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Technical Paper

Improving NOx and Fuel Economy for Mixture Injected SI Engine with EGR

A large quantity of recirculated exhaust gas is used to reduce NOx emissions and improve fuel economy at the same time. The effect of exhaust gas recirculation (EGR) was investigated under the stoichiometric and lean operating conditions and compared with the effect of lean operation without EGR. A mixture injected SI engine that has a mechanically driven mixture injection valve installed was prepared. In this engine, it is possible to charge combustible mixture independently from combustion air and recirculated exhaust gas introduced from intake port in order to stratify the mixture. The effect of the EGR ratio on NOx emissions and fuel consumption was measured under the stoichiometric and lean operating conditions. Due to the mixture distribution controlled by the mixture injection, a large quantity of recirculated exhaust gas could be introduced into the combustion chamber under the stoichiometric air/fuel ratio. The limit of EGR ratio was 48 %.
Technical Paper

Development of the Stratified Charge and Stable Combustion Method in DI Gasoline Engines

The new combustion method in DISC engine has been developed. It has a double structure combustion chamber characterized as ‘Caldera’. The chamber is constructed by a center cavity for the purpose of forming a stable mixture around a spark plug electrode, and by an outer cavity which has a role of a main chamber. This method makes possible a perfect un-throttling operation, and a fuel consumption equal to a diesel engine is achieved. With regard to an out-put of DISC engine, a stoichmetric combustion and a high torque are achieved by controling a fuel injection timing with an electro-magnetic injection system device. With regard to emission regulations, a heavy EGR include residual gas decreases greatly NOx and HC emissions simultaneously, and which suggests a possibility to achieve LEV/ULEV regulations.
Technical Paper

Development of Low Particulate Engine with Ceramic Swirl Chamber

An all-ceramic swirl chamber has been developed which meets the 1987 U.S. particulate emission standard for LDV. The all ceramic construction raises combustion temperature to reduce particulate emission to the necessary level. But particulate reduction led to two-fold increase in NOx. This problem was coped with by applying EGR and fuel injection timing control. As a result NOx has been cut to the same level as with a base engine and particulate has been further reduced.
Technical Paper

Knock in Spark Ignition Engines

The knocking characteristics of several fuels are studied using a single cylinder test engine with variations in key engine operating parameters. Compression ratio, spark advance, fuel equivalence ratio, exhaust gas recirculation, engine speed, charge inlet pressure and charge inlet temperature were varied to yield a range of engine cylinder pressure-temperature histories as the base for this study. The fuels studied include three reference fuels containing isooctane and heptane with isooctane volume percents of 80, 90 and 100. Two wide boiling range gasolines were also studied. A number of empirical relationships for autoignition times of isooctane and heptane blends are employed in conjunction with the experimentally obtained pressure-temperature histories to predict onset of knock. The accuracies of the predictions with respect to the experimentally determined knock points are discussed.
Technical Paper

On the Maximum Pressure Rise Rate in Boosted HCCI Operation

This paper explores the combined effects of boosting, intake air temperature, trapped residual gas fraction, and dilution on the Maximum Pressure Rise Rate (MPRR) in a boosted single cylinder gasoline HCCI engine with combustion controlled by negative valve overlap. Dilutions by both air and by cooled EGR were used. Because of the sensitivity of MPRR to boost, the MPRR constrained maximum load (as measured by the NIMEP) did not necessarily increase with boosting. At the same intake temperature and trapped residual gas fraction, dilution by recirculated burn gas was effective in reducing the MPRR, but dilution by air increased the value of MPRR. The dependence of MPRR on the operating condition was interpreted successfully by a simple thermodynamic analysis that related the MPRR value to the volumetric heat release rate.
Technical Paper

