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Technical Paper

Particle Reduction in LPG Lean Stratified Combustion by Intake Strategies

Lean stratified combustion shows high potential to reduce fuel consumption because it operates without the intervention of a throttle valve. Despite its high fuel economy potential, it emits large amounts of particulate matter (PM) because the locally rich mixture is formed at the periphery of a spark plug. Furthermore, the combustion phasing angle is not realized at MBT ignition timing, which can bring high work conversion efficiency. Since PM emission and work conversion efficiency are in a trade-off relation, this research focused on reducing PM emission through achieving high work conversion efficiency. Two intake air control strategies were examined in this research; throttle operation and late intake valve closing (LIVC). The experiment was conducted in a single cylinder spray-guided direct injection spark ignition (SG-DISI) engine with liquefied petroleum gas (LPG). The injected fuel amount was fixed so as to investigate the effect of each strategy.
Technical Paper

First and Second Law Analyses of a Naturally-Aspirated, Miller Cycle, SI Engine with Late Intake Valve Closure

A naturally-aspirated, Miller cycle, Spark-Ignition (SI) engine that controls output with variable intake valve closure is compared to a conventionally-throttled engine using computer simulation. Based on First and Second Law analyses, the two load control strategies are compared in detail through one thermodynamic cycle at light load conditions and over a wide range of loads at 2000 rpm. The Miller Cycle engine can use late intake valve closure (LIVC) to control indicated output down to 35% of the maximum, but requires supplemental throttling at lighter loads. The First Law analysis shows that the Miller cycle increases indicated thermal efficiency at light loads by as much as 6.3%, primarily due to reductions in pumping and compression work while heat transfer losses are comparable.
Technical Paper

The Potential of the Variable Stroke Spark-Ignition Engine

A comprehensive quasi-dimensional computer simulation of the spark-ignition (SI) engine was used to explore part-load, fuel economy benefits of the Variable Stroke Engine (VSE) compared to the conventional throttled engine. First it was shown that varying stroke can replace conventional throttling to control engine load, without changing the engine characteristics. Subsequently, the effects of varying stroke on turbulence, burn rate, heat transfer, and pumping and friction losses were revealed. Finally these relationships were used to explain the behavior of the VSE as stroke is reduced. Under part load operation, it was shown that the VSE concept can improve brake specific fuel consumption by 18% to 21% for speeds ranging from 1500 to 3000 rpm. Further, at part load, NOx was reduced by up to 33%. Overall, this study provides insight into changes in processes within and outside the combustion chamber that cause the benefits and limitations of the VSE concept.
Technical Paper

Effects of Exhaust Throttling on Engine Performance and Residual Gas in an SI Engine

Combustion in engines can be controlled by the amount of residual gas, which has high temperature and heat capacity compared with fresh charge. Residual gas also acts like a dilution gas during combustion period. Accordingly, combustion duration increases, while the peak combustion temperature and nitrogen oxides (NOx) decreases. Amount of residual gas is affected by pressure difference between exhaust and intake, valve timing and engine speed. The main objective of this work is to identify the effects of exhaust throttle, valve timing and load conditions on residual gas fraction and engine performance. The intake valve open timing was varied freely under fixed exhaust valve close (EVC) timing. Additionally, exhaust throttle has been installed in the exhaust manifold to build up the exhaust back-pressure allowing extra amount of exhaust gases to be admitted into the cylinder during the valve overlap duration.
Journal Article

Characteristics of Turbocharger with TiAl Turbine Wheel in a Downsizing GDI Engine

Steady and transient tests in a downsizing Gasoline Direct Injection (GDI) in-line 4 cylinders 2.0 liter engine were carried out to investigate characteristics of turbocharger with Titanium aluminide (TiAl) turbine wheel. The density of TiAl material is lower than Inconel 718 (Inconel) which is raw material for conventional turbine wheel. The objective of this study was to investigate the effect of light rotational inertia of turbine wheel on engine performance. Performance of TiAl turbine wheel turbocharger itself was also compared to that of Inconel turbine wheel turbocharger. Except for the turbine wheels, all experimental conditions were matched to be the same load and engine speed conditions. The compressor total-to-total pressure ratio of TiAl turbocharger was higher under part load condition due to higher turbocharger speed of TiAl turbocharger, which was led by lower rotational inertia of TiAl turbine wheel, while the engine performance was not much improved.