; (2) a mixture consisting of 90vol.% diesel and 10vol.% of GEM; (3) a blend consisting of 80vol.% diesel and 20vol.% of GEM. The tests were carried out in some characteristic key points of the New European Driving Cycle (NEDC) emission homologation cycle. These points allowed an estimation of the blend impact on the performance of a real four-cylinder engine (one cylinder of which is represented by the research engine) over the NEDC. Both regulated and unregulated pollutant emissions have been measured during the test campaign. In particular, apart from the regulated emissions, the concentration of aldehydes and carbonaceous particles at the engine exhaust has been determined in some test points. The results have shown the possibility to burn the diesel/GEM blends without any significant impact on combustion characteristics and efficiencies, while, due to the oxygen content of the GEM, important benefits were obtained in terms of NOx-PM trade-off and emissions of particles at the exhaust. At medium–high load conditions, there was a maximum decrease of about 70% in terms of PM emissions compared to a slight increase of NOx. At low load conditions, a maximum increase of HC and CO of about 50% has been detected. Regarding the emissions of aldehydes, the results showed that the GEM addition favoured the increasing of carbonyl compounds at low engine loads, while at higher loads no significant variation has been detected by burning GEM.

Physical Properties of Hydrocarbon Oils Produced by Botryococcus Braunii: Density, Kinematic Viscosity, Surface Tension, and Distillation Properties

In automotive engine combustion, particularly in case of compression ignition in diesel engines, physical properties of the fuel have a direct impact on the spray combustion process. The density, kinematic viscosity, surface tension, and distillation properties of triterpenic hydrocarbons extracted from the BOT-22 strain of Botryococcus braunii (called Bot-oil) were measured, and these properties were compared with those of standard diesel fuel. The density and surface tension of Bot-oil were almost the same as those of the diesel fuel. However, the kinematic viscosity of Bot-oil was 55 to 58 cSt at room temperature, which was 16 times higher than that of the diesel fuel. In addition, the distillation temperature of Bot-oil was approximately 430 °C, which was over 100 °C higher than that of the diesel fuel. To attain the properties required for fuel, a cracking technology for Bot-oil must be established.

Reduction of kinetic mechanisms for fuel oxidation through genetic algorithms

New automotive engine combustion concepts, such as the Homogeneous Charge Compression Ignition (HCCI) or the Controlled Autoignition (CAI), have been developed in the last years in order to fulfil the very stringent European regulations limiting pollutant emissions (mainly nitrogen oxides and particulate matter). These combustion modes are not controlled by the physical phenomena prior to combustion, as usual in traditional Compression Ignition (CI) and Spark Ignition (SI) engines, but by the fuel chemical kinetics leading to autoignition, which is described by the corresponding reaction mechanism. Since the detailed reaction mechanism of surrogate fuels (which are used instead of the original fuels in order to simulate their oxidation process) consists of hundreds of species and thousands of reactions, it cannot be used for engine simulation purposes due to the very excessive computational time requirements. Thus, reduced reaction mechanisms, which simulate properly some characteristics of the detailed one (autoignition time, combustion temperature, etc.), are used instead. Among the typical reduction techniques (Quasi-Steady-State Assumption (QSSA), Reaction Analysis, etc.), Genetic Algorithms (GA) allow for both an efficient reduction of small/medium size reaction mechanisms and, when combined with other techniques, a more effective reduction of large reaction mechanisms. In this work, a general and innovative GA methodology for the reduction of kinetic mechanisms describing the hydrocarbon oxidation processes has been proposed, and its application to the reduction of two different mechanism sizes (a medium one describing the methane autoignition and a larger one derived from the oxidation of a diesel fuel surrogate) has provided better results when compared to other GA methodologies or reduction techniques. The reduced mechanisms provide very similar autoignition time and combustion temperature values to those obtained from the detailed mechanism under different engine operating conditions (intake pressure and temperature, equivalence fuel/air ratio and exhaust gas recirculation rate).

Impact of acetaldehyde and NO addition on the 1-octene oxidation under simulated HCCI conditions

Due to more and more stringent restrictions on vehicle exhaust emissions, low temperature combustion in automotive engines becomes more and more important. Low temperature combustion is achieved by high rates of Exhaust Gas Recirculation (EGR). EGR gases are used to dilute the fuel/air mixture in the engine and to control ignition delay times. However, nowadays, EGR is also supposed to have chemical impact on the Homogeneous Charge Compression Ignition (HCCI) engine combustion. First, the effects of NO and acetaldehyde addition were studied performing HCCI engine experiments with different concentrations of NO and CH 3CHO. Since the impact of EGR compounds on engine control is difficult to understand in an engine itself, experiments were performed in a Jet-Stirred Reactor (JSR) where conditions are well-controlled. The effects of the addition of NO (100 ppm) and acetaldehyde (200 ppm) on 1-octene oxidation were studied at 1.013 MPa, under dilute conditions. According to the literature, a complex impact of NO was observed, but in contrast to the assumption that aldehydes could have a strong impact on oxidation kinetics, only moderate effects of acetaldehyde were found but leading to a significant impact on combustion in an HCCI engine. However, a synergy between NO and acetaldehyde on the oxidation of 1-octene was observed when these species were added simultaneously leading to an inhibition of fuel oxidation at low temperatures, an important reduction of the NTC-effect, and a promotion of fuel oxidation in higher temperatures. These results tend to demonstrate the importance of taking into account the complexity of EGR composition.