The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent that it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Catalytic converters may be used to reduce emissions. Generally, the catalytic converters are more efficient at elevated temperatures. For example, “a light-off temperature” is a point where the conversion of carbon monoxide (CO), unburned hydrocarbons (HC), and nitride oxides (NOx) has reached 50% efficiency. To more quickly increase the temperature of a catalytic converter, ignition timing may be retarded to generate more heat to the exhaust gas during the engine cold start period. The ignition timing retardation is generally achieved by shifting the spark timing from a point where the engine outputs a desired torque. Due to the spark timing shift, the engine may not output the desired engine torque.