Optimizing the Ignition Timing of a Converted CNG Mono-Gas Engine

Abstract

Governmental policies on renewable energy and environmental act are aggressively being enforced to mitigate recent climate change. Natural gas is not renewable but it is the most abundant and has the lowest Lifecycle CO2emission among fossil fuel. Realizing such promising alternative, many logistics and transportation companies are converting their existing diesel-fueled vehicle to CNG-fueled. Researchers have shown that CNG engines offer advantages compared to diesel and gasoline engines such as high efficiency and low emissions. Prior to this work, a 4.3L 4-cylinder diesel engine was modified and retrofitted with a CNG mono gas system. However, it was observed that the engine, CNG-fueled combustion is not stable especially at idling speed. The purpose of this study is to optimize the ignition timing best suited for idling both in normal operating mode (700-850 rpm) and in cold start mode (1000-2000 rpm). The ignition timings tested were 20oBTDC and 25oBTDC. The measurements were made at engine speeds from 700 to 2500 rpm. Some irregularities were found in the result, but overall, the ignition timing 25oBTDC is better than 20oBTDC in terms of fuel consumption and exhaust gas emissions. For this particular system, the results recommend that the idling engine speed should be at 700-800 RPM and 1500 RPM during the normal mode and cold start mode respectively. The use of engine speed of 1000 to 1300 rpm should be minimized to reduce overall exhaust gas emissions.