The Anatomy of Knock

The combustion process after auto-ignition is investigated. Depending on the non-uniformity of the end gas, auto-ignition could initiate a flame, produce pressure waves that excite the engine structure (acoustic knock), or result in detonation (normal or developing). For the “acoustic knock” mode, a knock intensity (KI) is defined as the pressure oscillation amplitude. The KI values over different cycles under a fixed operating condition are observed to have a log-normal distribution. When the operating condition is changed (over different values of λ, EGR, and spark timing), the mean (μ) of log (KI/GIMEP) decreases linearly with the correlation-based ignition delay calculated using the knock-point end gas condition of the mean cycle. The standard deviation σ of log(KI/GIMEP) is approximately a constant, at 0.63. The values of μ and σ thus allow a statistical description of knock from the deterministic calculation of the ignition delay using the mean cycle properties
Technical Paper

Numerical Simulation on Soot Formation in Diesel Combustion by Using a CFD Code Combined with a Parallelized Explicit ODE Solver

The objective of the present study is to analyze soot formation in diesel engine combustion by using multi-dimensional combustion simulations with a parallelized explicit ODE solver. Parallelized CHEMEQ2 was used to perform detailed chemical kinetics in KIVA-4 code. CHEMEQ2 is an explicit stiff ODE solver developed by Mott et al. which is known to be faster than traditional implicit ODE solvers, e.g., DVODE. In the present study, about eight times faster computation was achieved with CHEMEQ2 compared to DVODE when using a single thread. Further, by parallelizing CHEMEQ2 using OpenMP, the simulations could be run not only on calculation servers but also on desktop machines. The computation time decreases with the number of threads used. The parallelized CHEMEQ2 enabled combustion and emission characteristics, including detailed soot formation processes, to be predicted using KIVA-4 code with detailed chemical kinetics without the need for reducing the reaction mechanism.
Technical Paper

Modeling of Engine-Out Hydrocarbon Emissions for Prototype Production Engines

A model has been developed which predicts engine-out hydrocarbon (HC) emissions for spark-ignition engines. The model consists of a set of scaling laws that describe the individual processes that contribute to HC emissions. The model inputs are the critical engine design and operating variables. This set of individual process scaling relations was then calibrated using production spark-ignition engine data at a fixed light-load operating point. The data base consisted of engine-out HC emissions from two-valve and four-valve engine designs with variations in spark timing, valve timing, coolant temperature, crevice volume, and EGR, for five different engines. The model was calibrated separately for the three different engines to accommodate differences in engine design details and to determine the relative magnitudes of each of the major sources. A good fit to this database was obtained.
Journal Article

EGR Effects on Boosted SI Engine Operation and Knock Integral Correlation

The effects of cooled exhaust gas recirculation (EGR) on a boosted direct-injection (DI) spark ignition (SI) engine operating at stoichiometric equivalence ratio, gross indicated mean effective pressure of 14-18 bar, and speed of 1500-2500 rpm, are studied under constant fuel condition at each operating point. In the presence of EGR, burn durations are longer and combustion is more retard. At the same combustion phasing, the indicated specific fuel consumption improves because of a decrease in heat loss and an increase in the specific heat ratio. The knock limited spark advance increases substantially with EGR. This increase is due partly to a slower combustion which is equivalent to a spark retard, as manifested by a retarded value of the 50% burn point (CA50), and due partly to a slower ignition chemistry of the diluted charge, as manifested by the knock limited spark advance to beyond the value offered by the retarded CA50.
Journal Article

On the High Load Limit of Boosted Gasoline HCCI Engine Operating in NVO Mode

The high load limit of a boosted homogeneous-charge-compression-ignition (HCCI) engine operating on negative-valve-overlap (NVO) was assessed. When operating under stoichiometric condition with no external dilution, the load, as measured by the net indicated mean effective pressure (NIMEP), increased with increase in manifold absolute pressure (MAP), and with decrease in trapped amount of residual gas. The maximum pressure rise rate (MPRR), however, also increased correspondingly. When the MAP and the amount of residual gas were adjusted so that the engine operating point could be held at a constant MPRR value, the NIMEP increased with the simultaneous decrease in MAP and residual until the misfire limit was reached. Therefore if a MPRR ceiling is imposed, the high load limit of an HCCI engine is at the intersection of the constraining MPRR line and the misfire line.