Initial Results on a New Light-Duty 2.7L Opposed-Piston Gasoline Compression Ignition Multi-Cylinder Engine

Abstract

Gasoline compression ignition (GCI) is a cost-effective approach to achieving diesel-like efficiencies with low emissions. Traditional challenges with GCI arise at low-load conditions due to low charge temperatures causing combustion instability and at high-load conditions due to peak cylinder pressure and noise limitations. The fundamental architecture of the two-stroke Achates Power Opposed-Piston Engine (OP Engine) enables GCI by decoupling piston motion from cylinder scavenging, allowing for flexible and independent control of cylinder residual fraction and temperature leading to improved low load combustion. In addition, the high peak cylinder pressure and noise challenges at high-load operation are mitigated by the lower BMEP operation and faster heat release for the same pressure rise rate of the OP Engine. These advantages further solidify the performance benefits of the OP Engine and demonstrate the near-term feasibility of advanced combustion technologies, enabled by the opposed-piston architecture. This paper presents initial results from a steady state testing on a brand new 2.7L OP GCI multi-cylinder engine. A part of the recipe for successful GCI operation calls for high compression ratio, leading to higher combustion stability at low-loads, higher efficiencies, and lower cycle HC+NOx emissions. In addition, initial results on catalyst light-off mode with GCI are also presented. The OP Engine’s architectural advantages enable faster and earlier catalyst light-off while producing low emissions, which further improves cycle emissions and fuel consumption over conventional engines.

Optimizing the fuel efficiency of an opposed piston engine for electric power generation

“…In the compression phase, a hyperbolic tangent function is used to activate the auto-ignition integral only after the exhaust crankshaft has passed the pilot injection reference θ pilot . For the OP engine considered in this work, we utilize a model of gasoline compression ignition (GCI) using an pump gasoline with an 87 anti-knock index (AKI) due to the advantages detailed previously by Salvi et al 11 Therefore we consider a pilot and main heat release event where the start of combustion for the pilot heat release is governed by the chemical kinetics of the fuel and is modeled here using an ignition delay correlation. The ignition delay value in this case, τ id , is provided by the ignition delay correlation where the parameters were selected based on previous experimental data with the same 87 AKI gasoline.…”

“…The leaner operating conditions can reduce engine-out emissions and improve thermal efficiency. 10,11 The introduction and preliminary evaluation of a hybrid design utilizing electric machines attached directly to the two crankshafts of the OP engine to extract mechanical work from combustion and convert it to electricity was previously performed by the authors. 12 This work extends the previous study by evaluating the unique operational opportunity and challenges of using electric motors to independently control the engine crankshafts' motion.…”

“…The leaner operating conditions can reduce engine-out emissions and improve thermal efficiency. 10,11…”

Experimental study of the impact of scavenging efficiency on diesel combustion in an opposed-piston two-stroke engine

“…Experimental results indicated that GCI on the OP2S engine architecture resulted in higher efficiency, lower criteria pollutant operation of the OP2S engine compared to diesel combustion while simultaneously solving the low-load stability problem of GCI. 25,26 Similar to GCI, the OP2S engine architecture can address many of the challenges associated with compression ignition of high autoignition renewable fuels, like methanol and ethanol. Additionally, the alcohol fuels have a high charge cooling potential, due to their high heat of vaporization, and a near-zero sooting potential, due to their short carbon chain oxygenated fuel structure.…”

The Effect of Crankshaft Phasing and Port Timing Asymmetry on Opposed-Piston Engine Thermal Efficiency

“…Recall that the aim of this study is to investigate how crankshaft phasing and port height-to-stroke ratios affect thermal efficiency across the selected operating points. In terms of crankshaft phasing, the 0-20 • range in Table 5 is an extension of the 8-12 • exhaust crank angle lead range investigated by Achates Power on their opposed-piston GCI engine [42] (p. 3, Table 1), while the earlier Achates Power OP2S diesel engine employed a fixed 13.5 • crankshaft phase angle [43]. Regarding port heights, Yang et al suggest the optimal port height-to-stroke ratio should lay in the range 0.11-0.15 for most engines [34] (p. 345, Figure 23), while ranges of approx.…”