C # Microsoft.Speech.Recognition DictationGrammar ()

I have a problem using the Microsoft.Speech.Recognition library.

I'm trying to make a C # application with speech recognition. I need to recognize text spoken in pt-BR, but only rules configured using a Grammar (). I would like to recognize free text without being configured in the Grammar, for example for the user to speak some message to be displayed in a TextBox.

SpeechRecognitionEngine recognitionEngine recognitionEngine = new 
SpeechRecognitionEngine(); 
recognitionEngine.SetInputToDefaultAudioDevice(); 
recognitionEngine.LoadGrammar(new DictationGrammar()); 
RecognitionResult result = recognitionEngine.Recognize(new TimeSpan(0, 0, 20)); 
foreach (RecognizedWordUnit word in result.Words) 
{ 
     Console.Write(“{0} “, word.Text); 
}

Could someone help me or give a hint otherwise for free speech recognition without setting up the expected speech in a Grammar?